Track-Tac SST5 Purple Tire Softener - 12 Quart Case - Dirt & Asphalt RacingSourcing the right chemical prep from a trusted kart parts online retailer is the difference between hooking up on the exit or spinning your wheels. The Track Tac SST5 Purple Tire Softener is engineered for racers who demand precise, methodical control over their tire durometer. Unlike aggressive treatments that destroy the tire's internal matrix, SST5 gently tempers hardness by 0 to 5 points on cold tires, scaling predictably with each applied coat.