Motor Gearing

Determining Gear Size

Number Of Teeth

I sometimes hear about someone who does not know how to determine the number of teeth on the pinion or the spur. One suggestion obviously, is to count the teeth. However, that's not necessarily a enjoyable experience, and with most pinions and spur gears is unnecessary.

Below is a picture of two pinion gears, a 17-tooth and a 21-tooth. You'll notice that both are plainly marked on the end with the number of teeth they have. You'll find this holds true with most pinions until you get below 14 teeth. At that point, most will not be marked due to their smaller size. However when you get to that small of a number of teeth, you can easily count them.

Next you'll find two pictures of some Traxxas spur gears. If you look closely you will notice the number of teeth on each of them as well. One is an 81-tooth, and one is an 84-tooth. Notice that for illustration purposes I've colored the numbers with a permanent marker to help them stand out. Without the marker they are a little harder to see, but they are there. The two photos show both sides of the spur gears and you'll notice that both sides are marked with the number of teeth they have. This is standard for Traxxas spur gears. Other manufacturers may put the number of teeth on only one side, but I have yet to see any spur gear that doesn't have some marking indicating the number of teeth it has somewhere on the gear.

Gear Pitch

Gear pitch is an item that many newcomers overlook when buying a gear, and buying the wrong gear pitch will only result in difficulties when running your truck. Even seasoned veterans may only have a vague understanding of what gear pitch really is. Gear pitch relates to the size of the teeth, and two gears with different pitches will not mesh properly.

Gear pitch is the number of teeth that would be on a gear, if it were 1 inch in diameter. So a 1 inch 48-pitch gear, could hold 48 teeth around it's perimeter. While a 1 inch 32-pitch gear would only have 32 teeth. This is because of the difference in size between the teeth. The lower the pitch, the larger the teeth on the gear. Larger teeth (smaller gear pitch) provide more strength per tooth than smaller teeth (higher gear pitch) do. You'll find that 32 and 48-pitch gears are common for off-road trucks because of this fact.

Below is a picture comparing a 32-pitch gear, on the left, with a 48-pitch gear, on the right. You can easily see the size difference between the teeth on the two gears.

Physical Limitations

When changing the spur gear in an Electric Stampede you should keep in mind that there are physical limitations to consider. If you plan on using the gear cover, the largest spur gear you can use is a 90-tooth gear. With the gear cover off, you also have the option of using a 93-tooth gear. Anything larger than a 93-tooth gear will not fit at all due to the fact it will contact the output yokes for the axles. Contact will occur whether you are using the stock yokes, CVD's, or the Traxxas steel yokes.

Also it should be noted that RPM states that their aftermarket gear cover is not recommended for use with spur gears larger than 87-teeth. So running the RPM cover may limit your gearing possibilities when compared to the stock setup.

Part One:	How To Gear Your Motor
Part Two:	Determining Gear Size
Part Three:	Gear Ratio Calculator