How to setup RC diffs - Setup Guide Articles

How to setup RC diffs – Setup Guide

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RC diff oil tuning is very important. Here’s a “How to setup RC diffs” guide to help you to understand how to get the best from your diffs.

How diffs work:

Differentials are part of all buggies, truggies and monster trucks and their designs vary slightly from one vehicle to another. However their action and setup still the same. The center diff is the most important because it transfers power to the front and rear diffs. The front and rear diffs receive the power from the center diff and distribute the power to the left and right wheels.

Diffs are also very important when the vehicle is turning. When turning, the outer wheels spin faster than the inner wheels. Without the front and rear diffs, both wheels will be spinning at the same speed making cornering harder and increasing dramatically turning radius.

How to setup RC diffs - Setup Guide Articles  Most of the diffs are composed of four spider gears and two cross pins

Understanding what is happening:

Basically, diff transfers power to one of its outdrive. By design, the easiest outdrive to spin (with less resitance or traction) will receive the power. This also means that the wheel or the end of the vehicle with less traction will receive most of the power. This is where diff fluids are important. You can compare diff action to a lightning. The lightning finds the shortest route to hit the ground. In our case, the power generated by the engine will find (through the diffs) the shortest (and easiest) route to spin the wheels.

Differentials can be filled with different weight of silicon fluid. Depending of the manufacturer, the weight (viscosity of the fluid) varies from 1000wt to 100 000wt. The greater is the number, the thicker the fluid is. Some RTR vehicles come with grease filled diffs. Grease is equivalent to 1000wt diff fluid. The diff fluid “locks” or “retards” the diff action. A diff filled with 1000wt fluid will spin more freely and will transfer power to the “looser” outdrive faster than a diff filled with 50 000wt diff fluid. This will make the “looser” wheel or end spin and loosing traction while the opposite outdrive receive no power.

Some manufacturers have released different types of differential. At the opposite of the conventional diff, the Torsen diff transfers power to the wheel that has more traction. Losi recently released the SmartDiff, a system that “locks” the diff when accelerating and “frees” the diff when off power or braking. Xray also offers a similar diff called Active Diff.

Important note: Because diff action is all about traction, make sure you have the right tires for your track surface before experimenting with your diffs.

The center diff:

When accelerating, weight is transferred to the rear end of the vehicle. The rear wheels get more weight and by consequence more traction than the front wheels. The center diff will transfer the most of its power to the front wheels because they are easier to spin and will make the front tires ballooning. This reaction is also call, diff unloading. To avoid this situation, thicker center diff fluid will be the way to go. But going with thicker fluid will not completely stop the diff from unloading during hard acceleration. The idea behind center diff adjustment is to find out which fluid thickness will give you the best acceleration all around the track without scarifying performances.

How to setup RC diffs - Setup Guide Articles
It is easy to recognize the center diff with its large spur gear

The fluid selection must be thin enough to transfer more power to the front than the rear when accelerating. Why? Because you need your front wheels to have more power to help your buggy to exit corners and to track straight under acceleration. The fluid must also be thin enough to not send too much power to the rear wheels which will make your buggy over steer when exiting corners because the rear end will spin and loose traction. A basic center diff fluid weight for buggies is 7000wt and for truggies 10 000wt.

Thicker fluid in the center diff will make your rear wheels push the buggy while thinner fluid will make the front wheels pull the buggy.

To get the best from your center diff, don’t nail the gas. Go progressively with the throttle, this will prevent traction lost.

The front diff:

Changing front diff fluid directly affects on and off power steering. Thinner fluid will increase initial cornering and off power cornering. On another hand, if you go with thicker front diff fluid you lost initial cornering and off power cornering but gain when exiting corners. This is due by the fact that the inner wheel turns slower than the outer wheel. Thinner diff fluid “frees” the diff action and makes it easier for the diff to turn its two outdrives at different speed.

See what happens when you nail the gas while the front wheels steer left or right. The inner wheel will get the most of the power and will balloon. Thicker diff fluid will “retard” the front inner wheel ballooning effect. A good basic weight is 5000wt for a buggy and 7000wt for a truggy.

The rear diff:

The rear diff is the easiest one to tune. It should be tuned to be “free” enough to not decrease cornering but it should also be tight enough to prevent the inner wheel from ballooning. At low speed or off power, a rear diff with too heavy fluid will decrease steering because it is harder for the diff to rotate the inner wheel at a different speed of the outer wheel. A too heavy fluid will also make the vehicle fishtail when exiting corner causing over steer.A good basic weight is 3000wt for buggies and truggies.

