My next generic question about z car setup, this one in regard to tire stretching

[BTF/PTM]

Hi everyone,

I've another question that isn't specific to z-car science, but is relevant to the general setup thereof.

My question is in regard to stretching a tire across a wheel for which it's too narrow. A 205 tire on an 8 inch-wide wheel, for example. It seems that, in many cases, this is done simply becuz the owner likes the look. In other cases, it seems it's done because the proper-width tire doesn't fit under the fender. My question is, what does this do to a tire in terms of its structural integrity and performance? Is there a threshold where a tire can still perform safely under aggressive driving conditions (autocross or a track day, for example)? At what point does the trade between making it fit and pushing the mechanically safe limits of the tire become dangerous?

And, to specify a bit, I'm referring specifically to road-legal tires. I understand that specialty race tires are often built with different types of sidewall (cantilever type comes to mind).

Thanks, everyone!

[John Coffey]

There are generally no structural integrity issues with the tire when stretched. The big issue is popping a bead under lateral load or from pot holes. The tire pressures you'll have to run to prevent bead popping will significantly reduce grip. To get the best performance out of a performance tire it should be mounted on a rim that is equal to to or 1/2" wider then the actual tread width measured from tip to tip of the wear triangles.