[Lotus Fury]

Ok, time to show off my true dorkiness.

As we can observe, tires that are equal in compound but are not equal in size handle differently. Wider tired seem to be able to provide more friction than tires that are of a smaller width. One would assume that the wider tire has more friction.

According to the equation for friction the surface area of objects does not play a part in determining the absolute amount of friction that is created.

Friction = force * Coeffecient of friction. Friction Formula

Friction causes waste in the form of sound and heat. Friction and Heat. Heat dissipation is based on surface area as well as the thermal transfer coefficient. Based on this one would be able to show that a skinnier tire will heat up faster and be less able to dissipate heat. And with heat the structure of the rubber compound will, in general, weaken and with it the ability to better mold it self to the road surface, or if too much, the inability to keep its structure enough and then have rubber come off and cause it to handle worse (like doing a burnout too long).

So where are we at? Is the only reason for wider tires to handle better heat? Anyone out there know alot about tires and such?

 

[Stan]

Complex subject. But basically the friction formula relates to surfaces that do not comply to the other surface. Rubber can both adhere to other things and also conform to the shape of other things. This allows it to create grip. This grip tends to be greatest in the direction that the tire contact patch has the greatest dimension. So for cornering, this would be width. For a given corner of a car and basic tire size and inflation pressure the contact patch stays the same even if you make the tire wider. Because as it gets wider it gets less long. Since the tires hold the car up using the pressurized air contained within them.

 

[Lotus Fury]

Yeah, that's the thing it's really damn complex. That's sort of why I want to know more, it's interesting in a very nerdy way.

In general the contact patch for a sports cars is wider but shorter, as you said, but with a truck it's longer but skinnier (taller, thinner tire). I wonder what are the advantages of each? With heat the structural integrety would go down and the rubber would mold itself more to the road surface (small hills and valleys) and create a more subtantial contact patch.

So now we're also talking about cohesion (sticking to itself) and adhesion (sticking to other things). So heat would also affect this, maybe more heat less cohesive but more adhesive? (It will fall apart and stick to other surfaces)

 

[rtking]

Sorry Lotus Fury... wrong friction formula. The formula you have might apply to an eraser on paper, but you want rolling friction As such, here is the Rolling Friction Formula

The thinner tire will have a smaller contact patch and, as such, have a smaller area to deform and mold to the road surface. Thus it will generate less lateral grip than a larger tire due to deformation of the tire (contact patch) which is correlated to tire width.

As for longitudinal grip, we have to consider the vectoral forces in place on a tire. If the thinner tire (with softer sidewall and less air pressure) can deform to create a long but thinner contact patch, then it will have greater grip in the moving forward (force vector moving toward the rear of the vehicle.) A wide tire with stiff sidewalls and high air pressure provides a smaller, but wider, contact patch. Therefore it will provide good lateral grip, but will not have an equal longitudinal grip. (Hence why drag racers drop tire pressures in the rear tire... to effectively allow the rear tires' sidewall to deform and provide a larger longitudinal contact patch to allow greater forward propulsion.) The reason for higher inflation pressure in sports cars is that it allows for much more consistency during transient maneuvers. Today's tire manufacturers also construct tires to distribute lateral loads across the face of the tread, (radial vs. bias ply tires) so having higher tire pressures actually allows the tire engineering to work properly to maintain maximum lateral adhesion.

Bob

 

[Stan]

Pick up Haney's book on tires - it's excellent. Actually tires generated forces in at least three ways.

http://www.insideracingtechnology.com/booktiredescrptn.htm

 

[Lotus Fury]

Sorry Lotus Fury... wrong friction formula.
Bob

DAMN SCIENCE and all it's formulas!!! Can't everything just be summed up in one Unified Theory??? -eek-

 

[Lotus Fury]

Pick up Haney's book on tires - it's excellent. Actually tires generated forces in at least three ways.

http://www.insideracingtechnology.com/booktiredescrptn.htm

Looks like a winner to me:

The way rubber interacts with a surface to produce friction forces is so complex as to deserve the entirety of Chapter 3, Rubber Friction. The viscoelasticity of rubber dominates its friction characteristics. You'll learn about rubber's sensitivity to temperature, sliding speed, surface texture, and vertical loading. Discover the real reason why there's more grip off-line in the rain.

EDIT: Read the link - it's actually really informantive. I'm getting this book.

 

[rtking]

Unified Theory? No way... if we did it, then all science would do it... and it would be... ANARCHY! ANARCHY I TELL YOU!!!

Sorry... here's another formula to help explain deformation specifically for automotive tires. Rolling Friction Formula for Automotive Application

 

[Lotus Fury]

Unified Theory? No way... if we did it, then all science would do it... and it would be... ANARCHY! ANARCHY I TELL YOU!!!

Wouldn't that be Chaos Theory?