[BrianG]

We run 51T spurs because that is the Ofna spur that fits on the strobe slipper and they are Mod 1, which is a little beefier than 32p/0.8m. Some use 40T because it is also Mod 1 and a good gear size for the Revo/Jato.

As far as motor selection, the bigger the motor, the more torque but less Kv it will have for a given wind (turns). Small motors can't dissipate the high power levels needed for heavier trucks. So, if you have a heavy truck, you'd want to go with a large motor for the torque and simply increase the voltage to get the speed you want. A larger motor will also handle taller gearing because of the added torque. You could go with a very low turn large motor to get the high kv, but then the current requirements would be a little ridiculous. It's generally better to get a high turn (lower kv) and use higher voltages for greater efficiency.

Think of it like a 4-cyl, 6-cyl, and 8-cyl in 1:1 cars. A 4-cyl works well in a light vehicle while maintaining light weight and fairly high gas mileage (efficiency). You could put a v6 or v8, and it would go faster, but you are barely using the power and efficiency would suffer due to the inherent losses in friction. Similarly, you don't want to put a 4-cyl in a big truck. You'd have to gear it so it would rev high and still go fairly slow because of the missing torque. And you'd still be stressing it so efficiency would be less than a v8 properly loaded.