Can someone explain exactly what differential oil does and what effects the different weights have on an R/C car?

If you pick up your truck and spin one tire the other one should spin in the opposite direction. What the gear oil does is limit or enhance the ability of the tire to spin in the opposite direction at various rpm's and power inputs.
The thicker the oil the less the tire will spin in the opposite direction. Meanwhile the thinner the oil the more freely the gears spin.
The reason for using different oils depends on how or where you run. In a tight area with lots of corners you will want to use a lighter oil so the truck doesn't spin out from both of the tires applying power. On long straight aways and in a drag racing situation you want both of the tires to receive power so you will use a thicker oil.
Unless you race competitively you should probably just use grease in the diffs. That is what most of us use and it will work for the occasional race.

I hope this makes sense,



rolland

That makes all the sense in the world...thanks Rolland

Or to put it another way.
The main difference between the fluid weights is that the thicker diff fluid increases the ability of the gears to “lock up". Thus, helping to give you an equal amount of power to both tires. Even if one tire is spinning in the air and the other is on the ground, the tire on the ground will recieve more power with the thicker oil than if the diff had a thinner oil.

In saying that with thinner oil on a tight track would more suit a novice driver as power is transfered more to the tyre with the least grip (usually the inside tyre because of the outside tyre being "loaded up" with the weight transfer) this can harm acceleration but makes the car easier to control. (as Rolland said less chance of both wheels spinning and losing control) but for an experienced driver, a thicker oil will provide less inside wheel spin and more evenly distributed power, thus quicker acceleration, but more chance a spin out.

you guys ROCK!