Thumbs up!

 

still dont get it
i need pictures

on a side note .. am i the only one that gets excited like a school girl when it comes to talking about tires/suspension/brakes ?

 

Maybe this will help.

 

ok now i get it.
so with that same logic, a 305 30 19 would have more contact patch than a 295 30 18 right ?

 

Assuming the car weighs the same and your running the same air pressure, the area doesn't increase, only the shape changes. The wider tire will give you a wider but shorter contact patch shape resulting in more cornering traction. There will be no gain in straight line traction.

Later, Steve

 

ok now i think i get it (again)
as long as the weight dynamics of the car stays the same, the contact patch size will stay the same ?

 

Yes indeedy

The footprint is the same size - but it's a different shape

The shape of the footprint has an impact on the grip levels that are possible

I'll try and write something a little more in depth, but easy to follow, over the next day or two - assuming SJ doesn't beat me to it

Steve, if I write something up can I use your picture?

 

ok now my mind is working at 100mph.
is the reason why formula 1 cars handle so great ebcause of teh downforce adding a crazy amount of "load" on the tires that far surpas the actual weight of an f1 car, thus giving it more contact area, thus giving it more grip, thus proving, for a minute that i might be too smart for my own good ?

 

Wow, I would have never believed this without the pictures. You learn something everyday. Thanks.

 

Downforce adds weight, increasing the contact patch. Decreasing tire pressure also increases the contact patch. Tire sidewall stiffness also has an impact. A softer sidewall and lower pressure can increase the contact patch, but can also impact handling negatively.

 

ant_8u,

Feel free to use the picture.

Steve,

Now you have it. It's also the reason we use driving techniques to control traction with weight tranfer.

Trail braking - Load the front tires, unload the rear tires for better rotation and entry into a turn
Lift throttle - Again to tranfer weight onto the front tires and off the rear tires for better rotation typically for mid corner corrections

etc. etc.

FYI we are grossly understating the complexity and real world application of this theory. The more you learn the more you begin to understand how little you know.

Bottom line is with in reason the tire compound will have a bigger impact on traction than the tire size. A 315 is not going to give you noticably more straight line traction than a 295 in the same compound. Wider is typically better (it doesn't hurt straight line traction, but helps cornering traction). This is all within reason of course as taller tire will affect gearing, bigger tires can be heavier and wider front tires can increase steering weight and frontal area.

BTW I don't have a 911 turbo yet, but I do run 19x11.5" rear wheels with 315/25R19's on the rear of my Supra (19x10" with 275/30R19's on the front).

Later, Steve

 

^ Indeed

My mind was blown the first time I started exploring this subject

I realised there is so much I don't (and will never fully) know

 

This is interesting...this is why drag racers use very soft tires with soft sidewalls and much lower air pressures...in fact on a good drag racing launch the drag tires actually wrinkle their sidewalls as the contact patch is optimized to deliver torque to the rear wheels and get a good bite on the launch.

 

You will also notice the tires grow significantly to make a tall tire with a long contact patch. This is exactly what's needed for straight line traction.

 

very true almost like they shrink in width and become very very tall just for a fraction of a second at launch...this can be seen very well during a drag racers burnout...

good info on this thread!