How to setup RC diffs - Setup Guide Articles
When turning. the inner wheels spin slower than the outer wheels. The weight is transfered to the outer wheels.

If you want more steering entering corners, use:

  • Thinner front diff fluid
  • Thinner rear diff fluid


If you want more steering exiting corners, use:

  • Thicker front diff fluid
  • Thicker rear diff fluid


If you want more forward traction, use:

  • Thicker center diff fluid


For better bumps handling, use:

  • Lighter front diff fluid
  • Lighter center diff fluid


Starting diffs setup for buggy:

  • Front: 5000wt
  • Center: 7000wt
  • Rear: 3000wt


Starting diffs setup for truggy:

  • Front: 7000wt
  • Center: 10 000wt
  • Rear: 3000wt


How much fluid to put into the diffs ?

If you overfill your diff, it will eventually leak. To make sure my diffs are filled properly, I first begin by filling the diff half way and then I rotate the diff gears to be sure fluid goes inside the gears. When fluid has made its way into the spider gears, I fill the diff until the fluid reaches about 1mm of the top.



There is no perfect setup. One setup will increase forward traction; another will increase off power steering while decreasing speed when exiting corners.

It may take you many tests before you find out the good setup that works fine for you. Take your time and tune only one diff at the time. Begin with the center diff, followed by the front and by the rear ones. The harder is to understand what diffs do and how they react to changes. Once you get familiar, diffs setup will have no secret for you.

Sylvain Lafrance

Sylvain Lafrance

Hello, my name is Sylvain Lafrance and I am the man behind I have bought my first hobby grade RC in the early 90s. With years, what that started as a simple hobby, quickly became a strong passion. I am so much passionate about R/C that I have created in 2006 to share my experiences with R/C products that I use for racing and bashing. Follow me !

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21 thoughts on “How to setup RC diffs – Setup Guide

  1. hi this article was most helpfull thankyou very much
    i tried 7000 F
    7000 C
    3000 R For my truggy on our track worked good and am going to try 10,000 in the center.
    my buggy is 5000 f
    5000 c
    2000 r

    1. Very helpful article, thank you! Could you add a section about how fluid is actually put into the diff? I assume that the diff housing should be completely filled up?

        1. Hi this article was very helpful. I have a hyper 7 nitro any suggestion which oil percentage to use in front , rear ,centre diff please.

  2. Hello, can you please specify the named oil viscosity values in cSt (centiStokes) ?
    I am not aware of any viscosity measurement unit called “wt” (“weight” I asusme).
    Some vendors use “wt” to disguise their actual cSt to force customers to buy their overpriced re-packaged stuff rather

  3. Is it recommended to have thicker fluid in the from than the rear. Or could it be setup up the other way round and what effect would that have?

  4. I have a Vorza and going to only use for speed run I am running xl2 esc with sss 4092 motor someone said to run 5000wt in center and 1000wt in front and rear diff. Will this be a good combo for straight speed runs ?? Attempting 100mph for the first time

  5. Any manufacturer on the market will use weight(wt).Rc doesn’t use CST as a measurement. And if they do they aren’t very mainstream.I would stick with rc specific silicon lubricants.Not something you want to cut corners or cheap out on.You will end up blowing out diffs or damaging O rings and gaskets.

  6. Hi
    Question.. for off road buggies – 1/5 scale
    1-Whats difference in handling if you use a center diff locker
    2- a lock front diff only and with center non lock diff

  7. Hi,
    I have an HSP 1/10 4WD buggy (BL) that I have started experimenting with the front diff fluid. All the guides that I have read are ‘centred’ around having a centre diff. In my case without one should I follow the same rules? I have fluid thing from 5k to 50k (7 bottles) thanks.

  8. Awesome article. I’m only not getting in to rc but am absolutely addicted! I’m based in the UK and have a talion 6s which is brilliant but I do want to get the best out of it. I do a mixture of driving, occasional speed runs on road, gravel, dust, grass and of course jumps. I’m keen to see how your recommended truggy startup varies to the standard talion setup which is 10k CST/100k CST/10k CST but I’m finding it almost impossible to get a WT to CST conversion. Please could you quote your recommended starting setups for both buggy and truggy in CST please?

  9. Thanks for this write-up. Question: how much does diff oil expand due to ambient temperature. It can get hot here in Phoenix, even after the sun is down. Should the diff be filled perhaps a bit less?

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