Description:

Hardened steel to increased wear resistance and improve fatigue life
Nitrided to enhanced hardness corrosion resistance
Tooth count: 13T 14T 15T 16T 17T
Tooth pitch: 48 pitch
length: 9mm
For shaft: 3.175mm

Package include:
1 X 48p 13T pinion gear
1 X 48p 14T pinion gear
1 X 48p 15T pinion gear
1 X 48p 16T pinion gear
1 X 48p 17T pinion gear
5 X Screws
1 X Hex Key

Make sure you thread lock the grub screw. They are hard to find when they fall out.
Larger gears will result in higher speeds while smaller gears provide more torque.
For quicker acceleration go for a smaller pinion gear (with fewer teeth) and larger spur gear (with more teeth).
Your car will accelerate off the mark very quickly with more torque, and you'll also benefit from cooler running temperatures, extending the life of your motor and ESC.

How to install the pinion gear:
You will probably need to loosen the motor a bit, in order to fit the pinion gear on. Make sure you lock it in place on the flat portion of the motor shaft.
When you are tightening it back up, make sure you leave about a gap between the pinion gear and the spur gear. That gap will be very small. It should be about the thickness of a piece of paper.