[HN Gopher] Why car wheels are so flat these days
___________________________________________________________________
Why car wheels are so flat these days
Author : CoffeeOnWrite
Score : 402 points
Date : 2022-09-14 03:40 UTC (19 hours ago)
(HTM) web link (www.theautopian.com)
(TXT) w3m dump (www.theautopian.com)
| roughly wrote:
| If you're any kind of a car person, you owe it to yourself to
| check out the rest of The Autopian - it's an independent car site
| founded, owned, and operated by deeply weird car people, and it's
| absolutely amazing.
|
| Here's their writeup on the electric F-150 - keep scrolling on
| that page, and look at the kind of depth and detail they get
| into: https://www.theautopian.com/the-2022-ford-lightning-is-
| just-...
|
| The site is a gem.
| EdwardDiego wrote:
| That was a great article that makes me very happy about how
| Ford are approaching EV utes, I've often noted the tendency to
| make EVs weirder than their ICE equivalents. Well done Ford.
| 6stringmerc wrote:
| Thanks for sharing, I have a weirdo car loving fun friend into
| RC stuff and maybe he can help them with some sidebar content.
| This is super!
| 1letterunixname wrote:
| _Scotty Kilmer from Houston enters the chat to talk about how
| new cars are plastic garbage and how their low profile tires
| look "cool" but are woefully fragile._
| dzonga wrote:
| n that the only car worth buying is '91 Toyota Celica
| mmmpop wrote:
| bro but rotary engines, you need an RX7 or I hear GT3000s
| are fast and shit but your bank probably won't give you a
| loan for a used Mitsubishi. maybe your mom will let you
| hold on rent for a bit??
| msla wrote:
| New cars are so fragile, they deform into scrap instead of
| transmitting the force to the occupants!
| throwaway0a5e wrote:
| Crumple zones perform a very specific function in the
| sequence of airbag deployment (letting the sensors crash
| and bags deploy before the cabin starts decelerating). The
| speed window at which they will appreciably reduce the
| deceleration in the cabin is well below the speeds at which
| a seat-belted occupant of an airbag equipped vehicle has to
| worry about serious injury. Crumple zones are undeserving
| of the worship they get. If you want to worship something
| worship side curtain airbags. They save a lot more life and
| injury than crumple zones. Pre-tensioners are also another
| feature that I'd rather have than a crumple zone. As a
| general rule, features that directly keep the occupants
| from hitting things are far more beneficial to outcomes
| than stuff that acts upon the whole vehicle.
|
| Secondly, it is perfectly possible to design cars that do
| not need tons of invasive repairs from minor fender
| benders. Revise bumper and front/rear cosmetic design to
| allow for effective bumpers (see also: the 1980s) and tune
| crumple zones to need higher forces to deform them so you
| don't have to potentially replace a whole car over a
| 10-15mph collision. The tradeoff here is that the speed
| range at which crumple zones do much would move up which is
| good for real world performance bad for scoring that
| perfect five stars in a low speed lab test that actually
| helps sell cars.
| tempestn wrote:
| If you're going to make blanket assertions that safety
| tests are invalid and/or that the engineers designing
| cars don't know what they're doing, some references are
| probably called for.
| throwaway0a5e wrote:
| > If you're going to make blanket assertions that safety
| tests are invalid and/or that the engineers designing
| cars don't know what they're doing, some references are
| probably called for.
|
| Can you please cite where I stated, or hell, I'll settle
| for strongly implied, "the safety tests are invalid" or
| that "the engineers designing cars don't know what
| they're doing".
|
| The person I am replying to made a trite low effort
| comment. I, without calling them out like they deserved,
| explained that the situation is more nuanced and their
| opinion is slightly off mark. You then replied with
| another trite low effort comment straw-manning me. FFS
| this is ridiculous.
| jackmott wrote:
| Well the fragility of low profile wheel/tire packages is true
| at least
| prottog wrote:
| He actually moved to Tennessee!
| boringg wrote:
| Just took a quick scan - funny, intelligent, in-depth technical
| content in here but very approachable. This has definitely
| hackernews community quality to it.
|
| Thought this was interesting: https://www.theautopian.com/this-
| junky-postal-jeep-with-a-ch...
| dangus wrote:
| Very cool site indeed.
|
| Looking at photos of the F-150 Lightning chassis, it seems like
| a pickup truck's body-on-frame design has a nice unintended
| benefit of being easy to convert to electric. The "frame"
| doesn't look so different from the "skateboard" EV design
| that's common.
|
| A lot of converted gas to EV cars like the Genesis Electrified
| GV80 rob interior space for shoehorned batteries, but the F-150
| is all gains with that massive front trunk.
| rob74 wrote:
| I can't really understand the author's (and apparently some
| designers') fetish about "deep dish" wheels. If a flat wheel
| allows better technical solutions and even improves aerodynamics,
| I'm all for flat wheels! Hell, even Formula 1 cars (which used to
| have the "deepest" wheels ever) use hubcaps since this season
| (https://the-race.com/formula-1/gary-anderson-how-f1s-new-
| whe...). Maybe that will make "flat wheels" sexy? We will have to
| wait and see...
| a3w wrote:
| AFAIC a higher rubber shell slightly helps with suspension.
|
| Thin wheels help with aquaplaning/hydroplaning (strongly) and
| slightly with reducing consumption.
|
| Most wide wheels available to consumers are thick, so that is a
| tradeoff that happens with the new design, although I might mix
| up physical ratio, price and street legality, due to having
| only looked at one car.
| jerlam wrote:
| There are a lot of car things that have no functional benefit,
| but exist because they used to mean something (but not anymore)
| or are useful at racing speeds but not at normal ones, or are
| simply traditional.
|
| One I find particularly amusing is the Ford Mustang Mach-E, a
| fully battery-powered vehicle, has the ability to play fake
| engine noise through the cabin speakers because some drivers
| think engine noise is a feature of "real cars".
| 6stringmerc wrote:
| It's not even an electric car thing - my Focus ST came from
| the factory with a little sound pipe thingy from the engine
| to the cabin to make it feel more racy. When I bought it used
| it was disconnected, which is fine, because the MBRP 2.5" cat
| back exhaust already installed is about 3x louder than stock.
|
| I'm pretty sure BMW was doing it too when they started going
| all turbo and losing the song of the NA.
| GordonS wrote:
| I drove a BMW x5 a couple of years back, and it piped fake
| engine noise into the cabin. IIRC, it was a petrol v6/v8,
| so was quite capable of making it's own sound, so the whole
| thing was pointless - but worse, the fake engine noise
| sounded totally fake! Honestly, I felt pretty silly with it
| enabled!
| doubled112 wrote:
| > quite capable of making it's own sound
|
| But so isolated from the world around it that you can't
| hear it.
| KMnO4 wrote:
| In a way, I'm kinda fine with this.
|
| There a lot of things that make a car _feel_ faster, and
| giving them higher displacement engines and louder exhausts
| has more disadvantages than it's worth for most people.
|
| You can get the same experience with slightly more cabin
| noise (that doesn't annoy your neighbours), a longer first
| gear, kickdown pedal, etc.
|
| It's kinda like Coke Zero. If you can get 95% of the same
| experience, why opt for the sugar?
| 11235813213455 wrote:
| I thought it'd be about reducing wear. Note that tyres are a
| massive air pollution contributor https://www.polytechnique-
| insights.com/en/columns/planet/are...
| blowski wrote:
| The BBC's "More or Less" pointed out some of the claims about
| tyres being a major contributor to air pollution are
| exaggerated. One of the claims was based on the total amount of
| wear from tyres as weight, without considering that most of
| that wear is made of very large particles that remain on the
| ground.
| 11235813213455 wrote:
| The link I gave has serious sources, and "remains on the
| ground" is a bit vague, a large amount of air pollution is
| just dust from the road and elsewhere raised up by cars
| marginalia_nu wrote:
| Some of the data confirming the hypothesis may be from
| looking at studded snow tires. They tear up a lot of crap in
| the air if you use them on roads that aren't covered in ice.
| kube-system wrote:
| The best thing that improved tire wear is just better tire
| construction.
| bagels wrote:
| It's talking about the outward facing surface of the wheels,
| when referencing 'flat', not the tires.
| userbinator wrote:
| For comparison, here's the front suspension of a 1956 Buick:
|
| http://buick.oldcarmanualproject.com/manuals/1956/1956%20Bui...
|
| Observe that the kingpin axis is entirely inboard of the tire,
| almost vertical, and the scrub radius is such that the axis meets
| the ground _inboard_ of the contact patch of the tire (in other
| words, it doesn 't really "scrub" the tire when turning).
|
| _What stops the suspension from actually steering is the
| steering system itself and the hands of the driver holding the
| wheel. You can visualize that in the picture above or below; if
| the ground pushes the tire rearwards at the contact patch, which
| is a few millimeters outboard of where the kingpin axis
| intersects with the ground, that tire will have a tendency to
| rotate, which will pull on the steering tie rod and send forces
| to the steering wheel._
|
| What isn't mentioned is that if you're braking, then the wheel on
| the other side also has the same force applied to it; only the
| difference between the two forces is what attempts to back-drive
| the steering system.
|
| Note that it is harder with rack-and-pinion to approximate
| https://en.wikipedia.org/wiki/Ackermann_steering_geometry which
| is advantageous for tire wear.
|
| Personally, I prefer the smoother and more isolated steering feel
| of a traditional recirculating-ball system, but then again, I'm
| not the type of driver who likes fast cornering.
| ehnto wrote:
| I've never driven a car with that kind of suspension, does the
| design still use caster to self-center the steering, or will
| the tires stay roughly where you point them even if you let go?
| xattt wrote:
| I thought this was the result of front wheel drive.
| ehnto wrote:
| Rear wheel drive cars also do it. The caster on a car
| mimics that of the wheel of a shopping cart. Having the
| pivot axis be at a slight angle relative to the direction
| your travelling makes the wheels trail behind that axis.
|
| It does tend to be more apparent in front wheel drive cars,
| perhaps it's the weight of the motor? It's really important
| to get right in motorsport, as it denotes the
| characteristics of the car when you've oversteered. A car
| with correctly set caster will "self steer" itself back to
| straight without any driver input, and it will guide the
| car while oversteered in a way that's balanced with the
| direction the car's actually heading rather than where it's
| pointing (if you're intending to be sideways, like in
| drifting).
| asmithmd1 wrote:
| Yes, you have to have caster or the car would be very
| difficult to drive. I had a VW bug with a worm gear steering
| box that was going bad. It would _almost_ keep the wheels
| wherever you put them and it was scary to drive. Think about
| how you let the steering wheel slip as the wheels return to
| straight when you turn onto a cross road, you had to return
| the wheels to straight yourself.
| autotech wrote:
| The equalizing brake force from the other side sounds good
| until you factor in things like ride height differences from
| worn suspension or imperfect roads. Those and other transient
| forces disturb that left to right balance. Weird things like
| bump steer start happening when left to right measurements are
| off.
| Gordonjcp wrote:
| You'd loved DIRAVI like on old Citroen CXes then. Instead of a
| big spring in the Danfoss valve between the steering column and
| rack it had a little gearbox with a kind of "dogbone link"
| joining the two, that got pushed from side to side if there was
| a difference between the rack position and steering column
| position to push the valve. Then there was a kind of heart-
| shaped cam that pushed the steering wheel back to the centre,
| with a spring pressing against it controlled by hydraulic
| pressure from a speed sensor on the gearbox. The faster you
| went the harder it pressed the spring until at 70mph you could
| barely move the steering wheel but the slightest pressure would
| steer quite quickly.
|
| Until you got used to its incredibly sensitive response (about
| 1.5 turns lock-to-lock) you tended to drive in zig-zags like
| you were tacking a dinghy up the road, but once you did get
| used to it nothing ever felt as precise or comfortable. I've
| driven some incredibly "sporty" cars, "cost as much as a house"
| end of the market cars, and none of them got close to the CX
| for steering feel.
|
| The earlier GS and GSA had inboard front disc brakes on the
| side of the gearbox, allowing them to be massive while also
| allowing the tall skinny tyres (145SR80, about 150mm wide) to
| be absolutely centred on the kingpin, boresighted on the middle
| of the contact patch. They had incredible handling, so sharp
| and responsive, and the non-powered steering was as light as
| any modern car at parking speeds.
| Swizec wrote:
| This is a great example of the illusion of explanatory depth [1]
|
| You read the title and think "D'oh obviously traction", then you
| see the first picture in the article and think "Yep, obviously
| flatter tyres because traction", then you read a little more and
| think "Wait, what do they mean by flat?", ...
|
| ... and then it just keeps going deeper and deeper into this
| rabbit hole you never considered before and barely even noticed.
| You realize you didn't know shit.
|
| The explanation ends up being steering feedback forces. Now I
| wonder if we can have deeper wheels again with modern electric
| motor power steering.
|
| [^1] https://thedecisionlab.com/biases/the-illusion-of-
| explanator...
|
| https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3062901/
| jasonjayr wrote:
| > The explanation ends up being steering feedback forces.
|
| .... which, is used to communicate traction status back to the
| driver:
|
| > The ability of forces to feed back to the driver meant there
| was significantly more "feel" for what the tires were doing and
| where the limits of adhesion were. (from the article)
| fnordpiglet wrote:
| There's a section on aerodynamics that explains why for any
| vehicle but especially EV's can benefit. They give an example
| that flat wheels improve a model S coefficient of drag by 12%.
| t43562 wrote:
| I would have enjoyed this but didn't understand it. I think the
| main problem is that I didn't understand what they meant by tyres
| "being flat" so the rest of it was impossible to grok.
| Traster wrote:
| They that the face which you put the bolts through is flat. On
| older cars it was concave.
| larrik wrote:
| I didn't follow what they meant for a while either. This image
| helped: https://images-
| stag.jazelc.com/uploads/theautopian-m2en/cher...
|
| It's not the tires that are flat, it's the face of the rims.
| post-it wrote:
| Ohh. I thought at first it was talking about round, donut-
| shaped vs thin, cylindrical tires.
| maxerickson wrote:
| It's not about the tires, it's about the wheels (maybe calling
| them "rims" makes the connection).
|
| The parts of the suspension the wheel turns on are pushed out
| towards the center of the contact patch on newer cars to reduce
| the forces that feed back to the steering wheel. The different
| steering system used on older cars benefited from those larger
| forces (because the systems didn't have good feedback).
| raisedbyninjas wrote:
| Well, they said the wheels are flat, not the tires.
| ksd482 wrote:
| The part of the tire that touches the road is flat as opposed
| to being curved.
| Traster wrote:
| I think it's actually not - they mean the side face of the
| wheel, https://images-
| stag.jazelc.com/uploads/theautopian-m2en/cher...
|
| They're talking about the wheels, not the tyres.
| starkd wrote:
| The newer tires also have the appearance of being flatter.
| This may be where the confusion is.
| starkd wrote:
| It did fail to define some terms. Also, it would have been nice
| to show on the diagrams the direction of the forces involved.
| It's a bit difficult to visualize precisely.
| TekMol wrote:
| Does anybody actually enjoy this type of type of SEO content?
|
| Stuffed with filler words to the max. _Maybe_ there is an answer
| to the title somewhere on the page. But the way it is written, it
| just stole my time until I gave up after a few paragraphs of
| filler content. First sentence: Have you ever
| wondered why designers show sketches of concept cars with
| massive deep dish wheels, but when those cars actually
| make it to production the wheels end up being fairly
| flat?
|
| No. I just followed a link "Why car wheels are so flat these
| days" and was interested in the answer.
|
| Compare that to a classic essay "A plan for spam" by Paul Graham:
|
| http://paulgraham.com/spam.html
|
| First sentence: I think it's possible to stop
| spam, and that content-based filters are the way to do
| it.
|
| That's the type of content I would like to see on HN.
|
| If it was 2022 style SEO content, PG's essay would have started
| with "Have you ever wondered why you get so much spam into your
| inbox these days and why that spam is so terribly boring,
| sprinkled with typos and ads, often full of images and links, and
| what you could do to get rid of it?". Shudder.
| P5fRxh5kUvp2th wrote:
| I scanned, didn't find the answer quickly, and closed the tab.
|
| I'm with you, I seriously hate that I have to read the internet
| that way nowadays.
| Double_a_92 wrote:
| To be fair that's how we were thought to write essays in
| school... But I also find those overly long articles that don't
| say anything annoying.
| CamperBob2 wrote:
| This isn't really an example of SEO content. If it were, it
| would ramble on for multiple paragraphs (and page/ad breaks)
| before getting to the point.
| jallasprit wrote:
| While I agree with the basic sentiment, this article is the
| type of article I will usually just skim fairly quickly,
| skipping sections if they aren't connected to the title.
| roughly wrote:
| That article was in part a reference to another article from
| the site:
|
| https://www.theautopian.com/this-is-why-car-designers-always...
|
| Which was in part a reference to some questions on the comment
| threads from other articles in which a designer sketched some
| car ideas on that site.
|
| So, you may not have wondered that, but someone on the site
| wondered that, and another writer on the site, who, granted,
| has an background in engineering car suspensions, not writing,
| wrote this article in response.
| bryanrasmussen wrote:
| This does not seem to be a SEO content pushed out by some
| content farm to me (although I don't have expertise in the area
| being written about) the article seems like there was quite a
| bit of work put into it; I think probably the writer is just
| not as succinct as you would like.
| Kaibeezy wrote:
| Agree. I was both interested enough to read the whole article
| AND really annoyed at the fluff. ("let me explain", "of
| course", "we'll get back to that") Bleh.
| pmontra wrote:
| Papers have an abstract with a summary of the results then go
| on for pages explaining the long road to them. Maybe that could
| be a format to mimic and appease both kind of audiences: people
| with no time or interest to learn all the details and
| enthusiasts that want to read everything about the subject.
