Originally Posted by patiofurniture

60k has been really good for most indoor clay tracks. A good balance of acceleration while having really good rear-end power delivery.

For a looser outdoor track you can go a bit thinner up to 40k lighter, you could maybe go even more just depends on the tires, dust, etc. on how much it unloads to the front. The center diff oil will also depend a little on the motor you are using to help get the best power delivery and grip.