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Snaab9-2 wrote:Oh yes, I guess that would make sense. Very close to 80 mm....maybe slightly larger if they balloon out when spinning. One set are road tires and the other are low profile spikes. Both virtually identical in size.

Okay, with a 63-tooth spur gear and 80mm tire diameter, I come up with either a 19 or 20-tooth pinion as being close to optimal. Try the 19T if you're looking for quicker acceleration, and 20T if you're looking for a bit more top speed. If you use the 22T, check your motor temps to make sure it doesn't get too hot. What my spreadsheet does is help you find a spur & pinion ratio that results in a rollout of between 0.90 and 1.1 inch for 1 revolution of the motor. Once you know which pinions get you closest to 1.0", you can select the smaller one if you want more acceleration and the bigger one if you want more speed. Going too much in either direction puts you out of your particular drivetrain's sweet spot.

Thank you for doing that for me, pretty interesting. I will have to tinker with it (once I get a LIPO and stop using a 25 year old NICD that last 3 minutes ).

I am not sure how many turns the current engine in there has (I cannot find it using google). My question is, wouldn't the ideal pinion depend on the engine? If I had a 23 turn brushed vs a 9 turn brushless, wouldn't they want very different gearing?

Is this what gearing is the most efficient?

The way I understand the physics, the one thing that stays constant--no matter what motor you use in a 1:10-scale car--is the motor cylinder diameter. All 540-sized motors, regardless of brushless or brushed or kV rating or number of turns, spin the same distance in one revolution...so changing motors doesn't play a part in the calculation of a particular car's optimal gearing with respect to rollout; or the distance a car travels with one revolution of the motor. What matters a lot more is how tall your tires are, your transmission ratio, and spur/pinion ratio.

EDIT: I should mention that I did a lot of test calculations with other cars (not just Kyosho); I would be interested for any racers who have their cars dialed in (any make/model) to tell me what pinion they chose as the best one, and I could input the rest of the known variables (spur size, tire diameter & transmission ratio) and see how close this spreadsheet calculation is, to what works best for them. If anybody wants to share their winning combos, feel free to PM me (I realize the racers would want to keep that info secret, haha!).