| dotancohen wrote:
| For what it's worth, I hate the fluff. But the information
| buried within was very interesting. Unfortunately, with a
| single dominant gatekeeper to all the web's content, that
| gatekeeper dictates how people will write.
|
| That said, I understand Google's position. Back in the
| WildWildWest days of the WorldWideWeb, Google made the change
| from preferring keyword-based text to preferring written-for-
| humans text. But the target humans seem to those who read for
| love of reading, as judged by lit majors. Now I've been teased
| since kindergarten for my love of reading, but as a
| professional I want concise and terse, not an overabundance of
| anecdotes and adjectives. But the lit majors who influenced the
| post-2008 spider algorithms correctly for the time influenced a
| preference for the later.
|
| Hopefully sometime Google will figure out that technical texts
| should be keyword based, and literary texts should be for-
| humans, whatever that is deemed to mean. And Google might
| provide either a feature to choose the algorithm, or more
| likely, try to guess based on heuristics.
| kccqzy wrote:
| I think the article is fine. You might just be an impatient
| reader.
| Double_a_92 wrote:
| Well it's a random thing thrown at me on HackerNews... I
| don't care that much about car wheels to invest several
| minutes into reading about this completely random fact.
| Either it tells me relatively quickly, or I stop caring.
| jimjimjim wrote:
| what is an attention span...
| bunabhucan wrote:
| Mechanical engineer here, this article could have more detail
| and I'd have read it. The translation from nuts and bolts and
| rods and links in the suspension to the intangible but
| apparently important (for selling cars) "feel" is fascinating.
| It's sometimes idiotic - "make an Audi Q7 feel like a Porsche"
| required a movable central connection in the rear suspension
| for some rear wheel steer (but just using the existing
| play/travel) as well as a hydraulic then (v2) electric doo dah
| to counteract the tilt and keep the boat of a car level through
| turns. There's no "point" to this - it just let's them sell a
| souped up big SUV at 911 prices and make money hand over fist.
|
| I'm not even a car person but this article wasn't laboring the
| point.
| retcore wrote:
| Hang on, so multi tonne vehicles are designed with the
| rolling stock equivalent of anaerodynamic stability managed
| by black boxes?
|
| I guess this is situated for latency but more likely
| installation and loom cost controls, close to the rear axle
| therefore more exposed to moving accident damage and at least
| to my casual reading of owner enthusiast fora unknown to
| educated owners and the public - rather like the Eurofighter
| Typhoon?
|
| How can such designs pass DMV / MOT tests with inherent
| rolling instability in failure mode?
|
| Or is there failsafe?
|
| Edit: I should have said multi tonne vehicles intended by
| design to be driven fast and at limits including load limits.
| DiggyJohnson wrote:
| I confused as to why the feel of a car driven at road speeds
| isn't a "real"/valuable/relevant selling point in road cars.
| That's a huge factor in my car purchases, and it's the thing
| I remember most about my old cars.
| dotancohen wrote:
| Because that's not something that is typically checking in
| "test drives" nowadays. I was once yelled at by the Renault
| saleswoman for braking too hard during a test drive, even
| though I told here that I'm about to perform an emergency
| stop. She had us return to the dealership. I happily bought
| a Focus instead, the very next day, after a proper test
| drive.
|
| But don't get me started on them providing a rear-disc-
| brake Focus for the test drive even though the trim level I
| was interested in had rear drums. Had I driven the drum
| model, I would not have bought it. But I acknowledge that
| I'm an outlier, who actually cares about how the vehicle
| handles and accelerates and brakes and takes potholes and
| how noisy it is at highway speeds and how it fares in a
| cross wind. The common, typical "test drive" doesn't cover
| any of those aspects anymore.
| DiggyJohnson wrote:
| I appreciate this comment, and read the entire thing in
| Dwight Shrute's voice.
| solardev wrote:
| I agree. Took way too long to get to the point.
| dieselgate wrote:
| Huh? Didn't get that vibe at all. This article is actually just
| what I was looking for to begin learning about steering
| systems, from a technical but high level, before doing some
| maintenance work on a truck.
| hrbf wrote:
| Same here. Was interested in the answer but I gave up before
| getting to a satisfactory conclusion. Way too little
| information density.
| joshu wrote:
| This seems like a nice article. I think you are off base.
| Roark66 wrote:
| I start to think these days one has to write like this and fill
| the page with 2k words of fluff before getting to the point if
| one hopes the website to show up in Google.
|
| I recently struggled a lot with a technical problem. I searched
| and searched and I couldn't find a solution. Then I discovered
| a solution myself and I created a short blog-style tutorial how
| to resolve it.
|
| As far as I know the only one on the Web, but does it show in
| Google search results when one searches for exact phrase or
| quite rare keywords used? No way, I've added it to Google,
| Google scanned it, and that's it.
|
| Searching for the problem you find my forum posts where I ask
| (unsuccessfully) for help about it and maybe few more people
| doing the same,nothing more.
|
| Perhaps instead of writing my blog entry for humans (state the
| problem, describe a solution). I should've written it for
| Google bot in a format of:
|
| - State a problem - why do we have this problem - what is the
| history of stuff we have the problem with - a personal story
| how I saved my dog while working on the solution - at the very
| end one sentence that hints at a solution (don't just give it
| away! Make 5 pages talking about it instead!)
|
| That's why we can't have nice things.
| maven29 wrote:
| Try github gist or creating a stackoverflow question and
| answering it, I find that even short snippets are indexed
| well on whitelisted platforms like these.
| blowski wrote:
| I enjoyed it. I learned something, the article delivered on the
| title.
| goldenchrome wrote:
| I think you're being overly harsh. This is a post on a website
| for car enthusiasts. Car enthusiasts do in fact look at
| artist's renders of cars because they're genuinely into car
| culture. I think it's an effective hook.
|
| If you just want a straightforward answer then Google it and
| perhaps Google can find the right snippet that you can ingest
| in 8 seconds.
|
| HN isn't a feed for TekMol's interests.
| dreamcompiler wrote:
| Related question: Why must brakes be _inside_ the wheels rather
| than inboard on the axle? Why not weld disks onto the axle
| inboard of the wheels and put the brakes there? That would make
| more room inside the wheels.
|
| Of course on undriven front wheels it wouldn't work because there
| is no axle, but in front-wheel-drive cars there is one. The
| brakes could be inboard of the CV joint, no?
| tricky wrote:
| See the inboard brakes on 60's Jaguars - Sure, the unsprung
| weight and improved handling is nice but they are much harder
| to maintain because 1. you have to lift the car to see if they
| are worn and 2. if you have to repair a caliper it is almost
| easier to drop the entire rear suspension than to try to dig
| the caliper out while everything is on the car.
| rr888 wrote:
| Because then you'd get a huge amount of torque between the
| brakes and the wheel, esp through the CV joint it'd be
| unnecessarily brutal. On the back wheels it could be possible,
| on the front (where most of the braking is) unlikely.
| throwaway0a5e wrote:
| If the CV joint can handle peeling out it can handle brake
| torque. The link between tire and ground is basically always
| the weak point.
| jcampbell1 wrote:
| Cars have about 700hp of braking. Drop a 700hp motor in a
| car and have fun using the factory CV/half shafts.
| throwaway0a5e wrote:
| You won't break anything without some big sticky tires to
| transmit that power to the ground and that (but for
| braking) is exactly my point.
| rr888 wrote:
| If the wheel is sliding the torque on the wheel will be
| lower than if the tires were grippier. I guess the
| comparison is if braking is high (de)-acceleration than the
| engine. I'm thinking your idea has a lot of the same
| stresses as engine braking.
| Unklejoe wrote:
| I'm not sure about that. Most cars can stop way faster than
| they can accelerate. The differences in force would be even
| more extreme for front wheel drive cars where the weight
| transfer allows for more grip on the front wheels during
| braking compared to accelerating or peeling out.
| windowsrookie wrote:
| Two reasons.
|
| 1. Brakes generate massive amount of heat and need cooling.
| There is a ton of airflow down at the wheels, some wheels are
| even designed to direct more airflow to the brakes.
|
| 2. Because changing brakes down at the wheels takes 20 minutes
| with the proper tools. If you move them inboard and affix the
| rotor to the axle you would significantly increase labor time
| and cost in replacing the brakes.
| TheCapn wrote:
| Both good reasons but I'd argue #2 is not considered by the
| engineering in practical reality. Have you seen the lengths
| some manufacturers require people to go through for things
| like a simple battery replacement? headlight bulb change? Or
| even in some cases the hoops to jump through for an oil
| change? There's some extreme examples out there of each, I
| heard horror stories from my friend who used to do automotive
| mechanical work (alternators only reachable by dropping the
| engine) and there's countless stories over at reddit's
| /r/Justrolledintotheshop
| hoosieree wrote:
| As others said, accessibility and cooling. But inboard brakes
| are still popular in some niche areas, like sandrails:
|
| https://www.dieselworldmag.com/wp-content/uploads/2017/03/DW...
