Anyone experiment with "overdrive"?
 

For those who don't already know, overdrive refers to having slightly different gear ratios in the front and rear of the vehicle to intentionally drive the wheels at different speeds. For example, running 43/13 in the rear and 41/13 in the front. This will cause the front wheels to turn faster, and in theory the vehicle should have the tendency to "pull" itself forward rather than "push"

Does anyone have any actual experience with this? I know Xray offers overdrive gearing as an option, I'm sure some other manufacturers do to.

I'm just a bit curious about it, to see how noticeable the effects are and how much they affect the vehicle handling. Overdriving front vs. overdriving rear (seems like front would make more sense, at least to me). I have a variety of gear sets for my Jammin and thought about experimenting a little bit next time I pop the diffs out for a rebuild.

Sounds like overdriving the front would benefit on-power handling. Other than that, the CD would take up the slack between the F/R diffs.

Overdriving the rear just sounds like fun. :lol: Although it might help the drifters.

Actually I used to run overdrive in my xxx4g+ on the front. It worked really well to get tons of on power steering which the car always had issues with. Took a little setup to keep the rear in line but it did work well for me. Only bummer was it killed the skinny front tires way quick. Not sure how it would work on a 1/8 scale but it's worth a try if your looking for 180 inducing on power steering.

Works on rock crawlers :)

Experimenting.
 

It actually sounds like a nice experiment, but it really doesn't make a lot of sense to me. Imagine a cheeta having stronger front legs than back? I believe that it would seriously effect the way it chases down prey in a negative way. It seems to me that it would not be very efficient in comparison to having all four corners pulling nearly the same weight under the same power. If you have your diffs setup for better handling, which is setup to match the actual drivers preference that should be enough. BUT like I said it sounds like an interesting experiment to try. So give it a shot and share your results with us.

no reason to on a 1/8 and here is why

as long as you have a center diff you are always overdriveing the front due to the nature of how power transfer works (the exception to this is a center tortion and overdriveing will destroy a torsion very quickly).

a good example of ths is set your buggy up with the standard 5/7/3k diffs and go out an punch the throtle hard, it will ballon the fronts as it takes off but not the rears, that is overdrive, changeing the diff ratio in the rear would reduce this but the buggy would be much harder to drive and it will put alot of stress on the driveline.

on a xxx4 and a rock crawler it works because you have a solid center diff

if you want tighter turning then overdriveing the front is the worst way to do it, you would be better off tuneing the buggy to oversteer or moveing more weight foward

if you really want to drift. toss a oneway in the front and a spool in the back, that alot of fun

It should also be noted that overdriving in any way (cd or solid center) will wear the gears faster. It is just easier on the driveline if everything rolls together.

The only application where I would consider overgearing would be in mud, where the loss of traction saves the gears, or in rock crawling where the slow speed saves the gears.

(or racing an xxx4 where winning is more important than money)

Mugen offers this also on the mbx6.

They use it in very low traction condition. You can push the harder and it's easier to drive. You have to go up in oils to. 10-10-5 is the lowest they run with overdrive and 15-15-10 is more common. Overdrive causes the car to pull through because the font spins a little bit faster than the rear so it's pulling the car. It is not recommend to run overdrive on mid to high traction tracks, only on low grip/loamy tracks. Because the front spins faster than the rear, the diff is constantly working and the diff oil wears out faster in the middle. You have to renew the centerdiff oil faster to keep it consistent. However it lasts a raceday :) (let it sit for max 2 racedays)

I can see what you are saying, it does make sense. However, the center diff is not always unloading to the front, mostly just during that initial heavy acceleration and weight shifting. Seems like there would still be plenty of time where the center diff is distributing power pretty evenly, and the overdrive would be able to exert it's effect.

I can see both sides of it now, but it would be surprising to me if the big names like Xray and Mugen offered overdrive without it having any merit.

the first I heard of overdriving was the yokomo guys. they did it for on road with changing pullies on the belt drive. it wasthe big name guys doing it. I saw xray follow suit many years later, but then the yokomo guy is now xray canada president so...

it is a cool tuning tool. you have to try it out. really makes the buggy more responsive to input.

I'd say adding overdrive to the rear would give you more on power steering if anything. More off power steering too. When power is applied, the rear wheels spin faster than the front wheels causing the tendancy for the car to swap ends. In fact, the rear wheels will always break traction first (both in acceleration and braking) because they change direction at a faster rate. Because the front end maintains traction for a longer time, you get more steering.

They call it overdrive, but it's actually underdrive. Driving with a car where the rear spins faster than the front it not recommended. They will be very hard to drive and will naturally spin out.
When the rear is spinning a bit slower than the front, the pulls through turns. The rear follows the front and you can drive the car very hard on power.

It could see myself using it for very tight grippy tracks. I find changing the center diff to the spool very helpful in those conditions.