These spur gears are an excellent purchase for the TT01. By having two different tooth counts it is possible to experiment with different gear ratios. For rally purposes I prefer the 58 tooth(larger) spur gear, and for high speed tarmac runs I prefer the smaller 56 tooth spur. I would strongly recommend purchasing after market pinions opposed to keeping the stock Tamiya pinions when used with these spurs. All in all this is a very good purchase for any TT01 owner.