|
| This particular example doesn't even _have_ front brakes.
| theluketaylor wrote:
| Some cars have had inboard brakes to reduce unsprung mass. Alfa
| Romeo did it a lot in the 70s and 80s.
|
| There are a lot of downsides, like maintenance is a bit of a
| nightmare.
| fsckboy wrote:
| in order to figure out what this article is saying, I have to
| learn a lot of terms, and I don't think it's going to be that
| astonishing or "aha!" so it doesn't seem worth it. The positive
| scrub ratio measured along the kingpin axis from the kingpin
| center... if only I knew what a deep dish wheel was as opposed to
| a flat wheel...
| lozenge wrote:
| It's not the width of the tire. Think of the tire like a
| cylinder - it's how the flat face of the tire tapers to the non
| flat one.
| skybrian wrote:
| Study the pictures. They mean how far inward the hub and spokes
| are indented compared to the tire rims.
| fsckboy wrote:
| you need to afix another point in your picture. Imagine a
| basic wheel mounted on the end of a solid axle. Now imagine
| that you made the axle shorter and replaced the wheel hub
| with a cone ("deep-dish") that has the tire mounted on the
| rim at the wide end of the cone. Did you change anything
| other than angular momentum (I guess I should say polar
| moment)?
|
| if you want to say, "you can't use a cone like that because
| there needs to be a hinge on the axle at this point for the
| wheel to steer-turn" then we've arrived at the reason for the
| limit on deep dishes? or if it's some other reason, it still
| doesn't seem that hard to describe.
|
| what I'm really saying is, the geometric concepts could be
| taught more simply without the all terminology. My older
| brother raced cars that he fixed and modified himself, so I
| grew up basically in a mechanic's shop. That was a long time
| ago so it's fine if terminology and concepts have changed,
| but I have a big head start over the average person and I
| found the article annoyingly incomprehensible
| ForHackernews wrote:
| Just watch this video, he explains it all very clearly:
| https://www.youtube.com/watch?v=MXW0bx_Ooq4
| mikotodomo wrote:
| For anyone else who got stuck for 40 minutes on the first
| paragraph with the "what am I looking at" image, see it compared
| to this later one. What we're seeing is the front of the wheel.
| https://images-stag.jazelc.com/uploads/theautopian-m2en/Scre...
| https://images-stag.jazelc.com/uploads/theautopian-m2en/Scre...
| londons_explore wrote:
| One day, I believe car design regulations will be amended to
| allow fully electric braking (ie. no hydraulics, drums, rotors,
| or pads). At that point, the motor can be moved into the wheel
| (unsprung mass = bad, but weight savings from not needing an axle
| or gearbox will outweigh this). Suspension and steering design is
| then far easier, because there is no axle to need to keep
| straight.
|
| Braking redundancy will be achieved by having motors/brakes on
| all four wheels, and within each motor 3 independant phase coils
| with independant controllers, such that there are effectively 12
| brakes on a car. Normally the controllers work together for
| smooth braking, traction control, software differential, etc. But
| even after 3+ failures braking performance should still be
| satisfactory for an emergency stop.
|
| Obviously braking energy needs to go somewhere. In the happy
| case, it's regen'ed into a battery. If the battery can't accept
| it, it gets dumped into dump resistors. If the dump resistors
| fail, it gets dumped into motor coils (of which there are 12
| remember). Obviously the motor coils will heat up very fast, so
| this is probably a one-use-only failsafe, like airbags.
|
| So the whole system (except the pedal itself) is 12 way
| redundant.
| manholio wrote:
| You should take into account that regen braking (even with
| resistors) only works at high rpm. The final phase of the
| braking you need to put even more energy into the coils on top
| of what the they already must dissipate for braking the car.
| Electrically, you would need to run the engine in reverse to
| come to a full stop.
| kwhitefoot wrote:
| > You should take into account that regen braking (even with
| resistors) only works at high rpm.
|
| It's note _even with resistors_ it 's _only with resistive
| braking_ that this applies.
|
| If this is an electric car then the inverter can be
| programmed to give pretty much any braking force you desire
| just by altering the phase of the driving waveform. This can
| be done at any rotational speed.
|
| My Model S can dump 50 kW back into the battery so long as
| the battery is not fully charged. At 60 km/h the kinetic
| energy of the car is about 300kJ so the car can be brought to
| a stop in about six seconds purely by regenerative braking.
|
| In the final phase of braking the car has hardly any kinetic
| energy left so the huge 250 kW motors can easily bring the
| car to a halt and hold the car still just by balancing the
| magnetic forces in the motor against the motion of the car or
| gravity. In fact this is exactly what it does when running on
| traffic aware cruise control in stop go traffic, whether on
| level ground or on steep slopes.
| afiori wrote:
| Most importantly it would also allow to go away with the
| steering wheel and make cars with Tank Controls* as god
| intended.
|
| I jest, of course, but I would kind of like to drive a car with
| steampunk levers more in theme with the giant spider in Wild
| Wild West.
|
| * https://en.wikipedia.org/wiki/Tank_controls
| thallium205 wrote:
| Most higher end electric stand-up scooters are actually setup
| this way.
| mellavora wrote:
| and tend to weigh a lot less than cars and also travel a lot
| slower, where e = mv^2
| btbuildem wrote:
| In the same vein, they tend to have much smaller motors,
| and the weight of the occupant is 10x the weight of the
| vehicle.
| ComputerGuru wrote:
| > Obviously the motor coils will heat up very fast, so this is
| probably a one-use-only failsafe, like airbags.
|
| Replacing airbags (at least individually) is cheap enough.
| Having your entire engine-equivalent need a replacement just to
| reduce the sprung weight?
| bilsbie wrote:
| This could vastly improve ABS too. Right? We wouldn't have to
| deal with pulsating pads and could adjust force in
| milliseconds.
|
| And maintenance would be way cheaper. Just remove the wheel and
| put a new one on.
| ryukafalz wrote:
| This is interesting because it also potentially solves the
| problem of particulate pollution from brake dust. There'd still
| be pollution from tire wear so it's not a perfect fix but it
| gets partway there!
| ben_w wrote:
| I don't claim any physical engineering skills, but don't you
| need a mechanical (non electrical) system for parking breaks?
| jasode wrote:
| _> , but don't you need a mechanical (non electrical) system
| for parking breaks?_
|
| To some of the replies... I think some clarification needed
| because the wording caused folks to think of something else
| such as _electronically _controlled__ physical brake pads:
| https://en.wikipedia.org/wiki/Electronic_parking_brake
|
| I think the gp was trying to ask about feasibility of
| _electric _powered_ magnetic field resistance braking_ ...
| similar to an exercise bike ... which would require _constant
| electrical power source_. (Similar to : https://www.google.co
| m/search?q=magnetic+resistant+braking+o...)
|
| Magnetic field resistance brakes is practical for
| regenerative braking but not safe for parking brakes on an
| incline if the batteries run out of juice. The context is the
| gp's premise of no physical friction brake components via _"
| (ie. no hydraulics, drums, rotors, or pads)."_
| KingJulian wrote:
| I would think so too. Any parking brake has to be a fail-safe
| type brake which has to function in the absence of
| electricity. Hence, as you mentioned, purely mechanical.
| kwhitefoot wrote:
| It only has to remain engaged, engaging it in cars with
| push button parking brakes requires electricity to drive a
| small electric motor at each wheel.
| Sohcahtoa82 wrote:
| They need to be able to remain applied without power, but
| the application can require power.
|
| In my Tesla, I push a button and I can hear an electric
| motor engaging the brake.
| 2III7 wrote:
| You don't, many modern cars have electronic parking brakes
| with small electric motors mounted on the rear calipers which
| push the brake pads against the discs when activated.
| nicoburns wrote:
| If it's using brake pads, then it's still a partially
| mechanical suggestion. The comment at the top of the thread
| was suggesting doing away with brake pads entirely!
| forgetfreeman wrote:
| I am very glad you commented here as my initial skepticism
| of your claim lead me to do a spot of research that
| answered several unresolved questions I'd had about one of
| the most obnoxious features I've ever seen in a new car. My
| mother in law has a car with (apparently) electronic
| parking brake and I have loathed everything about it from
| the moment I first sat down in the car. This at least
| explains why an utterly unintuitive double toggle button
| replaced the "standard" mechanical lever on the center
| console and what notional benefits (hill holding) come with
| this system. I'd hate this a lot less if the manufacturer
| had included a tell-tale of some kind to visually indicate
| if/when the ECM thinks the P-brake is engaged.
| londons_explore wrote:
| You do, yes. But that can be a metal pin the size of your
| pinky finger. It's a super easy engineering challenge
| compared to the regular brakes that slow down the car, which,
| when emergency braking a 2 ton car from 100 mph, needs to
| briefly absorb nearly 1 megawatt. Thats the power used by
| 1000 houses, which is a lot to absorb in a lightweight system
| that needs to still work if part of the system fails.
