Tyre width vs. performance

[Callum]

Can someone please explain to me why having wider tyres provides a better cornering force and traction because i thought that the coefficient of friction did not vary with the area of the contact patch.

I know that the new Acura LMP1 car has rear sized tyres on both the front and back giving a 7% larger contact patch at the front. So why is this an advantage?

[The Thorn]

Having more contact with the road will deliver more grip. The only reason why we won't be using tyres from 2 meters wide will be because there are regulations for the size, friction and aerodynamic drag.

Just look at drag-racing. The cars in those classes, use very big, but also very wide tyres. This is just to get more friction. Imagine a F1 car running on bike-tyres. The power distibuted to the contact-patch will just be too big.

[Scotracer]

The coefficient doesn't change but the area does

Remember the coefficient is a multiplying factor.

[Gecko]

Can someone please explain to me why having wider tyres provides a better cornering force and traction because i thought that the coefficient of friction did not vary with the area of the contact patch.

A load independent coefficient of friction is just an approximation. For more rigid materials, it's often a surprisingly good approximation. For rubber, it hardly works at all. With rubber, the higher the pressure at the contact patch, the lower the coefficient of friction.

[bill shoe]

There are two different issues here. The first is the load sensitivity of rubber, which has already been mentioned. The second is contact patch shape.

If a narrow tire and wide tire have the same air pressure and load then they have the same contact patch area. The difference is the shape of the contact patch. The narrow tire has a long narrow patch, and the wide tire has a short wide patch. This difference in contact patch shape can cause the grip difference.

A loaded tire flexes as it rotates through the contact patch. This means the slip angle between the rubber and road changes along the length of the contact patch. It turns out that a shorter contact patch has less slip variation along its length, so it's possible to keep more of the contact patch close to the optimum slip angle for generating lateral force.

To maximize grip you want 1. The biggest contact patch area possible, and 2. The shortest and widest shape possible for that contact patch area. In racing these things are usually constrained by the rules.

[Callum]

There are two different issues here. The first is the load sensitivity of rubber, which has already been mentioned. The second is contact patch shape.

If a narrow tire and wide tire have the same air pressure and load then they have the same contact patch area. The difference is the shape of the contact patch. The narrow tire has a long narrow patch, and the wide tire has a short wide patch. This difference in contact patch shape can cause the grip difference.

A loaded tire flexes as it rotates through the contact patch. This means the slip angle between the rubber and road changes along the length of the contact patch. It turns out that a shorter contact patch has less slip variation along its length, so it's possible to keep more of the contact patch close to the optimum slip angle for generating lateral force.

To maximize grip you want 1. The biggest contact patch area possible, and 2. The shortest and widest shape possible for that contact patch area. In racing these things are usually constrained by the rules.

Everything you say makes sense but could you please explain to me what slip angle is?

[Callum]

Can someone please explain to me why having wider tyres provides a better cornering force and traction because i thought that the coefficient of friction did not vary with the area of the contact patch.

A load independent coefficient of friction is just an approximation. For more rigid materials, it's often a surprisingly good approximation. For rubber, it hardly works at all. With rubber, the higher the pressure at the contact patch, the lower the coefficient of friction.

P.S you're saying that the more pressure you put on rubber the lower the CF? Does this mean there is a maximum amount of downforce you can apply to the tyre before it theoretically becomes pointless?

[PlatinumZealot]

In my mind. The tyre rubber is a material that takes load. The bigger the patch on the road... the more load it can take. The tyre has a bigger capacity for grip, less shear stress on the tyre.

Like gluing two objects together.. One bead of glue does not have the same strength as two beads of glue.. There is less shear stress on the two beads of glue because of the bigger area.

[Scotracer]

There are two different issues here. The first is the load sensitivity of rubber, which has already been mentioned. The second is contact patch shape.

If a narrow tire and wide tire have the same air pressure and load then they have the same contact patch area. The difference is the shape of the contact patch. The narrow tire has a long narrow patch, and the wide tire has a short wide patch. This difference in contact patch shape can cause the grip difference.

A loaded tire flexes as it rotates through the contact patch. This means the slip angle between the rubber and road changes along the length of the contact patch. It turns out that a shorter contact patch has less slip variation along its length, so it's possible to keep more of the contact patch close to the optimum slip angle for generating lateral force.

To maximize grip you want 1. The biggest contact patch area possible, and 2. The shortest and widest shape possible for that contact patch area. In racing these things are usually constrained by the rules.

Everything you say makes sense but could you please explain to me what slip angle is?

http://en.wikipedia.org/wiki/Slip_angle

And yes there will be a point where more downforce results in less grip, overall.

[xpensive]

Bridgestone's diffent tyre designations, "supersoft", "soft", "medium" and so on are confusing me to some extent.

Do said designations mean anything quantifyable in "shore" or something, or do properties change from race to race?

[Jersey Tom]

Very loose terminology encompassing hardness, grip level, and wear. I'd imagine the actual "soft" compound formulation varies from track to track.. but then again it's also possible they do use the same one at multiple tracks now that it's a spec tire.

Some folks like to use durometer hardness as an indicator for grip but it doesn't really mean anything by itself. The term has just been around.

You can have hard compounds with more grip than soft ones...

[xpensive]

Well JT, now you got me completely confused. Thank's, I guess.

[RacingManiac]

There are two different issues here. The first is the load sensitivity of rubber, which has already been mentioned. The second is contact patch shape.

If a narrow tire and wide tire have the same air pressure and load then they have the same contact patch area. The difference is the shape of the contact patch. The narrow tire has a long narrow patch, and the wide tire has a short wide patch. This difference in contact patch shape can cause the grip difference.

A loaded tire flexes as it rotates through the contact patch. This means the slip angle between the rubber and road changes along the length of the contact patch. It turns out that a shorter contact patch has less slip variation along its length, so it's possible to keep more of the contact patch close to the optimum slip angle for generating lateral force.

To maximize grip you want 1. The biggest contact patch area possible, and 2. The shortest and widest shape possible for that contact patch area. In racing these things are usually constrained by the rules.

To add to this, wider tire of the same construction will have stiffer rate, which will allow you to run less pressure vs the soft tire to get the same wheel rate. At which point you will have more contact patch area.

[xpensive]

But again JT, is Bridgestone continously developing the tyres, meaning next race's "softs" will not be the same?

[RacingManiac]

I thought the whole deal since last 2 years is that BS will only make 4 types of tires for all the tracks. And they pick the 2 they think will work the best out of the 4 available type to each race...so I am assuming the design of the tires are fixed...