Does size matter ?.

[lincpimp]

A smaller spur, or larger pinion will increase top speed. A smallre pinion or larger spur will decrease top speed and increase torque via gear multiplication.

On a side note, I always think it is best to use the smallest spur and largest pinion to achieve the correct ratio. That way you will see less pinion wear, and the gear mesh is greater at any point due to better engagement of the teeth. Anyone who has run a very small pinion with a large spur can attest to the fact that is does not feel as smooth as a larger pinion with a smaller spur.

This mainly applies when you have different diff and tranny ratios to choose from. I noticed it quite a bit when I put my slayer together. Because I am using a revo tranny, which has more reduction than the slayer tranny, I had to run a much larger pinion. I currently have a 20t pinion with a 36t spur, and it runs very smooth and can be set up with very little backlash in the gears.