| thatcat wrote:
| The parking brake is the emergency brake, cant be a pin
| hollywood_court wrote:
| Nope. Many modern vehicles have push button electric parking
| brakes.
| OJFord wrote:
| With no axle it'd also be a lot easier to allow them to turn 90
| degrees (or 360(+), I'm just not sure there's any point), and
| have all-wheel turning, for optimal (and stupidly easy)
| parallel parking.
|
| I used to make Lego vehicles like that (well before I could
| drive), because it felt so silly as a passenger being parallel
| parked I suppose.
| mvgoogler wrote:
| Is the Aptera doing this? I remember them talking about having
| the motors in the wheels but I'm not sure if it's what you're
| proposing.
| jonfw wrote:
| Modern brake systems are so good though, they're cheap,
| powerful, reliable, and easy to service. I am not sure that the
| juice would be worth the squeeze
| whiplash451 wrote:
| Not a mechanical engineer. This design is interesting. Do you
| think regulation is the only reason this did not happen yet?
| Why is nobody building this otherwise?
| londons_explore wrote:
| The main reasons against this are:
|
| * Regulation. Plenty of countries are very specific about the
| exact mechanicals of brakes, in laws that are 100+ years old
| from when runaway cars killed people.
|
| * Unsprung mass. Cars handle better if the wheels are very
| light and all heavy bits are in the body of the car.
|
| * Large diameter motors are harder to design - there is no
| opportunity for a gearbox, so you lose one design parameter,
| and need the motor magnetics to be right around the rim of
| the wheel to make up for it.
|
| * Difficulty of making the air gap within the motor very thin
| at such large diameters - you end up needing super large
| diameter roller bearings.
|
| However, I think despite those downsides, the benefits
| outweigh them.
| meragrin_ wrote:
| What about potholes? Wouldn't they lead to the premature
| death of the motors if not the wheels themselves?
| wrycoder wrote:
| Also, more exposed to salt spray than inboard motors.
| sdk16420 wrote:
| Drum brakes are in the same spot and can last for the
| life of the vehicle.
| orangepurple wrote:
| That's how they will make money after their current
| golden goose, automatic transmissions with "lifetime oil
| changes," is exhausted.
| bradfa wrote:
| 2 main reasons I can think of (tl;dr: cost):
|
| 1. Braking generates a _LOT_ of energy which needs to be sent
| somewhere very quickly. Each wheel might need to dissipate
| hundreds of kW of power, simultaneously, on-demand, at any
| time in normal situations where mechanical brakes function
| fine today. This is not inexpensive.
|
| 2. Today, most EVs do not have 1 motor per wheel, which would
| be almost surely required to implement this type of system
| effectively. That's also not inexpensive and unless you can
| actually put the motor in the wheel-area you still need an
| axle to connect the motor to the wheel due to the suspension
| and steering movement, and then that axle would need to be
| able to sustain these braking forces.
|
| It surely could be done from an engineering point of view
| today, it's just going to add tremendous cost over using
| conventional mechanical brakes regardless of if those brakes
| are a traditional hydraulic type or if they're a brake by
| wire system.
| analog31 wrote:
| I suspect vibration, and the need for 4 motors instead of 1.
| I'll bet it'll be a long time before motors are cheaper than
| brakes. Also, braking involves a lot more torque than
| accelerating or cruising.
| btbuildem wrote:
| I think having one motor per wheel is very useful in terms
| of all-wheel drive (and braking) -- being able to
| selectively apply varied amounts of power to each wheel
| depending on conditions.
|
| Not sure I'm convinced by the torque claim -- we've seen
| cars skidding / losing traction in both scenarios
| (accelerating and braking). ABS brakes were developed
| specifically to prevent that (and so was Traction Control).
|
| My experience with electric vehicles is limited to a
| Boosted longboard, so take this with a grain of sand -- but
| it seems to me that electric motors are as effective at
| braking as they are at accelerating.
| 3pt14159 wrote:
| That's an awesome idea!
|
| I'm looking forward to the day where beamed power (e.g., MASER)
| will allow us to ditch most of the batteries too, with a tow
| trailer battery pack for trips into the deep country. It makes
| no sense to me to accelerate and decelerate over a ton of
| battery pack and have to deal with so much regeneration loss
| when we could just have overhead beamers optically track
| vehicles and cut power whenever a stray bird enters the
| picture.
| bilsbie wrote:
| The government will turn off the MASERs on hot days though
| ...
| mensetmanusman wrote:
| It probably makes more sense then a huge infrastructure build
| of giant maser units that would have to be able to
| simultaneously track hundreds of vehicles on every dense
| street corner and then you would have to put up mitigation
| for all the reflective power losses going through windows
| into peoples houses.
| sbradford26 wrote:
| So a big reason why this probably wouldn't fly is that it has a
| common mode failure which is loss of power. Most EVs don't use
| permanent magnetic motors so it needs power to be able to use
| the motors for regen. So lets say the relay fails from the main
| battery pack suddenly you have no power, and no way to energize
| the coils in the motors to use them to regen. This could be
| mitigated by using permanent magnet motors but you still have
| the issue if control power is lost the vehicle cannot stop. The
| beauty of hydraulic brakes is that they work really well with
| power, but still function without it.
| Verdex wrote:
| Interestingly enough, I've had hydraulic brakes fail on me
| for two different cars (thankfully it was 20 years apart, but
| still I would have preferred that the first time was the last
| time).
|
| iirc both times it was some sort of brake fluid leak.
|
| So, while I totally agree that having motorized breaks is
| really scary, hydraulic brakes can fail as well.
| abakker wrote:
| I had _a_ brake caliper jam on my tundra. Completely frozen
| sliders on the caliper. The good news about hydraulic
| brakes is that the other circuits on the brakes still
| worked fine! I actually didn't realize the caliper was dead
| for (likely) a few months. With modern cars, each wheel is
| independent, so leaks and failures are more failsafe.
| drewzero1 wrote:
| I've also had two cars lose brake pressure. I'm very
| thankful that the cable-operated parking/emergency brake
| was functional on both cars; it saved one of them from
| going through the back wall of the garage.
|
| The cable-operated E-brake definitely doesn't stop the car
| anywhere near as well as the power-assisted hydraulic
| brakes, but having two different braking methods can be a
| literal lifesaver when one system fails. (And all systems
| fail! I'd previously had two other cars where the E-brake
| didn't work.)
| Taylor_OD wrote:
| I've never had my breaks fail on me. I also don't use the
| parking break that often. I would be so proud of myself
| if I realized what was going on, remembered that the e
| break exists, and used it before hitting the back wall of
| my garage.
|
| Good on you.
| qzw wrote:
| > I've never had my breaks fail on me.
|
| Just a friendly reminder that your car has _brakes_. When
| they break, then they will fail.
| jandrese wrote:
| When the hydraulics failed (brake line exploded) on my
| old vehicle I discovered that the cable is also attached
| to the brake pedal, so I didn't have to play games with
| the parking brake mechanism. There is a world of
| difference in braking force though, it's like pushing on
| the side of a brick building to gently encourage the
| vehicle to stop. I was lucky that I was driving a manual
| so I could also downshift to kill the speed.
| consp wrote:
| I had the engine fail (timing belt broke) and that also
| killed the hydraulics in that car, very different
| behaviour of the brakes compared to normal and you need a
| hell of a lot of pressure to stop but it still works.
| Downshifting was not an option since the engine didn't
| work anymore.
| sbradford26 wrote:
| I don't deny that there can be physical failures to the
| systems. And I also drive a hybrid currently that most of
| the time only uses the electric motor for slowing down, I
| don't find using the motor for braking scary. I personally
| see having both regen and hydraulic brakes on a vehicle a
| great step forward in redundancy and safety.
| fpoling wrote:
| Electrical slowdown in hybrids does not provide
| redundancy for emergency braking. The battery has to
| absorb like 500kWt during 1s, this is well outside what a
| small battery can do.
| sbradford26 wrote:
| Redundancy doesn't mean it will bring the car to a stop
| as quickly as hydraulic brakes, it is just another means
| to bring the car to a stop safely. From personal
| experience I could safely get my car to a stop in many
| situations without using the friction brakes at all.
| peteradio wrote:
| I see a lot of good ideas for how to get around this failure
| mode, I'll throw one more in the ring: "giant spring loaded
| spike to jab into the road"
| londons_explore wrote:
| I actually don't think that's a bad idea... Specifically,
| most cars can only brake at about 1 G, and if that's
| insufficient, they use crumple zones and airbags which
| brake at far more than 1 G.
|
| If emergency braking could use an explosive-spike-in-ground
| deceleration at say 5 G, then far more crashes would be
| survivable.
|
| I think the reason it hasn't been done are human reasons -
| users don't like the idea that jabbing the brake pedal hard
| will mean they have to pay tens of thousands of dollars to
| repave the road and replace their spike.
| bilsbie wrote:
| Maybe dedicated capacitors it's enough power for one stop? Or
| a mechanical fail safe? Just a big pad that drops down on top
| of your tires.
