Originally Posted by
razzor
filling the diff keeps the diff action consistant. if not full the oil gets airated and thins as well as heats up more.
Also different viscosity oils change the diff action/slip characteristics unlike a real cars diff that uses the oil for mainly lubrication.
generally the more traction there is you can go a bit thicker on the oil.
However on a low traction dusty tracks it can be a handfull and a ball diff feels better.
On low traction you'll probably be better off with the gear diff if you can get the handling balance you want with the setup. The gear diff will let you put more power down as long as you don't lift the inside tire. I have a feeling gear diffs will be an area of focus for the TC companies in the next year or so, as the ball diffs are less and less able to handle brushless motor torque.