RC Car - How pinion gears work

The RC Car and Radio Control Racing Web Site

How Do I Choose the Right Pinion Gear?

Please see the article on "How Gear Ratios Work" for an explanation on how exactly one finds a gear ratio. This article will focus mainly on how to choose that perfect gear ratio.

First of all the answer to this question depends on whether you are running a stock motor or a modified motor. As a general rule of thumb, you will run a larger pinion gear with a stock motor most of the time. In order to simplify things, stick with the spur gear that came with your vehicle and change the pinion gear only. Only once you have gained sufficient experience "gearing" your vehicle, will you be ready to try different spur gear sizes.

I remember back several years ago when battery and motor technology were not as advanced as today. You would choose your pinion gear simply by choosing the largest pinion gear you could use without fully draining your battery ("dumping") before the end of the race. A little more recently, you could tell when you were over-geared (using too large a pinion) by checking to see if your motor was excessively hot at the end of the race. You knew that you had to go down a few teeth if you burned the motor’s brushes after one 4-minute run! With today’s battery technology, the possibility of dumping before the end of a 4 or 5 minute race is very unlikely. Motors are also designed to run much more efficiently and with less heat build up. The advantage today is that you can choose your pinion gear solely for the purpose of tuning the handling of your vehicle to suit the track conditions.

Choosing that perfect gear ratio depends on many factors. The condition and layout of the track are very important. If the track has a long straight section and wide sweeping turns, you might want to run a slightly larger pinion. If there is no straightway and it’s all tight infield, perhaps you should run a smaller pinion gear. For off road, the number and size of the jumps will also affect your choice. If you need a little bit more torque to quickly accelerate over a set of triple jumps, then run a smaller pinion. Also if track conditions deteriorate, i.e. becomes bumpy and or slippery, a larger pinion gear might help to smooth out the vehicle’s acceleration.

The gear you choose will also depend on the motor you are running. (Please see the article "Which Motor should I Use" for more information on different motor winds). Generally if you are running a lower turn modified motor, you will run a smaller pinion because these motors have higher rpm and less torque. The opposite is true for higher wind motors, these have more torque but less rpm, therefore a larger pinion is required.

It’s generally a good idea that when you are experimenting with different pinion gear sizes, to only change the tooth number by one tooth at a time. This way you won’t "overshoot" the perfect size. Also, start off with the manufacturer’s recommended pinion size. Some companies, such as Team Losi, offer a chart in the assembly manual showing the suggested pinion size for different modified motor winds.

As you might have guessed, the only way to find the proper size pinion is to try each gear change out on the track. Try to drive your vehicle exactly as you would during the race, as many people drive differently in practice then they do in a race situation. Driving under race type conditions will help get you very close to the right gearing. Once you have actually run a 4, 5 or 8 minute race, you might decide to change one gear up or one down. Now, you should be right on the money!

Let's take off a few tenths per lap,

"PRO"