overdrive front and rear?

[DTA510]

I bein doing alot of hill climb/rock crawling and keep end up in situations where I see my scx10 doing pushing with the rear then pulling with the front so I was wonder how well the overdrive in both axles would work,

[mikebecher]

Underdrive in the rear will give you better climbing ability. It allows the front to do more of the pulling which is where your weight should be.

[JohnRobHolmes]

Underdrive also lets the driveshaft spin faster, so for any given power and speed there is less torque twist. More geardown in the axles and increase the motor pinion to compensate.

[Big Bill]

What about Over Drive in the front Standard ratio in the rear, would it be the same as UD in the rear? I have used OD in the front for quite some time I like that they increase the front wheel speed it some times help with sharper turns. I would like to try the UD rear for a change. I am just thinking out load, but wouldnt the lower ratio in the rear increase torque twist? Thanks

[mikebecher]

OD in the front and standard rear would get you a similar wheelspeed difference as STD front / UD rear which improves both climbing and steering. But, OD gears have poorer mesh so are more prone to stripping and will exacerbate the torque twist because it's harder to turn the OD diff gear. The lower ratio combination (36/14 or 2.57) is actually the overdrive ratio. Underdrive is 43/13 (3.31) and standard is 38/13 (2.92).

You should see less torque twist if you go UD in the rear, and like John said, you can make up for the lost speed with a slightly larger pinion.

[DTA510]

Can I take the front diff out and put it in the rear?does any know the stock gear for from /rear?

[mikebecher]

Originally Posted by DTA510

Can I take the front diff out and put it in the rear?does any know the stock gear for from /rear?

There are 4 sets of diff gears:
stock (38/13) AX30392
HD overdrive (36/14) AX30401
HD standard (38/13) AX30395
HD underdrive (43/13) AX30402

IMO, the best combo is standard/underdrive followed by overdrive/standard (all HD of course).
Some people run overdrive/underdrive but that's a lot of stress on the drive train. Others run underdrive in both to minimize torque twist and because they have the best mesh.

[Dwill]

Yep, I'm running over drive front - under drive rear. Plus low hearing on the pinion. I still can't make much speed on flat ground or I'll drag the rear end around a bit. I'm pushing it with a Tekin ROC412 1800kv running on 3S. It's pretty torque, I'm thinking about going down again pinion size to pull a little more toque out of. My G6 climbs pretty well though, but like speed isn't what I was after. I've got the current limiter turned way down so that it doesn't accelerant very fast and I'm running pretty start power so it can move smoothly from a stop and at low speeds.

Still I'm thinking at the next maintenance tear down I might go back to the stock ratio in the rear, using HD gears of course.

[DTA510]

Would overdrive /overdrive be to much ?

[mikebecher]

If you're gonna run the same ratio front and rear you should make it underdrive. These gears have the best mesh and do more to combat torque twist. You can make up for lost wheel speed with a larger pinion.