What pinion and spur for Kyosho Lazer ZX7.5 with 13.5T motor?

For the Kyosho Lazer ZX7.5 with a 13.5T motor, start with a 25T pinion and the stock 78T spur. That gives a 7.8:1 final drive ratio. Confidence is high, and racers in this class typically run 23–27T pinions.

Check motor temperature after a short run. If it is too hot, drop one pinion tooth and check again.

For the Lazer ZX7.5, start with 200,000 cSt center diff fluid, the kit setup value. The available setup information does not give a separate recommendation for high-bite carpet or for a 13.5T motor.

Center diff fluid affects how freely power can transfer between the front and rear. Treat 200,000 cSt as a baseline rather than a carpet-specific proven setting, and change only after testing. If you share what the car is doing on throttle, such as pushing wide or feeling loose, I can suggest which direction to try next.