got this off rc51.org.quick to the point article.
First off though we need to lay out the definitions:
DOT Street tire: a tire approved by the Department of Transportation for use on public roads
DOT Race tire: a tire approved by the Department of Transportation for use on public roads, but widely regarded as a purpose built tire designed to sacrifice longevity & wet weather grip for better adhesion under dry conditions only.
Race Tire: any tire that does not carry a DOT approval rating regardless of whether it has rain grooves or not (slicks) that is intended for use on competition road courses.
Contrary to popular myth the main difference between DOT street tires & DOT race tires is not the rubber compound. It is the construction of the belting plies in the tire carcass.
The belting in street tires is designed to give more stability & better ride when the bike is upright whereas the belting in race tires is designed for better grip & stability at high lean angles.
We have all heard the stories about Ricky Racer crashing his bike cause he was running race tires on the street & couldn't keep them warm enough etc & while there is some validity to those stories because the rubber compounds are designed to work in certain heat ranges, the overall statement is false & usually nothing more than an excuse for rider error. Cold race tires still stick better than a cold street tire .Race rubber being a softer compound than street rubber will be inherently more grippy than a harder street compound. Now if you have just recently abused your race tire or have installed a race take off then you may have either not enough catalyst left in the tire to provide adequate grip or you may need to put in a little time to scrub off the dead layer of rubber to get to some fresh rubber with good catalyst in it.
"What the hell is catalyst you say?" Well what really gives a tire its grip is a chemical catalyst in the compound that when heated makes the tire adhere better to the road surface. The reason racers sell race take-off tires even though they have more than half the tread left is because they have burned the catalyst out of the tires through either too many heat cycles or simply too much heat was generated in the tire period & now the tire no longer functions to their satisfaction or required level of grip. The hardness of the tire compound is only one part in the factor on grip as is the temperature range they are designed to run in. Tires pushed beyond their temperature range for extended periods will start to delaminate (seperation of the rubber from the carcass). Now I don't know about who you hang out with, but I know only maybe a handful of guys that can actually overheat a tire during street use... Street riders as a general rule simply do not have to worry about getting any tire race or street into the proper operating temp range as a normal sport riding pace will bring the tire into a useable temp range. Racers on the other hand have to be concerned with selecting the proper temp range due to the fact that delamination can occur if the tire is subjected to sustained temps above it's operating range.
Another misconception is the idea that race tires are no good in the rain because of their lack of grooves in the tread. While it certainly is true that a tire needs grooves to channel water away to prevent hydroplaning, the real reason for lack of wet grip is again the compound. Street tires generally contain lots of silica in them to provide better heat dispersion (aids in consistent tire operating temps) & wet weather grip.