Mr.E.G.

im glad you asked.

this tricky to explain so plase bare with me...

your tire with the weight of your car on it is not completely round. the bottom part that is squished is flat and we know this area as the contact patch. that much is obvious.

your tires get hot as the rubber is asked to stretch and change shape. just like if you were to bend a paper clip back and forth. the section where the bending occurs gets rather warm.

as your tires rubber transitions from its normal round shape to the flattened shape of the contact patch and then back again the same effect is produced and the tire gets hot in that section.

as that section of the tire rolls back around, it cools until that section becomes the contact patch yet again. so each point on your tires tread will continuously heat up and cool down, over and over.

tires have an operating temperature. too cold and they arnt sticky, too hot and they arnt sticky (this is when they get "greasy" as you may have heard the term used).

so it would appear obvious that the less time your tire is in the transition from being round to being flat, the easier it is to maintain normal operating temperature.

now you could use a tire with a huge diameter which would mean that each point on the tire would spend more time between these cycles, but thats only practical to a certain point.

so here's the answer to your question:

if you use wider tires and the contact patch changes shape from a long narrow contact patch to a short wide contact patch (which we have already established will happen given the pressure and the wieght of the vehicle stays the same) then the tire spends more time cooling while still laying down the same size foot print. in other words the tire works more efficiently and greater levels of grip occur, or more specifically, you are allowing the tire to reach its potential grip more so than if its operating inefficiently.

now, there are other reasons why wider tires can effect handling, but keep in mind that handling and grip arnt necessarily the same thing. wider tires can change the track of the vehicle which will assist in wieght transfer, etc. so on and so forth.

tof

I think the observation about a constant contact patch might apply in theory and maybe to baloons but not to tires in the real world. Be fun to do some footprint measurements. Anybody got their stock rims/tires laying around along with a+1 or +2 rim and tire set? (Or maybe easier...a link to some documentation on such a comparison?)

Wide tires DO NOT necessarily outperform narrower tires in the wet. The issue is evacuating the water from the contact patch and wider tires (if in fact the footprint is bigger) have to evacuate more. So they will need a more agressive tread to avoid threshold hydroplaning.

Vitt

When you get new tires also keep in mind that the same advertised tire sizes differ in actual width depending on the tire and the manufacturers.

For example, I read some info on this forum that the contact patch of the Bridgestone SO2 size 225 is almost as wide as other manufacturer's size 245. So if someone with an AP1 went from using 225 SO2's in the rear to another brand, they may need to get something a little wider to avoid oversteer.

vtec9

well, there's a difference between a wet road, and a road with standing water and or a lot of rain.