SC10 Differential Options and Motor Gearing

SC10 Differential Options

SC10 gear diff

There are two options when choosing a differential for your SC10…

1. You can keep the Associated SC10 Gear Differential that comes with your SC10 kit or RTR.

2. OR, buy the Associated SC10 Ball Differential.
Gear Differential

We think the first option (gear diff) is best for most SC10 owners. The gear diff comes with your kit or RTR and it has proven to be an adequate differential mechanism for any level of racing. Another benefit of the gear diff is that it is very low maintenance.

If you decide to keep the gear diff, you need to properly fill it with grease. The SC10 manual suggests that you only need a drop or two on each gear, but don’t make that mistake. Your gear diff will run well for a few sessions, but then it will dry up. You need to fill your entire differential with the black grease provided in your kit. If you have an RTR, it would be wise to check your differential at some point and add grease if necessary.

You can also fill your gear differential with differential fluid (oil). Some people think the grease is better and others say that the fluid gives the differential a smoother feel coming out of the corners. Stick with the grease if you are still a beginner, but if you are ready to try something new, give the diff fluid a shot. We suggest starting with fluid in the range of 5000wt – 7000wt, depending on your track conditions. The beauty of using diff fluid is that you can adjust the weight to your driving style or track surface.

Ball Differential

Your other option is the Associated SC10 Ball Differential. The main advantage of the ball diff is how easy it is to tune. You don’t need to open up your transmission or even take your wheels off.

There is a big disadvantage to the ball diff. You will need to rebuild it every so often to keep it functioning properly. The rebuild kit costs about $15-$20 and you will have to rebuild this differential after every couple months to keep it in decent condition.

Here is a quick summary of the ball diff vs gear diff question written by Ray lan on the Forums:

“You should first try to understand why a car requires a differential in the first place. If you really understand, the rest of this post will be nothing more than a confirmation shot.

A gear diff is more durable and is maintenance free until the gears wear out, by then the car itself should have worn out. You can run them dry(no grease) or with grease of different viscosity. Tamiya Anti Wear is a very thick type of grease as compared to Tamiya Ceramic grease. The type of grease used affects the amount of tightness. Thicker oil/grease = Tighter diff action.
Gear diff have less consistant performance due to grease heating up during long runs causing the grease to loose viscosity, or by grease leaking out of the diff housing after prolonged use. Greased diffs require top up to maintain performance.

A ball diff requires more maintenance, replacement of diff balls and diff rings. The main advantage of a ball diff is ease of adjustability of tightness. A car’s differentials affect its driving characteristics a great deal. A driver who is able to setup his differential well will have the advantage of a better handling car. Some say ball diffs may be allowed to slip by not tightening the assembly too much, allowing the slippage to control torque going to the rear wheels. Contrary to popular belief a slipping diff will quickly overheat and damage the diff. If your car can’t handle without allowing the rear diff to slip, you need to look elsewhere, diffs must not slip.”

– Ray Lan from

SC10 Motor Gearing

SC10 Motor Gearing

Motor gearing is one of most important tuning options that you can play with on the SC10. Changing the gearing of your SC10 affects many things, including: Top speed, acceleration, motor temperature (motor life), and run time. Gearing will be different for everybody depending on type of motor, track conditions, and driving style.

The easiest way to adjust motor gearing is to change the pinion gear. The pinion gear is small gear that fits on the shaft of your motor. The pinion meshes with the spur gear. By changing the pinion gear, you should be able to achieve the gearing you want under most circumstances.

Most of the SC10 RTR kits come with a 87 tooth spur gear and a 20 tooth pinion gear. We suggest sticking with the 87t spur and experimenting with the pinion gear. Your first concern when looking for the right pinion gear is motor temp. If your motor is running too hot to the point where you have to stop every 5 minutes and wait for the motor to cool down, you may want to gear down from that pinion. There are some other things you can do to control motor temp but gearing down is the best way to control temps (see Checking and Regulating Motor Temp). Remember, if you can’t touch and hold the end of your motor can for 3 secs, then your motor is probably too hot. By following this rule you will be sure that you are not damaging your motor.

The second thing you need to adjust gearing for is the track you are running on. Does your local track have a long straight away? Does you track have a lot of stop and go action? Are there jumps that you need to hit but don’t have much room to get speed going? These are all questions of torque vs. top speed. The most important things to gear for in terms of the track are:

1. Are you getting the most out of your SC10 on the straightaways? Straightaways are the best places to pass your competitors and you don’t want to be losing ground here. I would say to error on the side of less top speed for beginners but as you gain more experience, you will need those extra RPM’s.

2. Do you have enough torque to get out of the corners and prepare for crucial jumps? I know on my local track there are two jumps that you NEED to hit. If my gearing is too high, it makes it difficult to get up to speed and I can’t hit those jumps. When I gear down, it is much easier to get up and hit the jumps, saving me some time on every lap.

The main issue here is gearing your SC10 to a point where it can do everything you need to do on the track, without threatening dangerous motor temperatures. Everyone drives a little different. Some like more top speed with more sliding around corners. Others prefer more torque with solid traction through turns. First you need to decide how want to drive, then look at what the track demands. After you have a pinion gear that feels right, check your motor temps to make sure you aren’t doing any damage.


Start with the 87t spur/20t pinion if you are running the RTR motor set up. Gear the pinion up if you are experience cool motor temps or not enough top speed. Gear the pinion down if you are having hot motor temps or not enough torque. You should have an array of pinion gears in your tool box so quick changes based on track conditions can be made.

If you are running a modified set up, like the Castle Creations 5700kV motor, then you will want a smaller pinion gear for most track setups. We suggest starting with a 87t spur and 17t pinion gear and go from there. From our experience, this motor runs fairly hot but the 18t is necessary to get the top speed we need during races.

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