[BXL4]

Is it really lateral grip that has been driving the lower and lower profile of tires over the years?

Having just seen a NASCAR racer up close, there is no way you could curb those rims so why do I have to live in fear of that?

It does look cooler but someone please tell me that there are other, better reasons for modern profiles.

[goj]

No, they look better. It's all for style

[oceanview]

The profile is in "%".
So a 345/25 tire has about the same sidewall as a 175/50.
Would it make sense to have a 345/50 on a sportscar. probably not.
It's not just for look.

Looking at our F3x series.
Three possible square setup.
225/45 on 18" (Sidewall height = 101.25 mm)
225/40 on 19" (Sidewall height = 90 mm)
225/35 on 20" (Sidewall height = 78.75 mm)
(assuming all have the same tire type and same wheel type and according tire pressure)

Which of these combo will give you a faster lap on dry road, on wet road, on snow?
I don't know. Probably someone has done a testing.
My feeling says, not the 18".

[Polo08816]

Originally Posted by oceanview

The profile is in "%".
So a 345/25 tire has about the same sidewall as a 175/50.
Would it make sense to have a 345/50 on a sportscar. probably not.
It's not just for look.

Looking at our F3x series.
Three possible square setup.
225/45 on 18" (Sidewall height = 101.25 mm)
225/40 on 19" (Sidewall height = 90 mm)
225/35 on 20" (Sidewall height = 78.75 mm)
(assuming all have the same tire type and same wheel type and according tire pressure)

Which of these combo will give you a faster lap on dry road, on wet road, on snow?
I don't know. Probably someone has done a testing.
My feeling says, not the 18".

Given the same tire width and same overall wheel/tire diameter, the 18" tire will most likely be faster and more comfortable on all surfaces. Part of the reason is that it would allow the lightest wheel which would reduce unsprung weight. It will also be less expensive to replace.

The only functional reason to have a slightly larger wheel is to fit a larger brake system.

[.BMW.]

Originally Posted by Polo08816

The only functional reason to have a slightly larger wheel is to fit a larger brake system.

+1

[fhlh]

Originally Posted by BXL4

Is it really lateral grip that has been driving the lower and lower profile of tires over the years?

Having just seen a NASCAR racer up close, there is no way you could curb those rims so why do I have to live in fear of that?

It does look cooler but someone please tell me that there are other, better reasons for modern profiles.

no increase in 'lateral grip' in an ultra low profile tire... actually less and with much less feel.
it's why I swapped from 19's to 18's...

[oceanview]

Originally Posted by Polo08816

Given the same tire width and same overall wheel/tire diameter, the 18" tire will most likely be faster and more comfortable on all surfaces. Part of the reason is that it would allow the lightest wheel which would reduce unsprung weight. It will also be less expensive to replace.

The only functional reason to have a slightly larger wheel is to fit a larger brake system.

I agree for comfort.

The 405M 18" rim is less in weight than the 405M 20" rim. But the 225/45 18" tire is heavier than the 225/35 20". In total wheel weight very small advantage for the 18" combo.
(It's almost impossible to find out because of missing weight declaration in the realoem and tire manufacturer websites. So I looked at realoem published weight but that's not 100% save)

Originally Posted by fhlh

no increase in 'lateral grip' in an ultra low profile tire... actually less and with much less feel.
it's why I swapped from 19's to 18's...

Yes that could be true. The driver possibly has a better feeling and the car is softer to handle in the "edge" area.
But that is not a measured lap time, just guessing. And so we still don't know what's faster .

[Polo08816]

Originally Posted by oceanview

I agree for comfort.

The 405M 18" rim is less in weight than the 405M 20" rim. But the 225/45 18" tire is heavier than the 225/35 20". In total wheel weight very small advantage for the 18" combo.
(It's almost impossible to find out because of missing weight declaration in the realoem and tire manufacturer websites. So I looked at realoem published weight but that's not 100% save)



Yes that could be true. The driver possibly has a better feeling and the car is softer to handle in the "edge" area.
But that is not a measured lap time, just guessing. And so we still don't know what's faster .

Actually, there's a fairly good indication that the 225/45/18 and the 225/35/20 tire weigh about the same. It's not intuitive, but apparently this is the case.

I used TireRack as a source and search for matching tires with a 225/45/18 front and 225/35/20 rear size.


Based on their current stock, only 2 tires were available in both sizes.

Michelin Pilot Super Sport - both size tires weigh 22lbs.
Sumitomo HTR ZIII - both size tires weight 25 lbs.

[JollyRodger]

On modern road cars the switch to low profile tires really is asthetic more than anything.

The sidewall if a tire impacts the responsiveness of a tire. When cornering, the wheel will flex toward the side of the tire on the outside of the turn because the sidewall is elastic. The more flex the more energy is lost in transition which in turn slows down the response of the car to steering input.

The stiffer the sidewall the less energy is used to deform it before the tires respond and change the direction of the car. Of course there is always a happy medium. You don't want to be too stiff or too soft. As the sidewall gets shorter is also gets stiffer.

But the entire design of the car's suspension comes into play here. Look an an F1 car for example, they still run 13 inch rims with a 26 or 27 inch tire diameter. But the sidewall of the car also accounts for something like 70% of the 'suspension' of an F1 car.

This can also be seen on road cars, American cars often run much larger sidewalls because they let the sidewall do much more of the suspension work. Compare a mustang or charger to a 3er for example.

And even looking at very high performance cars, 488, 911 type cars. They actually run a relatively large amount of sidewall.

[BXL4]

Let me turn the question 90 degrees. Why are rims so narrow compared to the tread? Back to my NASCAR example, not only was the sidewall relatively tall but the width of the rims were substantially narrower than the tread width.

Us that, at least on road tires, due to performance considerations?

Btw, thank you for this lively discussion. It is fun to come here to learn.

[oceanview]

Originally Posted by JollyRodger

But the entire design of the car's suspension comes into play here. Look an an F1 car for example, they still run 13 inch rims with a 26 or 27 inch tire diameter. But the sidewall of the car also accounts for something like 70% of the 'suspension' of an F1 car.

Originally Posted by BXL4

Let me turn the question 90 degrees. Why are rims so narrow compared to the tread? Back to my NASCAR example, not only was the sidewall relatively tall but the width of the rims were substantially narrower than the tread width.

You can't take any racing car as a 1:1 comparison of what's best. They are regulated in so many aspects.
In German DTC (Deutsche Tourenwagen Challange) even Audi has to drive with an all RWD car because of that's how the rules are.