Chapter 5: gearing
This is probably the most straightforward issue of all. In most cases, the best gear ratio is the one that allows your car to accelerate as fast as possible, without over-revving your motor on the straight. So finding the right gear ratio is quite simple in most cases: just make sure the motor reaches maximum revs towards the end of the longest straight.
However, in some cases it can be beneficial for your lap times to over- or undergear your car: a slightly undergeared car will accelerate faster, so the track is full of short straights where acceleration is very important, you might want to consider a smaller ratio. Overgearing is frequently used to prevent wheelspin under acceleration, mostly on low-traction tracks. It can make the car somewhat easier to drive. It's only advisable on tracks where wheelspin is a problem.
A gear ratio indicates the number of revolutions of the motor has to do for the wheel to complete one full revolution. For example: a ratio of 9.0 means that when the motor has done 9 complete rotations, the wheel will have done just one, if the motor has done 18, the wheel will have done 2,...
Here's the tricky part: a higher number means a smaller ratio, and conversely a smaller number means a higher ratio. So 9.0 is a taller or higher ratio than 10.0. Think about it: if the motor has to do less rotations for the wheel to do one (smaller number), the car will go faster for the same rpm, which means a taller ratio.
