I don’t have a lot of experience or parts for NSR. My Corvette came with the 25K motor. I tried it for the first time today with a 33-tooth spur; it was undrivable. Even with weight it was very twitchy, especially under braking at the ends of the long straights. I ordered 34- and 35-tooth gears today. I still plan on running with the 25K motor, hoping that the higher numerical gearing will be enough to calm it down. I am ordering a 36-tooth gear as well.
Russell