| sbradford26 wrote:
| Hold up capacitors definitely could extend the length of
| time the brakes would work but it would depend on what the
| power failure was and how long you need to brake. A
| mechanical fail safe just seems like a worse version of
| hydraulic brakes.
| p1mrx wrote:
| Maybe the capacitors could store enough energy to start
| braking, and then the braking energy could recharge the
| capacitors.
| extrapickles wrote:
| That is easy to accommodate as you can design the electronics
| such that when there is no power they cause maximum braking
| force and dump energy into the braking resistors. This can be
| done completely with power taken from the motor itself and if
| it's not turning to generate power, then I would expect the
| parking brake system to engage, eg: a spring defaults it to
| "On" and power is used to keep it disengaged.
| linkdink wrote:
| Slamming on the breaks is not a solution. Part of what
| makes hydraulic breaks safe without power is you can still
| control the breaking force.
| extrapickles wrote:
| That would be the default of this system if the brakes
| are still able to communicate with and provide power for
| the brake pedal. Basically if the brake system lost
| external power, it would get the power needed to run via
| scavenging it from the motors. Once the vehicle came to a
| stop, it would then loose power and the parking brake
| would then engage.
|
| The slam on brakes case would only trigger if there was
| gross damage to the braking system, where you might have
| bigger things to worry about.
| linkdink wrote:
| I think you've lost sight of the initial concern that was
| raised. There's still a common-mode failure of loss of
| control power.
|
| Control power is different from actuation power, the
| latter of which is what you're addressing. And it's not
| "gross damage" because it's a common-mode failure, so you
| can't just ignore it like that.
| londons_explore wrote:
| It is trivial to derive control power from actuation
| power - at least enough for a few can-busses that run
| from each wheel to up-to-12 independent sensors on the
| brake pedal.
| linkdink wrote:
| It's trivial if you're doing an opportunistic design, but
| it's challenging to match the safety and reliability of a
| hydraulic system while beating the cost.
| extrapickles wrote:
| To lose local regen braking derived power requires a
| failure of the cars systems similar in nature to one that
| would cause loss of hydraulic fluid or air in a
| traditional braking system.
|
| Edit: made more concise.
| linkdink wrote:
| I see what you're saying now
| SketchySeaBeast wrote:
| So rather than coasting to the shoulder when you run out of
| gas your tires immediately slam full on coming to a
| screeching, uncontrolled stop in the middle of the highway?
| extrapickles wrote:
| Nope. If your car lost power for whatever reason, the
| system would scavenge power from the inertia of the car
| and the brakes would still operate as they do when the
| car is operating nominally. The 1-10w needed to run the
| braking system is a rounding error in comparison to the
| 4-10kW of wind/rolling resistance at freeway speeds.
| SketchySeaBeast wrote:
| 1-10W will run the entire braking system, from foot pedal
| through computer systems to activating the breaking
| resistance?
| noduerme wrote:
| hah. I didn't see this before I wrote my comment. Really
| makes you wonder about this common SWE fantasy of mew
| ways to turn cars into big electronic touch screen
| devices, whether the people dreaming these ideas up have
| ever actually driven a car.
| NullPrefix wrote:
| >That is easy to accommodate as you can design the
| electronics such that when there is no power they cause
| maximum braking force and dump energy into the braking
| resistors
|
| This is still uncontrollable failure. What if the car is in
| the third lane doing enough speed and there's some cars
| behind? I assume no ABS, because ABS can't work with locked
| up brakes. This means no steering, just skidding whatever
| way.
| extrapickles wrote:
| Having no power would be hard as the brake system can
| easily generate power to operate itself if the vehicle is
| moving (and if its not moving that is what the parking
| brake is for). This is more of a scenario that occurs
| when there is a catastrophic failure in the braking
| system, such as the motor control electronics getting
| damaged.
| noduerme wrote:
| So fallback in the case of power loss is you don't come
| coasting to a stop, your car just suddenly and unexpectedly
| slams on the brakes? What's it do for recovery, accelerate
| into the car in front of you?
| sbradford26 wrote:
| This can only be done with permanent magnetic motors which
| is not the norm for EVs for many reasons. In a non
| permanent magnetic motor on loss of power there is no
| energy to dump into braking resistors since the motor is
| not causing any resistance because the coils have been de-
| energized.
| extrapickles wrote:
| Most EVs have permanent magnet motors of some flavor
| right now (some have both a PM motor and a pure
| induction). I would assume that if you were having the
| motor be the primary braking system, and it was
| induction, there would be a tiny cheap magnet installed
| in it to generate bootstrap power to prevent exactly this
| scenario.
| londons_explore wrote:
| An even simpler design is to assume that the car can only
| start moving when there is power. If there is a loss of
| power while moving, then you can use the energy in the HV
| capacitors in the inverters to make a bootstrap field.
| That can be maintained till the car stops (and the user
| still has control of when/how much to brake). When the
| car comes to a halt, the parking brake is applied, and it
| won't move again till repaired.
|
| All of that can be done with software-only - no hardware
| changes needed.
| spaetzleesser wrote:
| Parking brakes are pretty useless to slow down a car from
| any decent speed.
| buildsjets wrote:
| This is entirely dependent on how your vehicle is
| designed. Pulling the electronic parking brake in my car
| (Audi S4) at a decent speed applies maximum braking
| effort to all 4 wheels simultaneously. It'll practically
| pop your eyeballs out.
| spaetzleesser wrote:
| Interesting. Although if that brake is electronic you
| can't really use it as backup in case something goes
| wrong with the car's computer systems.
| HeyLaughingBoy wrote:
| Define "decent." I lost all hydraulic brakes on my 87
| Toyota pickup due to a hole in a brake line and I had to
| drive it to the repair shop using only the cable-operated
| handbrake. Granted, I didn't go on the interstate, but at
| some point I was still doing 35-40mph.
|
| Having a stick shift definitely helped, though.
| throwaway0a5e wrote:
| Letting the driver decide whether to coast or brake is far
| safer than making the decision for them.
| spaetzleesser wrote:
| Good point. Feels a little like airplanes where at some point
| it was decided that mechanical backup is not needed for fly
| by wire.
| sbradford26 wrote:
| So a fly by wire aircraft might not have physical cable
| moving surfaces, but most of them have a backup mode that
| relies basically entirely off of physical switches and
| direct communication with the surfaces. Those modes are
| only used in extreme emergencies but they are still
| designed into the system. Also what works in airplanes
| doesn't always translate to cars. Aircraft have rigorous
| maintenance requirements, while cars leave the manufacturer
| and might not have any sort of inspection or maintenance
| done for 20 years.
| crgwbr wrote:
| Interesting. Is there no way to design the circuitry so that
| when given no input, it defaults to a fully brakes-engaged
| mode? I've only worked with PM motors, so I know how that
| sort of h-bridge could be designed, but my knowledge of non-
| PM motors is fuzzy at best.
| Bilal_io wrote:
| If you're driving 75 mph and one or more motors suddenly
| lose power and it fully brakes, that's a certain death in
| my opinion.
| mellavora wrote:
| Well, it is certainly a very shaky proposition, and the
| car will probably be a total loss.
|
| But there are ways you could walk away from this.
|
| You see some pretty crazy crash survivals in race
| driving, for example.
|
| And I remember stories from a few years ago, when Ford
| had a recall on F150 tires because they tended to blow
| out at highway speeds, with an effect similar to full
| wheel lockup-- yes, people died, but others didn't.
|
| life == hope
| notatoad wrote:
| are people under the impression that when you're driving
| down the highway at 75mph, there isn't already a hundred
| ways you could die?
| progman32 wrote:
| I mean, now we have 101 ways, and not all those ways are
| equally likely...
| steveBK123 wrote:
| I'd imagine this was introduce adverse failure modes like -
| slamming to a stop without warning within seconds on the
| highway if power is lost, rather than coasting to a halt...
| and then being untowwable as the car can't be put into
| neutral.
|
| Tesla's that lose battery are already a challenge to tow as
| the parking brake cannot be disengaged without power.
| sbradford26 wrote:
| So looking into it a bit there are what is called Eddy
| current brakes. In the section of disk eddy current brakes
| it talks about the power tool implementation where there is
| just a metal disk and the magnetics are pulled away from
| the disk when the device is powered on and passively return
| to the disk when power is removed. Something like that
| could work, but I am unsure of the size of magnets or disks
| necessary to adequately stop a vehicle. Most likely you
| could also add a normally closed relay hooking the motor to
| a resistor load. So when power is applied the resistor load
| is disconnected, and in a loss of power event the motor is
| directly tied to the resistor load.
|
| https://en.wikipedia.org/wiki/Eddy_current_brake
| hoosieree wrote:
| Eddy currents develop in proportion to the speed of the
| moving magnetic field. So if you used eddy currents for
| braking, it would be most effective at high speed and
| gradually have _no_ stopping power at low speed.
| sbradford26 wrote:
| That is mostly true about regenerative braking as well.
| Once you hit a certain speed the vehicle has to use some
| energy to get the motors to actually stop the vehicle.
