[JimboJames1972]

Hi Davo,

To know the right sized pinion you need to know other things - model of motor, track size and complexity, spur gear size and tire size.

Because GT12 cars run foam tires (which anve the anoying habbit of wearing down and change diameter) we don't bother with overall gear ratio, but we calculate the "millimetres per rev". In other words, how far the car will travel for one complete turn of the motor. This figure takes into account pinion size, spur size and tire size.

mm per rev = (3.142 x tire diameter x pinion teeth) / spur teeth.

The mm/rev you need will then depend on your motor make and model and the size of the track you are racing on. For example, a revvy motor on a tight and twisty little track might work best with a 55mm/rev setting. On the other hand, a motor with more torque on a big, fast and flowing track might work better with 75mm/rev.

What motor and track size do you race on?

If you ask other racers at your regular track what mm/rev they use you can find a suitable pinion by:-

Pinion needed = (mm/rev x spur) / (3.142 x tire diameter)

Hope this helps

James

PS if you have either an iPhone or Andriod handset there are several apps that will do all these calculations for you

PPS. If you are doing the above calculations "by hand" it does not matter if you are using 32 or 48dp pinions and spurs. However, make sure you measure your tire diameter in "mm" and not inches, cm or furlongs...