[Ronbo]

It will vary depending on the tire. Best thing to do is get one of those infared temp guns and take readings of the tread after driving for about a mile or so (no turns, straight line). You want a consistant temp reading across the tread. Too low and the center will be cool, too high and the center temp will be higher.

The temp reading can also reveal alignment problems when one half of the tire is hotter. Too much toe-in will cause the outside of the tire to heat up for example.