| Usually EVs and such will just rely on the friction
| brakes for the last bit but some cars like the Bolt will
| automatically use some energy to slow the car to a stop
| so you can use do one pedal driving.
| HeyLaughingBoy wrote:
| Hmmm. So you're travelling along the interstate at night,
| you lose power and your car screeches to a stop in the
| middle of high-speed traffic and your lights are off.
|
| I would love to be present at the DFMEA (Design Failure
| Modes Effects Analysis) meeting when this came up!
| snowwrestler wrote:
| "It still kind of works without power" was an idea that kept
| hydraulic actuators in planes for a long time. But now most
| new planes are fly-by-wire (fully electric). Reliably
| stopping an electric car in an emergency should be a solvable
| problem.
| sbradford26 wrote:
| So the fly by wire just means it is digital control to the
| hydraulic actuator instead of a physical cable running from
| the yoke or something to the actuator. They have not gotten
| rid of hydraulic actuators yet, they are working do that in
| the future but that is still a long ways out. Aircraft
| power systems also have significantly more redundancy so
| loss of control power is not a common mode failure due to
| have multiple dissimilar power sources.
| NegativeLatency wrote:
| It could be solved but it might not be worth it.
|
| Planes have a whole different set of expectations on their
| reliability and upkeep.
|
| For example I don't think people would be excited about an
| electric car with an aux power unit.
| HPsquared wrote:
| They already have an auxiliary power unit of sorts: the
| 12V battery.
| Kon-Peki wrote:
| The air brakes used on heavy vehicles (semi trucks, etc)
| have a very simple fail-safe. You need power to _not
| brake_. I.E. Air pressure is used to disengage the
| brakes. If you lose power /air pressure, the brakes
| engage and are stuck engaged.
| theluketaylor wrote:
| Hub motors will be common on scooters and other small electric
| vehicles, but it will never make sense on full sized cars. The
| size of motor required to move a car with the acceleration and
| speed modern traffic demands just won't work in a hub.
| Reduction gearboxes and axle-shafts already represent a pretty
| tiny fraction of the total mass of drive units on EVs and there
| are no mass savings coming on motors that will somehow get them
| into the range of acceptable unsprung weight, even axial flux
| motors.
|
| The whole industry is working on tighter integration of the
| drive unit components to reduce things like cooling circuits,
| length of high voltage cable runs, and the total mass of the
| components required to move the car. No one is working on
| splitting the motors out into the hubs.
|
| As you point out, unsprung mass is bad. Especially for
| something like a motor it's beyond bad, it's a complete killer
| of ride quality and reliability. As sprung mass the entire
| drive system can be isolated from all the knocks and
| oscillations that happen from driving around. A hub motor will
| get crashed and bashed around and have a miserable MTBF. The
| occupants will hate the car since it will have awful handling
| and hitting even moderate-sized bumps will be terribly
| unpleasant. Lighter stuff like scooters can get away with hub
| motors since there just isn't that much mass to begin with, but
| cars are huge now.
|
| Aptera is planning to use hub motors, but their car is the
| vapourist of wares and relies on being counted as a motorcycle
| under regulations. Their basic engineering just doesn't work
| when scaled to a 3500 pound car and beyond.
| sdk16420 wrote:
| Hub motors are in development for cars too, e.g.:
|
| https://lightyear.one/articles/lightyear-and-elaphe-
| develop-...
| mechanical_bear wrote:
| I love when people make broad sweeping assertions of
| impossibility, they are often proven wrong.
| extrapickles wrote:
| I could not find anything that would prevent this in my brief
| skim of FVMSS 105 (US car brake regulations). The regulations
| are mainly about the performance of the braking system (eg:
| needs to stop car 10x from 60mph in under a specific distance)
| and only care a little about the specific technique.
|
| You should see what you propose on cheap cars if motor pricing
| becomes less than the cost of regular hydraulic brakes.
|
| FVMSS 105:
| https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pd...
| Kon-Peki wrote:
| > S5.1 Service brake systems. Each vehicle must be equipped
| with a service brake system acting on all wheels.
|
| What is a "service brake"? Notice that the regulation you
| linked to includes requirements for EVs that have braking
| regeneration as a component of their "service brake".
|
| It turns out that the top-level of FVMSS [1] says that "
| _service brake_ means the primary mechanism designed to stop
| a motor vehicle. "
|
| So I think you are exactly right. There is nothing in the law
| that says you can't use a 100% brake regen system in an EV.
| It just has to work and meet the performance standards (and
| perform regen on all wheels). But I'd guess that you aren't
| going to see the traditional brake system disappear unless it
| starts getting in the way. They don't cost a lot (relative to
| the price of the car), don't weigh a lot, are really
| reliable, and work really well.
|
| [1] https://www.ecfr.gov/current/title-49/subtitle-B/chapter-
| V/p...
| jackmott wrote:
| Gearbox serves more purpose than just getting the power to the
| wheel, it also improves the efficiency of the motor and\or
| expands and optimizes the usable speed range of the motor.
|
| Also cars can stop way harder than any regen can, massive
| amounts of energy will be at play and likely any solution is
| more complex than just grabbing a rotor, which is a more direct
| way to heat dump
| lelanthran wrote:
| > Suspension and steering design is then far easier, because
| there is no axle to need to keep straight.
|
| I don't understand what you mean by this. Isn't independent
| suspension already a thing? Each wheel has independent up/down
| movement because there is no axle that remains straight
| (driveshafts are independent from each other in both FWD and
| RWD).
| VLM wrote:
| There are no up-down movements in full size cars and trucks,
| some kids toys maybe. Everything bigger moves an arm along a
| radius, which is "close" to up and down but not up and down.
|
| Tire friction usually works on a vector-like system so being
| able to move more up-down rather than along a radius means
| maybe you'd get a couple percent more friction forward and
| back if not moving a little side to side when moving up and
| down. Which sounds useless, but 5% more usable tire friction
| means an improvement in braking and cornering performance
| which either makes the car safer or could theoretically make
| it cheaper/lighter to compensate.
| mauvehaus wrote:
| > This is felt as kick-back to the driver and if it's bad enough
| can rip the wheel out of your hands. Some of you may have had
| that experience in the past.
|
| It can also break the driver's thumb, if the thumb is on the
| inside of the rim. If you're driving over rough terrain, you're
| well advised to keep your thumbs on the outside of the rim. This
| is true even at low speed. I once had to pull a car up onto a
| normal-sized curb and did so at low speed. Doing so definitely
| kicked the wheel.
| pwpw wrote:
| I was taught to do this in open-wheel racing. Thumbs stick
| straight up rather than gripping inside the wheel. And on
| bigger crashes, completely let go of the wheel as quickly as
| possible.
| techdmn wrote:
| My dad taught me that when I was learning to drive. What's
| the last thing you do before impact? Let go of the wheel.
| ComputerGuru wrote:
| And, counter-intuitively, get off the brakes! This
| returns/angles the nose of the car up, which can be the
| difference between life or death if colliding head-on into
| a larger object (like a deer).
| xkzx wrote:
| The flatness in this case is the outer surface of the aluminium
| rim. And as a rim enthusiast, I can agree that the modern
| flatness is less appealing than compared to those in the past.
| 6stringmerc wrote:
| Deep dish on the old M5 was pretty classy looking, as will the
| Dodge Charger msg wheels with the curve. It's too bad the deep
| dish got all bro-dozer crazy.
|
| I do very much enjoy watching "Kid Stance" videos on YouTube if
| you want to see a really brilliant creative guy make some
| AMAZING custom kid ride on toys...warning: addictive!
|
| https://youtu.be/-JF58phVWn0
| js2 wrote:
| I'm reading this article and the whole time I'm thinking, my 1998
| Jeep Cherokee XJ has completely flat wheels, and then I get to
| the very bottom:
|
| > [Editor's Note: Not all designers prefer dished wheels. Some
| commenters were wondering why the Jeep JK/JL Wrangler, which has
| an old-school steering box instead of a rack and pinion setup,
| has such flat wheels. As far as I know, this is largely a styling
| decision. -DT].
|
| So, it also applies the the XJ limited wheels too:
|
| https://i.ibb.co/zfHMNbB/B03-FA738-777-A-40-D6-817-F-C0785-E...
| sschueller wrote:
| OT but related to tire pressure.
|
| There was this gem [1] posted in reddit the other day and I guess
| it is partly a failure of UI and inexperience.
|
| A junior mechanic tried to fill the tires to "100%".
| https://i.redd.it/eu73w8earfn91.jpg
|
| Edit: fixed, old reddit. App doesn't make old reddit links.
|
| [1]
| https://old.reddit.com/r/Justrolledintotheshop/comments/xcdv...
| a3w wrote:
| Yes, but more then that pressure is okay for just standing
| around, says the reddit thread. Also, why not old.reddit?
|
| Are the official consumption ratings not based on this kind of
| overinflation, removing all seats but the driver's?
