Delring pinions are good for low power stock motors, but if you are planning to use powerful high speed or high torque motors, where the pinions suffer a lot (more over if u wear a low ratio 54/18 for example) these pinions get broken in a blink.
This mod comes with most common pinion sizes and each pinion comes with its screw, so you can use one pinion on each of your cars or just keep it till the moment your set up needs it. If you want top speed for running in easy zones, 18T will make you feel a new motor has been equiped, while if you want more power to climb dunes or play in a dirty place 12T or 14T is your choice. 16T will do good in any case
just a con, the colour teds to disapear when the pinion is used a lot. Pitch is 48.