50t is the largest spur we make for the Slipperential - can work fine on the Caster truggy with a 1700Kv motor (12t pinion with 50t spur on 5s with a 1700Kv motor and truggy tires calculates to right about 40mph). Caster also makes a 10/46 ring/pinion setyup for their truggy and buggy I think.