|
| So everyone is expected to do both these things by the car
| manufacturer, if that is 'realistic use'. /s
| ed312 wrote:
| As an i.reddit mobile user, it retains the old iphone/mobile
| optimized css of reddit. There are actual html buttons with
| minimal js nonsense and not a to of a useless whitespace. On
| desktop I'm a fervent old.reddit user and sincerely hope they
| don't deprecate the, (imo better, more info dense), style.
| jimjimjim wrote:
| The Autopian is a great car site. It was set up by some Jalopnik
| writers (david tracy and jason torchinsky). As well as "normal"
| car articles they love techy/offbeat/unusual aspects of cars and
| aren't afraid to publish it.
| Theodores wrote:
| The Autopian has single-handedly revived my interest in blogs.
| Great content and thanks for the back story!
| 1letterunixname wrote:
| I have a 1985 VW Vanagon camper. Mechanically, it's a POS with
| 99.9% NLA parts. It has 16" truck tires. Before that, it had
| properly weight-rated 14" trailer tires (the owner before had
| under-spec, unsafe _passenger car_ tires on it.) The 16 " are
| much easier to find and cheaper than the 14". Geometry-wise, the
| OD isn't excessively different that before because it's a
| massive, strong "pillow" between surfaces and the OD of rim. It's
| when you get to the point where you can't hop a curb at low speed
| without worrying about wrecking the rims that there's a problem
| with low profile tires. There always exists a high enough speed
| over a large enough obstacle that will cause mechanical damage to
| rims. If you want to drive a super car with perfect aerodynamics
| everyday, don't use driveways with any incline to them, don't get
| near to curbs, and don't drive anywhere with potholes.
|
| The challenge is how much optimization for efficiency vs.
| durability vs. cost manufacturers want to or are ordered to
| sacrifice.
| throwaway0a5e wrote:
| The kind of person who doesn't understand that trailer tires
| have some pretty substantial tradeoffs in car use is not going
| to be loading their classic van heavily enough and then driving
| it fast enough to have issues with some random car tires that
| don't match the OEM weight rating.
| burlesona wrote:
| What a great article! The world is absolutely full of things that
| are carefully designed around very real engineering constraints
| that almost none of us know about or ever notice. I always
| appreciate when a writer can bring me into a new world that I
| didn't know anything about and show me the care and attention to
| detail that I would otherwise have never seen.
| culopatin wrote:
| I'm going through this experiment myself. I have some et20 (+20mm
| offset wheels) in a car that had 45mm offset wheels from the
| factory. Meaning the wheel center is 25mm further out than stock.
| However, the new wheel is also wider, so is not all on one side.
|
| The steering is definitely different, especially because I also
| have tires that are 3 inches wider than the factory ones. The car
| is harder to keep straight if the ground is uneven because it
| wants to pull in all sorts of directions. I also don't like how
| at full lock the outer wheel drags on the ground. But at this
| width the closest I can get is an offset of +35mm, any higher and
| the wheel touches the control arm, and at 40 it would probably
| hit the springs.
|
| Talking to some track guys seems like they are still faster with
| a wider track than with lower scrub and told me to not worry
| about it, but I still have my concerns.
| vishnugupta wrote:
| Given my OCD this drives me nuts because I can't look at a wheel
| to get a sense if it's low on air pressure anymore. I always get
| nervous thinking it's gone flat and needs fixing.
| rob74 wrote:
| The "flat" in this article was referring to the hub side (i.e.
| where a hubcap would be if there was one), not the surface that
| meets the road.
| yason wrote:
| The timeline of this development exceeds the timeline of my own
| experiences since the 90's.
|
| I've always driven cars with rack and pinion steering while
| wheels went from something like a typical 185-65x15 to 245-40x18.
| So, wheels are larger and the profile is much smaller (more rim
| and less rubber between the car and the road).
|
| Higher power warrants bigger brakes and bigger brakes warrants
| larger rims but for the average car rims have grown way
| oversized. Many cars have the space to take rims that are 2-3
| inches smaller than what comes as standard.
|
| My anecdotal and average empirical results is that cars with wide
| rims and little rubber mostly seem to reduce comfort, increase
| noise, and make the steering very susceptible to unevenness,
| slopes and grooves of roads and layers of snow and ice and thus
| requiring constant steering response from the driver. I've had
| both kinds and the difference is huge, and exaggerated by bad
| road conditions that we find on our roads. On my older vehicles
| with a higher and narrower tyre profile I barely have to steer at
| all but just keep my hand relaxed on the wheel while the car
| ploughs pretty much through whatever in a direct line. Of course,
| I keep the wheel geometry of all my cars well-aligned so they
| shouldn't wander around.
| lloeki wrote:
| My car is on 225/40/18, has no floating behaviour, and just the
| right amount of feedback still to feel what happens on the
| front wheels, whether it's wheel placement, movement,
| gripping/slipping... It's an absolute joy to drive, whether on
| long journeys or spiritedly.
|
| > just keep my hand relaxed on the wheel while the car ploughs
| pretty much through whatever in a direct line
|
| I would avoid small potholes still but that's basically my
| feeling on that car. I did slightly bend a rim once when
| running through a pothole I did not see, and the car ploughed
| through as described.
|
| I recall reading an article a couple of months ago about
| steering, feedback, and suspension geometry design. It rang
| very true to my subjective experience that many car suspensions
| are designed for "comfort" (vs "sporty"), which results in a
| lack of relevant direct feedback, which makes the car uneven
| and floaty, like you're somehow disconnected from the road, and
| still suffer from bumpiness as you have to rely on indirect
| cues to compensate, which makes for increased latency and
| overcorrection.
|
| I wish I could find this article again, IIRC it all comes down
| to one angle/offset, which you can't really fix by tuning
| geometry because it's basically baked in the suspension design.
|
| EDIT: it's related to that one[0], but was more detailed
| regarding that part:
|
| > To make matters worse, the suspension geometry often further
| compromises steering feel in favor of things like putting less
| load into tie-rods
|
| [0]: https://arstechnica.com/cars/2022/01/new-cars-have-lost-
| thei...
| throwaway0a5e wrote:
| It's the wide tire contact patch and not the big rims that are
| causing most of the problems you describe. This is typically
| papered over with tons of steering assist and geometry that
| favors minimal feedback in order to alleviate the propensity of
| wide tires to be greatly impacted by changes in road shape.
| This steering solution feels numb and disconnected from the
| road which is a common complaint with modern cars. The wide
| tires that are at the root of the problem are a key element of
| modern car performance so they're not going anywhere.
|
| Additionally, if you move the wheel surface far enough from the
| center of the tire you can get more room for wheel bearing and
| axle shaft hardware without increasing the size of the wheel
| bolt circle and bore though this isn't a big consideration in a
| lot of applications as there is ample space either way.
| pierrebai wrote:
| One question I've had: why are car brakes inside the wheel at
| all? Is it only ease of servicing? Putting the brake disks on the
| shaft before the suspension would make wheels lighter and allow
| positioning the kingpin much further out.
|
| I tried to google for an explanation, but only found hits about
| brakes problems.
| jcampbell1 wrote:
| It is called inboard brakes. I think there is a chance they
| make a comeback with electric cars because the braking system
| can be zero maintenance due to regen and the half shafts are
| already very strong due to the powerful motors.
| whalesalad wrote:
| I had the opportunity to design my own set of wheels with a
| friend for my Mustang GT. I put a thread together with photos of
| the process from start to finish, it was a lot of fun. I don't
| have the Mustang anymore, but the wheels are stacked in my garage
| awaiting a future project.
| https://www.mustang6g.com/forums/threads/arcane-stellar---a-...
| fipar wrote:
| Those are amazing, thanks for sharing!
|
| Also, the color on those wheels makes me think of a 90s Impreza
| (paint job in blue, please!).
| mechanical_bear wrote:
| What sort of pricing for something like this?
| whalesalad wrote:
| Retail for a set like this would be in the $5-6k ballpark,
| but I am not entirely sure as the market has evolved since
| then.
| londons_explore wrote:
| TL;DR: Wheels contain the brakes, so they need space inside for
| the brakes. Just inside the wheel is part of the steering pivot
| mechanism. Constraints around the optimal design of these systems
| prevent the classic 'domed' wheel construction.
| tobyhinloopen wrote:
| To get more money repairing rim damage, obviously
| throwaway0a5e wrote:
| The kind of people who get rims repaired rather than just
| buying new (no doubt based on some hand-wavy BS about safety
| from someone who makes a margin on the rims they sell) don't
| buy new rims.
| baxuz wrote:
| I'm usually a huge fan of engineering articles but this one isn't
| really accessible.
| Neil44 wrote:
| Some cars have a virtual ball joint on the bottom of the hub to
| get around the 'the brakes are in the way' issue. Two separate
| arms with two more inboard ball joints act the same as one arm
| with the joint much further out.
|
| https://en.m.wikipedia.org/wiki/Dual_ball_joint_suspension
| LeifCarrotson wrote:
| That article uses the same words, but I needed to see a drawing
| to understand how it works. This video was useful:
|
| https://youtu.be/I1EiR9Axfwg?t=50
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