Roc8Ray - Dana (The Bat) can correct me if I'm wrong... Using multiple gears (derailleur or some type of transmission) can be an advantage on a twisty track where the car speed changes dramatically from one part of the track to another. Keeping the motor in its most efficient rpm range is the goal as long as the gear change is accomplished smoothly and without a huge change in gear ratio. A sudden big change in gear ratio equates to a big change in motor speed and could cause power spikes on the current draw.

RestoRod - It depends on the motor and its efficient rpm range. Motor manufacurers provide info at what rpm range their motors run most efficiently. The challenge then is to figure out what ratio is necessary to keep the motor in its efficient range on the track you are running. The Scott 1hp motor is most efficient at 2800 rpm. If we are running on a tight course like the parking lot course at USF Tampa, the average speed is about 22 mph. If I calculate the rpm's of the rear wheel, it needs to turn 370 rpm to go 22 mph. Now divide 370 wheel rpm into 2800 motor rpm and I come up with a target ratio of 7.56:1. Just to keep a little extra speed available for the long backstretch, I would probably go with something in the range of 7:1.

For sprockets I try to determine what may be the lowest and highest ratios I might need, get a big enough wheel sprocket to achieve it, and buy a selection of motor sprockets to give me a selection in between.

Steve - I saw that car in your other thread. It's amazing what electric power is capable of these days and I believe that industry has only scratched the surface of future potential. The down side right now is the expense of converting a vehicle to electric, but those costs are coming down as more stuff becomes available...