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I was wondering today if there is a relationship between the width of a tyre and the mechanical grip it provides?

As an example if you had 2 tyres of the same diameter and compound but of differing widths would the wider tyre necessarily provide more grip? I was wondering if the increase in width would provide a lower amount of pressure on each square centimeter of contact with the road and if this would provide less traction?

In terms of simple physics F = V mu... If you double the contact area, then the pressure will halve (per mm2) so the friction per mm2 will halve. However, you have twice the area of contact patch so that cancels out the halved pressure. The conclusion is that basic friction is independent of area, it only needs vertical load and a co-coefficient. You can do whatever you want with the area from a stiletto to a surfboard, the friction force will be the same.

However life is more complex than simple physics. The most obvious point is that tyre rubber is adhesive, so if you double the area you double the amount of adhesion (gross approximation). So wide tyres do have more grip than thin tyres.

Another point is that the stiletto will dig into the surface causing interlock but that is also ignored in F = V mu

There are couple of threads on here with a lot more detail. Have a read of them and if you have question about the concepts I suggest you post in the relevant thread. (This is probably the only forum that encourages resurrection of old threads!)

The post by Ciro in this thread is seminal in f1tech (well it is in my mind) .... viewtopic.php?f=6&t=9333

There are also some other similar threads ...

viewtopic.php?f=6&t=6330
viewtopic.php?f=6&t=8371
viewtopic.php?f=6&t=7734
viewtopic.php?f=6&t=6300
viewtopic.php?f=1&t=11603&start=60
viewtopic.php?f=6&t=12180
viewtopic.php?f=11&t=10276

"Grip" is a four letter word. Surprisingly not as easy to define as one would think.

Thakyou very much for the indepth reply! i did do a quick search however i believe my terms were probably not specific enough... Thanks once again!

It helps that I remembered there were a couple of posts by Ciro on the subject, they were certainly memorable. Also look out for posts by JerseyTom.

Try searching for "tribology" or "friction"

pyrosian wrote:I was wondering today if there is a relationship between the width of a tyre and the mechanical grip it provides?

As an example if you had 2 tyres of the same diameter and compound but of differing widths would the wider tyre necessarily provide more grip? I was wondering if the increase in width would provide a lower amount of pressure on each square centimeter of contact with the road and if this would provide less traction?

Also, tires can develop a molten layer that functions as an adhesive to the road. The tire contact patch influences the failure mode, i.e. peel, shear etc.

richard_leeds wrote:It helps that I remembered there were a couple of posts by Ciro on the subject, they were certainly memorable. Also look out for posts by JerseyTom.

Try searching for "tribology" or "friction"

What happened to Ciro? His posts were fascinating...a very unique style!

I believe that with a tyre on a smooth glass surface, you will be dependent on classic "mu" friction plus adhesion, however that is xplained. But on typical tarmac, the rubber will follow the irregularites of the surface, thus creating direct horizontal forces, why a wider tyre will yield more grip than a narrow one?

volarchico wrote:

richard_leeds wrote:It helps that I remembered there were a couple of posts by Ciro on the subject, they were certainly memorable. Also look out for posts by JerseyTom.

Try searching for "tribology" or "friction"

What happened to Ciro? His posts were fascinating...a very unique style!

I believe he left due to too much fanboyism. He lives on elsewhere in the Internets.

To a first order contact patch area is equal to vertical force divided by inflation pressure. If you have a wider tyre this means that the contact patch will be shorter.

So if you go with a wider tyre but keep the load and pressure the same all things being equal you'll probably increase lateral grip, but decrease longitudinal grip.

Ben

I remember from 2009 to 2010, Bridgestone decreased the width of the fronts - so that would decrease lateral grip slightly, but actually increase longitudinal grip? For the fronts though - longitudinal grip should have minimal effect, no? Even most braking in F1 nowadays is done with trail braking rather than straight line braking - though if it's heavy braking then the initial braking phase would be straightline braking.

raymondu999 wrote:Even most braking in F1 nowadays is done with trail braking rather than straight line braking

Not sure I agree with that assessment. Drivers don't do ALL the braking in a straight line - it is trailed into the corner - but a lot of speed is shed in the initial, straight line component for most corners.

In any event - if Bridgestone made that move to help balance the cars out then so be it, it's a logical move. Also bear in mind it was a pretty substantial (IMO) mold shape change. Lot more than just "width" involved.

As mentioned above, tire width will not greatly affect the contact patch area (A=F/P) and so the contact patch shape will grow in width and shorten in length. With a wider tire (assuming same load, pressure, etc), there is much less lateral deformation at the ends of the contact patch as the tire twists in order to generate a certain slip angle. I think the first linked thread above has some great explanations of grip generation on a microscopic scale.

ubrben wrote:To a first order contact patch area is equal to vertical force divided by inflation pressure. If you have a wider tyre this means that the contact patch will be shorter.

I agree with the general thrust of this and the conclusion, but in the interest of education I think it's good to point out just how non-linear the function is that correlates contact patch area vs. vertical force and inflation pressure. It depends highly on the construction, of course. There's not a known tire that has an infinite contact patch at zero pressure, and in particular run-flats have an almost normal contact patch at zero pressure. The Avon tire company went ahead and measured contact patch size for a normal racing tire and found a surprisingly low correlation with load, as detailed here: http://www.performancesimulations.com/f ... ires-1.htm

ubrben wrote:So if you go with a wider tyre but keep the load and pressure the same all things being equal you'll probably increase lateral grip, but decrease longitudinal grip.

While this seems generally true, I'm curious about the actual cause of this effect. It seems like it must have something to do with more efficiency - you can get the same lateral deformation and force with less sliding at the tail end of the patch (to be more precise, a lower ratio of sliding vs. non-sliding portions of the patch). Do you know if this is correct? And then I'm a bit stumped for ideas about how the ratio of contact patch dimensions affects pure longitudinal grip.

When you get down to the details, there is really no such thing as the classic "mu" thing between two surfaces, at the end of the day no matter how microscopic you get it's always about forces generated by lateral contacts.

"mu" is something we have invented out of conveniancy, works reasonably well between hard surfaces, but definately not between rubber and tarmac.