http://travel.nytimes.com/2007/02/02/travel/escapes/02adventurer.html?8dpc
Outtake from article:
The most serious competitors make their own tires, drilling hundreds of holes in the tread, inserting screws, and padding the interior face with duct tape, rubber, silicon caulking and other secret concoctions. Screw size and type varies from racer to racer.
“My tire methods are strictly off the record,” said Mr. Henderson, who incorporates more than 600 screws to create a pair of medieval-looking ice-chewers that can corner at nearly 90 degrees on the glare ice of a hockey rink.