HOW LOSING OR ADDING A FEW TEETH CAN IMPROVE YOUR BIKE’S PERFORMANCE
No other final drive design has the gearing flexibility of a chain-drive system. By simply swapping out that stock front or rear sprocket with a different size, you can tune your bike’s performance to your distinct riding style and preferences.
Why change gearing?
Racers routinely change gear ratios to maximize speed and performance for each particular track. For the rest of us, a gearing change can enhance specific performance characteristics, like acceleration or fuel economy—and even subduing an annoying engine vibration.
There are two components of the chain-drive system that can be easily changed to modify your bike’s performance.
- The Countershaft Sprocket. This is the small, toothed sprocket connected to the transmission output shaft
- The Rear Sprocket: the large sprocket mounted to the rear wheel
Changing the size of one or both of the sprockets is all it takes to modify the relationship between engine speed and rear wheel speed: what’s known as the gear ratio.
So, what’s a gear ratio?
The final drive ratio represents the number of times the transmission’s output shaft rotates for each complete revolution of the rear wheel. To determine the ratio, simply divide the number of teeth on the rear sprocket by the number of teeth on the countershaft sprocket. Boom! That’s all there is to it.
45-tooth rear sprocket ¸ 17-tooth front sprocket = gear ratio of 2.65
In this example, the transmission shaft rotates 2.65 times for each rear wheel rotation.
Go high or go low?
You have two options when deviating from your bike’s current gear ratio; go higher with the gearing or go lower. What does that mean?
- Higher gearing more closely matches rear wheel speed to transmission shaft speed, resulting in lower engine RPMs, higher potential top speed and improved fuel economy. The tradeoff is reduced throttle response and acceleration. Higher gearing will have a lower ratio number than your current setup.
- Lower gearing delivers more rotation of the rear wheel for each spin of the countershaft, thereby raising engine RPMs and improving throttle response for quick acceleration. The compromise is lower top speed and fuel economy. With lower gearing, the ratio will be a higher number.
Front teeth or back teeth?
Adding teeth to the front and rear sprockets have opposite effects. Installing a larger countershaft sprocket creates higher gearing, while a larger rear sprocket lowers gearing. Similarly, a smaller front sprocket lowers the gearing while a smaller rear sprocket makes gearing higher.
So, which sprocket should you change to achieve the effect you want?
- For taller gearing, a one-tooth-larger countershaft sprocket is often the best bet. For more subtle changes, combine that plus-one-tooth front sprocket change with a minus-one-tooth change at the rear sprocket.