Tire limitations

[Damn True]

Read an interesting statement in a really old thread that didn't get expanded upon enough for me to understand it.

The gist of it was that from a handling perspective, there is no sense swinging 315's around on the back of the car if all you can fit up front is a 245. Apparently the discrepancy in available traction causes more problems than it solves.

Could someone who has some understanding of this expand on it please.

[JLM]

From my understanding it's the same premise as the rear-end working better than the front end. More available traction in the rear than in the front so you tend to understeer.

Handling is about balance.

I'm not the expert, hopefully they'll chime in.

[Mean 69]

In the very general case of a typical front engine car, this is true. There are a lot of variables that can affect this, and some ways to improve upon it, but the bottom line is that a bigger tire will have more grip. Or rather, a "wider" tire will almost always have more lateral holding capability than a similar "narrower" tire.

On a front engine car in a hard turn, the outer front tire will be loaded the most. Typical PT type cars have about a 55% front weight distribution bias, more or less. As such, along with the weight transfer from cornering g-forces, that front tire is carrying the bulk of the responsibility of keeping the car from spinning. At some point, the forces will overwhelm the tire, and it will begin to slide, creating under-steer. A little under-steer is usually the most comfortable for a typical driver, because it is the easiest to catch if things get out of hand (let off of the gas, turn the wheel more, etc). But, if you have way more lateral grip on the back than on the front, understeer can be significant.

One way to take advantage of the relatively greater rear grip is to use the throttle in turns, by introducing a bit of forward acceleration, you can transfer some of the load to the rear tires, including cornering load.

Clearly there are things you can do to tune the suspension of the car to help mitigate understeer, but in very general terms, this is what you can expect with a dramatic tire stagger.

Mark