Tyre height normal <-> low profile

[AnthonyG]

In recent years, low profile tyres start to appear more and more on cars, a lot of people believe that it has better performance.
However, reality often proves them wrong.
A BMW M3 with 18" wheels is faster trough corners than one with 19" wheels. (both stock)

I'm trying to find a sound explenation as to why this is, since on the internet you only find "low profile tyres have fewer deformation and handle better" or "18" wheels were proven faster in a test", no real explenation.

I think the explenation has something to do with the folowing
*a lower profile tyre responds a bit quicker to the driver imput hence giving the illusion that it handles better

*while turning the front tyre contact patch reduces more with a low profile tyre than a normal profile tyre.

*the frequency of the tyre (the lateral moving when loosing grip) is much better manageable with a normal profile tyre, since the tyre absorbs more energy and is easier on the suspension, making the car more stable on the limit.

*a low profile tyre only would improve the handling if the surface were 100% flat, which, in real life never happens.

Please enlighten me.
Also, is there something as an ideal tyre height, given a certain sidewall stifness en width?

[Jersey Tom]

I'd say one of the main driving forces behind low profile tire packages is purely marketing / visual appeal... not so much to do with actual engineering and performance.

[Greg Locock]

Yes it is a fashion thing. In order to get the really low profile tires to ride anywhere near acceptably they have to reduce the sidewall stiffness, thereby destroying the main advantage of a low profile tire. Obviously there is an optimum sidewall height for a given tread width and OD, for a given construction, and my guess is that for a BMW 5 series it is an AR somewhat more than 40. Of course the additional gotcha with BMW production tires is that they are run-flats, so maybe new rules apply.

Looking at Flattrac data for 16 17 18 and 19" tires by the same manufacturer for the same car it is hard to see why, but it so happens the 17 and 18 suit the car best, subjectively the 18s win. That may well be because that's the tire that was mainly used during the development process.

[flynfrog]

long story short. Added sidewall allows for more contact patch outside of optimal camber angle to a point.

[Tommy Cookers]

which is why F1 didn't need correct suspension geometry in camber until about 50 years ago
does current F1 have or need it, given the current relatively non-low profile 'wobbly sidewall' tyres ??

does F1 tell us anything about the 'how low can we go' profile ?
or is it a fashion bound up with having big brakes for some special purposes ?

[Greg Locock]

long story short. Added sidewall allows for more contact patch outside of optimal camber angle to a point.

Which of course given BMW's curious choice of front suspension is actually rather important.

[Jersey Tom]

long story short. Added sidewall allows for more contact patch outside of optimal camber angle to a point.

Or alternatively, there's often no practical "optimal camber angle" for tall sidewall / heavily loaded tires. Durability limit (blistering & other failure modes) rather than performance limit. Think Red Bull demonstrated that pretty well not too long ago.

does F1 tell us anything about the 'how low can we go' profile ?

Hmm. I don't think it tells us anything new. As has been brought up in here, the whole craze for low profile tires is driven mainly from marketing. I can think of at least one example of a very well known RWD sportscar that falls into this.. and arguably suffers (performance wise) because of it. Or at the very least, paints itself into a box. But then again the majority of these vehicles get cruised around on weekends or sit in garages, rather than being run hard at track.

[DiogoBrand]

IMO there's a limit for everything. You don't want a tyre that's basically an unpredictable balloon, as many would argue the current F1 tyres are, but also don't want a tyre that's just a lick of paint over an overly large wheel, which won't be very good at absorbing imperfections and that sort of thing..

[bill shoe]

I don't have as much vehicle development experience as a few of the people here, but I have some.

When I was a evaluation driver I did several programs where there was a base tire of x inches diameter, and an upgrade/premium tire of X+1 inches diameter. Every time this happened, the X tire would quickly come close to the subjective targets but the X+1 tire required more work. Later rounds of testing (last 1 or 2 rounds out of 3) basically involved trying to find ways of making the X+1 tire behave like the X tire. The smaller base diameter always turned out to be a more natural fit with almost all of the subjective targets-- steering feel, ride, handling, etc.

A tire engineer explained it this way: The car doesn't change weight (significantly) between the base vs upgrade, but the upgrade tire has less air volume. Tire load capacity is proportional to the contained mass of air, so lower air volume means lower intrinsic load capacity. Air pressure can be set higher on the upgrade tire to partially offset this, but you still end up with less load reserve/margin on your upgrade tire. This tends to constrain the overall design box more tightly around the upgrade tire.

[ds.raikkonen]

This question has plagued me for a long time as well!


Vs

I believe the high sidewall Cobra used to perform really well. The one with low sidewall tyres looked better (and would've cornered better with a decent suspension set-up). But for acceleration, the low sidewall tyres would be better.

I'd say one of the main driving forces behind low profile tire packages is purely marketing / visual appeal... not so much to do with actual engineering and performance.

Won't you require bigger wheels to accommodate bigger brake discs (steel discs, not carbon)?

[Belatti]

Over here there is a silhoutte racing serie that has a 4 level ladder using basically the same cars but with power increasing from L4 (350HP) to L1 (450HP). It uses "cross ply" (non radials) with a rather high AR and has 2 tyre/wheel dimension (15" and 16").

The 15" is for the L3 and 4 and the 16" for the main and support series (that would be L1&2)

Drivers who have driven in L3 (15") and then jumped to L2 (16"), with the same power/gearbox/weight but different tyre, said that ultimate grip seems to be the same, but the higher wall tyre is noticeable more "forgiving". Put it this way: Q times are similar but race pace not...

[SameSame]

To me a tyre with a higher sidewall will be able to deform and provide a larger contact patch (especially in high load scenarios such as braking, accelerating and cornering), given a reasonable tyre pressure is used that is not too high. (Like what the teams in F1 are trying to exploit?)It would be interesting to see a a normal tyre tested against a low profile tyre (same diameters or maybe low profile 1" larger) with the normal tyre's pressure being increasingly stepped up to see at which pressure the performance cross over is (using the recommended tyre pressure for the low profile tyre).