[PhYrE]

Look at the sidewall of the tire. Probably a 1/3rd of an inch from the tire tread is a triangle pointing to the tread of the tire (up/down or side/side depending on where it is). This is printed on the sidewall.

When tracking, this triangle points to where the scrub marks for the road should be. Thus if it's nowhere close to it, you can let out more air and use more sidewall. If it's over it, you should increase the air as it's riding on the sidewall.

Now you shouldn't do this on the street. You'd let out a lot of air to get to the mark, you'd have terrible fuel economy, and your sidewall would heat up like anything and eventually wear.

That said, it gives you a mark if you're ever looking for 'spirited' track driving. That's how you should get to the figures mentioned in post # 2 to maximize the grip on the track.

On the street go up a few pounds for better fuel economy. Go down a few pounds for better grip. Anything too far beyond that causes drastic wear.

Note of course that any difference in size will alter these figures.

-M