# Friction and wide tires.

#### BenLi

I was watching the Malaysian Grand Prix, when seeing the really hugely wide tires on the F1 cars got me thinking. Theoretically, friction is a function of only the normal force and the coefficient of friction. Why is it, then, that the cars would have those wide tires?

Related Classical Physics News on Phys.org

#### Holmz

I was watching the Malaysian Grand Prix, when seeing the really hugely wide tires on the F1 cars got me thinking. Theoretically, friction is a function of only the normal force and the coefficient of friction. Why is it, then, that the cars would have those wide tires?
main reason == because they look.

And the coefficient is not constant, but goes down as the pressure (force/area) goes up.
So running the widest gets a better coefficient averaged across the tire/tyre.
But wind resistance, and inertia favor skinny wheels.

#### jack action

Gold Member
On selecting tire size, when looking for info, you can find a lot of guess work based on who knows what. Too bad tires companies and tire engineers don't talk much more.

To me, http://buildafastercar.com/node/9" [Broken] is what I think explain best, in a simple way, a very complex subject.

Last edited by a moderator:

#### Lsos

Theoretically, friction is a function of only the normal force and the coefficient of friction. Why is it, then, that the cars would have those wide tires?
The coefficient of friction is a classic example of how high school "theory" doesn't always agree with the real world.

#### jack action

Gold Member
The coefficient of friction is a classic example of how high school "theory" doesn't always agree with the real world.
The "high school" theory of friction applies to material that do not deform like wood or steel. When there is elasticity deformation like in a rubber tire, that changes stuff.

Exactly.

#### xxChrisxx

The tyres are wide because wider tyres create more lateral force per angle of slip. However they are less able to cope with linear acceleration (this is why they tend to have large radiuses as thats what helps the tyre cope with linear accelration). Combines with 13inch wheels this and getting temperatre it's what gives F1 tyres their large sidewall profile.

More on this: (will have to find links to other tyre threads) Ranger Mike will hopefully see this and link in before I have to do a big search :P

Basically wide tyres have wider shorter contact patches (as a rough rule of thumb for a given loado the contact partch size will not change). This gives lots of grip on the limit in corners, but gives a tyre that has little warning it's about to break traction.

#### Phrak

main reason == because they look.
Not. Tires are to win. Loosing doesn't look. Winning is look. Dude, you've got it backwards. Turnit around.

Last edited:

#### xxChrisxx

They are also thinking of switching to 18 inch wheels (from the 13inch) to bring the tyres more in line with sportscars. I doubt that will happen any time soon though.

It's all rumour for after bridgestone leave.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving