Well, I did say that I would start to "contribute" to the forums with something useful. I did some research with Tires and Contact patches. My main goal was to find out if wider tires give you better traction. Ina short summary, YES but it is benefaction for cornering. This was written from an other post on another forum but I thought I would share the info. Most of you might know this already but this forums also has some newcomers to the racing scene.



The answer to the question: Are wider tires better depends upon whether the question concerns lateral (cornering) or longitudinal traction (straight line). I am going to assume the question concerns lateral traction. Generally speaking, wider tires have a contact patch shape that is more laterally oriented (east to west) than narrower tires which usually have a contact patch shape that is longitudinally oriented (north to south) - assuming equal outer tire diameters. If the line of action of the tractive force is in the same direction as the general orientation of the contact patch shape, more efficient traction will result. Why should this be so?

Well it turns out that a tire’s dynamic coefficient of friction depends upon a multitude of things (one of which is slip angle) but the most basic is keeping the rubber on the road. Lateral traction is the primary ‘player’ when cornering. Under cornering loads, tall and skinny tires tend to pick up their inside shoulders due to their taller sidewalls bending under the rim (when loaded, the tire displaces laterally underneath the rim). When tall and skinny tires pick up their inside shoulders (under cornering loads) their contact patch becomes conical in shape. A conical shaped contact patch is not efficient for lateral traction due to an uneven pressure distribution (think over loaded shoulder). Because wider tires with shorter sidewalls tend to be stiffer, and consequently require smaller slip angles, they start out with a contact patch shape that is wider. A wider contact patch is more stable under lateral loads (think wide column base) and so wide tires don’t tend to pick up their inside shoulders as easily as tall and skinny tires.

Moreover, a tire’s dynamic coefficient of friction depends upon slip angle. At large slip angles the coefficient drops off due to large tread compound sheer, tearing and sliding of the tread blocks induced by the road surface aggregate. Dynamic coefficient of friction is not the same as Coulomb’s friction studied in High School Physics (non-deformable bodies). In a handling situation (lateral transients) a wide tire will keep more rubber on the road surface (as the suspension gains camber) and be better able to maintain an even pressure distribution within its contact patch due to its wider footprint, stiffer, shorter sidewalls, wider belts and smaller operational slip angle regime. As a group wider ‘performance’ tires with short sidewalls usually have compounds that provide higher levels of dry and wet grip than “Mom and Pop” touring tires. But that’s another story.

For the best longitudinal traction, the contact patch needs to be long – like a tank track."


Here is a dissection of the above statements

In the 1st paragraph the guy is saying that if your contact patch is a rectangular shape you want the long sides of the rectangle going in the same direction as the car's acceleration. Thus if going forward you want the long sides of the rectanglar contact patch going fore/aft and if you are cornering you want the long sides of the rectangle going cross car. He also states that he will address traction from a cornering standpoint instead of a straight line standpoint.

2nd paragraph the guy is saying that wider is better since a wider tire will hold it's shape better in turns. He mentions picking up the inside shoulder but in the real race world most of that is tuned out with static negative camber so that when you are actually turning the corner the tire is flat to the road. Also tire pressure is increased to reduce/eliminate sidewall flex in the real race world.

3rd paragraph the guy is saying that if you turn the wheel a great deal compared to the direction you plan to go then your traction is decreased due to the large slip angle. That's why good drivers make smooth inputs to the steering wheel. Jerking the wheel causes large slip angles and reduced traction. In this paragraph he's also saying that a wider tire has a larger contact patch and thus provides more traction.

So basically the guy is saying wider is better. Of course we already knew that.

The last paragraph the guy is saying for straight line you want the long sides of the rectangle going fore/aft for the best results. To get a larger contact patch in the fore/aft direction you would need to get tires in a larger diameter. Thus 36in diameter tires would be better than 12in diameter tires. That's why slicks have such large diameters. Of course if you can't go to larger diameter tires you can still increase traction by going wider. That's why slicks are also very wide. Going wider still increases the contact patch and gives you more traction. (Note larger diameter tires also changes your effective gear ratio) (Also note that you can get larger diameter wheels without changing the diameter of the tires by using a lower aspect ratio on the new tires.)

So in a few words...for cornering it's best to increase your contact patch by going an inch wider than it is to increase the contact patch an inch fore/aft by going to a larger diameter tire. (Note going from a 16in diameter tire to a 17in diameter tire only adds a fraction of an inch to your fore/aft contact patch)..... for straight line it's best to increase the contact patch an inch fore/aft than it is from side/side. In all cases increasing the contact patch will increase your dry traction.