One of the most commonly asked questions is "how should I gear my rustler?". There is no right answer other than "don't overgear". Here is the equation used to determine the final gear ratio of a TRAXXAS RUSTLER. Other rc's should not use this equation, because the transmission is different.
First, the big gear connected to the tranny is the spur gear. The lower the number of teeth on the tranny, the faster the top speed of the rustie will be.
Second, the small gear connected to the motor is the pinion. The larger the pinion, the higher the top speed will be. the smaller the pinion, the more acceleration and torque you will get.
here's the equation:
(#spur/#pinion)x2.72=final gear ratio.
What is final gear ratio? FGR is how many times the motor must spin to make the wheels spin once. here is an example of one of my gear ratios: 78 tooth spur divided by 23 tooth pinion = 3.4. 3.4 x 2.72=9.248. that is how I geared my rustler to race on road against the ol' lady's 4 tec.
*NOTE: that IS over geared! I only set it up like that to achieve top speed for one run!!! if you gear your rustler like that off road you might fry the motor, esc, battery, or any combination!
Well of course I race off road, so here is how I gear to race at the track:
#84 tooth spur #19 tooth spur. 84/19=4.42x2.72= 12. the track I race on has a long straightaway and lots of turns and a couple of jumps, so I gear in the middle. (the lowest gearing is the highest number, its kinda confusing. 15 is about the lowest for a rustler, 9 is about the highest gearing)
basically, the higher the final number, the more off road the truck will be set for, i.e. more torque and acceleration. The lower the final number, the better the truck will be geared for pavement with no hills, i.e. more top speed. the way I recommend finding out what is good for you is staring off with a small pinion and a large spur, and keep making it faster (larger pinion, smaller spur) until you reach a point where the motor gets too hot, then ease back on the gearing until it runs in a comfortable temp. zone.