Why don't all cars use BMW i3 style tires?

Off Topic
21

Yeah this is what I was saying. On snowy roads thinner tyres do work better as the increased pressure exerted on the ground is needed to keep grip, but off roads, the wider tyres are better as the last thing you want is to get stuck.

For example,

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These trucks are specially designed to traverse tundra and as you can clearly see, they have specially designed wide tyres to spread out weight more evenly and thus preventing the truck from sinking in the more loose less compact snow out in the tundra. This is what I was referring to when I say travelling offroad in the snow.

As for rally cars, they tend to stick to roads so they need those thinner tyres.

Also at its most basic, friction depends on the coefficient of friction, which depends on the surface and the normal reaction force. This is also why you dont want to dig in because by digging yourself in, you increase the point of contact between the tyre and the surface thus increasing the friction massively.

22

You make a good point. I was about to say that this might be a new concept to manufacturers, meaning it’ll take 100 years or so to catch on. But when you pointed out that new trucks are featuring 22 inch rims with 40 profile tyres, it occurred to me that it’s purely aesthetics. GMC has a new trim level - AT4 - supposedly an ‘all-terrain’ type vehicle; honestly I would not trust any of these vehicles off road.

23

How about you look at the actual performance of that mighty Testarossa.
Check it against some sporty cars today, 0-100 kph, 100-0 kph. (both distance and time)
Today’s standard cars have brakes, and power, that only super cars had in the 80’s and 90’s.

And the standard weight of a large car, say a Volvo V70 compared to a first gen 850 or a 245.
The 245 starts at 1320kg, 855 at 1465 kg, V70 at 1579.
See the trend?
Edit: V90 starts at 1825 kg.

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24

Brake size. Testarossa does a 70-0 in 210ft, an e class mercedes does it in 156ft
Supercar vs family diesel sedan of the same weight.

So you KNOW this and completely ignore it as fact…so, does that mean that you also know that the rally cars you’ve posted are running racing studs, and number of studs is reglamented by FIA, and it’s the studs that are doing all the grip work, thus the car does not require wide tires in the first place, making it a very poor example?

Hell, my friend can NOT fit a wheel less than 18" on his car and it’s a diesel hatchback, I can not fit a wheel less than 17" on a 1989 BMW… do you not think that the brakes are the main idea, and the looks is secondary?

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25

Okay 1) you did not make that clear in your original post at all; 2) you only made it clear in the very last sentence of your first follow-up post; And 3) given the context of a BMW i3 it should have been apparent @phale wasn’t talking about extreme offroad conditions, more like snowy city roads; so I don’t understand what your vendetta is about here.

And yes, in that scenario you are absolutely right that surface area is your friend but for standard road cars in places that on occasion still see bare pavement in the winter, a narrow tire is better. And that’s because you can practically never mount a tire large enough for it gain the benefits you speak of. I mean really - look how many fucking tires that truck has!

Bad example? Probably. But it doesn’t change facts. See above ^^

Also, chill out a little man.

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26

Yeah, I was also under the impression that we were talking regular street cars here, you don’t really go mudding or drive over the tundra with a BMW i3, or for that instance anything else with 2wd and a minimum of ground clearance. For the slippery conditions you see with a regular car, mostly snow over pavement or gravel, wide tyres still are bad.

Also, the width of the tyres are unnecessary when it comes to how big brakes you can fit (of course, it still gives some more grip when braking as long as the road are dry), and this thread had the BMW i3 as an example, which appearantly is running 19" rims with narrow tyres, you still can fit as big brakes as you can if you are running for example 245/30R19…

And, it is not really like that it is almost the smallest possible rim that fits over the brakes that is used on every car, there is no problem mounting 15" rims on a W203 C180, still it had 16" rims, and it’s not really the only example in the world.

And yes, I agree that it is not the best example to compare with rally tyres for snow for a street car either, but as @kmBlaine says, it still doesn’t change the facts that wide tyres are bad for winter conditions.

I don’t understand what everyone is so mad about, you just have to realize that everything on a car always is a compromise, so is the rim and tyre size too…

I remember a magazine did a test of many different wheel combinations some years ago, using a mk3 VW Golf as the test vehicle, because it could take 18" rims in the wheel wells and still fit 13" rims over the brakes. Of course, they tested wider and lower profile tyres for every step up in rim size. The best compromise for everyday driving was 14" (don’t remember the width and profile but quite moderate numbers…) and a premium tyre… 18" cheap chinese rubber with much lower profile and greater width was worse in every condition than the 13" premium tyre except for slightly better handling on dry pavement, which really was no surprise.

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27

Welcome to the Automation forum lmao

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