Starwheel carbon primary belt, 640-8M-25, for the Surron Ultra Bee. It runs between the motor pulley and the jackshaft, so it carries everything the motor makes before the chain sees any of it.
Primary belts stretch and lose teeth with heat and hard launches. Once the teeth start skipping you get a bang on takeoff, and the pulleys wear next, so a belt that has gone soft is worth changing before it takes hardware with it.
