Gear-Diff for low-to-mid traction dirt
 

I know I know...I should be running the ball diff (which I have), but I'd like to give the gear-diff a shot as our club moves from indoor carpet to outdoor dirt. I understand that most on this forum are in the UK where tracks are different than our North American counter-parts (I'm in Western Canada), but I'm wondering if there are any with experience with the set-up for dirt/gear-diff?

I ran 1000cst in my diff for the whole of the 7 month indoor season (high-grip carpet), and I expect to initially try 2000cst outdoors but would love to hear ideas!

I will be doing the rear-shock mod, and may try RM4 as traction can be low at the start of the season (later on the track get "sealed" with some, I don't know, glue or something).

Thanks for your time thinking of this!

You have it backwards.

The lesser the traction of the surface you're running, the lighter the weight gear oil you should be using. Going heavier, as you're suggesting, will just make the diff lock up (and the car spin out) that much easier.

I see, I'll maybe rebuild it and put 1000 back in there for the outdoor season. I got the idea of 1K for indoors from a set-up sheet of Jorn Neumann's, seemed good, but I'm new to carpet.

If it was me I would run 2k for medium to high-ish tracks, 3k for high to very high-ish and 1k for low-ish traction tracks.

One thing that has always confused me though is why you should run a ball diff on low traction surfaces? You could run a gear diff with shock oil if if you wanted to to get loads of grip but with a ball diff you have to have it pretty tight to stop it slipping.

Hiya,

I've been running on slippery indoor surface (polished wood) so far with a gear diff. I went down to the 700 oil usually used for shocks. I've had no problems and may even run it at 600 if need be.

This loosened the diff up more for low grip fine. You cannot go too light though as you may start damaging the diff, I've heard, so maybe go down in stages if trying it out.

Hope this helps.

If you're running on a very low grip track then I'd say what you need is "drive" out of the corners .. and you won't get that with a loose diff. 5000cst oil has a similar feel to a good ball diff and might be a good place to start.

I use xray 700 gear diff oil in mine using mm4 layout on loose stuff i may go to 2000 if tyre wear isnt too bad

When I was looking into what oil to use I did see one where Jorn Neumann was using 500cst.

High Grip = lighter oil as will help it rotate

Low Grip = Heavier oil

HTH

This is what I thought as well. From what I know with a loose diff your car more easily gets wheelspin on one side and a lack of drive on the other. On low traction surfaces you easily lose grip on a wheel (in particular the inside wheel in corners), resulting in a lack of drive through/out of corners and depending on the track it may unexpectedly bite on a certain side. One of the things your car might (also) suffer from is a tendency to start fishtailing (in particular out of corners or on bumpy tracks) because the highest grip switches between left and right and back all the time.

Of course, too thick a diff will cause massive understeer on any surface. However,my rear motor buggy didn't show any more understeer with a 5k oil filled gear diff on high bite astro as compared to a ball diff, so you don't necessarily need to put shock oil in your diff like some setups suggest :p

Another plus to going thinker on the oil is the car is much more stable under heavy braking ... which would be a benefit to a RM car on low grip ...

If your running on high grip track and you have understeer you would need to run lighter oils.
Running really light oils will make it diff out and become very hard to drive.

In an ideal world you would run ball diff in wet/loose conditions and Gear'd diff in med/high grip

i realy wonder why people often says, that a thinner oils goes better on a loose track.
i found out that a to thin oil in a gear diff ( 1000-3000) let the car rotate too much if one wheel loose traction and thats what happen on a loose track

with a thicker oil in my gear diff ( actually 12000) the car feel more consistent and i can pull it more without rotating too fast.

if i tighten my ball diff, that it would not slipp, i would compare it with a gear diff with 10 k in it.

mihael