Answer:
There's a great misconception about tires that says tread equals traction. While it's true on wet roads and dirt, it is not true on dry, clean pavement. Rubber gives traction, not tread. The function of tread is to cut through water, dirt, etc by channeling it into the spaces between the tread blocks to allow the rubber to meet the driving surface. This is not needed on a clean, dry race track, and tread merely reduces the amount of rubber that meets the surface and thereby reduces the contact patch. Racing slicks have no tread and therefore give far greater traction by increasing the area of the tire's contact patch on clean pavement. However, in the wet they become virtually useless because the tire can no longer make contact with the racing surface; hence "rain tires" and off-road racing tires have tread.