Changes how the car grips the track, and therefore how it accelerates, turns, and stops. Generally racing tires (hard or soft) will deteriorate faster but grip better, resulting in better performance of the car. Additionally, the layers of the tires are bound together stronger, street tires can actually start to separate if you push 'em too hard. So performance and safty are influenced by tire construction.. I know that's very general, but if you try to go into even a slight amount of detail it gets messy.
Since when did the world start accepting the spelling of Tire with a "Y"?
euro and aussies I think spell it that way...
Actually it's fairly simple. The softer the tire, the better it grips. There is a downside though. It generates greater heat, has more rolling resistance than a harder compound and wears out much faster. The harder the tire, the less it grips;the upside though is less heat, longer wear and less rolling resistance.
I agree with all the responses from all the posters. The answer to your question is: R-compound tires once warmed up to the right temp. on the track will generation more traction than street compound tires. Even more important, R-compound tires do not over heat and turn greasy (loss of traction) like street tires. When I use my street tires on the road course, I have to let them cool down after every 2 hot laps (or after excessive scrubbing getting into turns too fast), while with the R-compound, the problem is the other way - don't let them cool down too much or they will lose traction! R-compound tires last only 30% as long as street tires though.