Are you a city rider with untapped top-end power in your bike which you would happily trade for more low-end acceleration? Or are you a regular roadster who can use a bit more top speed on those highways and don’t really care about low-end torque? Being bike enthusiasts, it is hard for us to stay satisfied for long. And the easiest way to tune our engine output to match individual riding styles and necessities is adjusting the final drive ratio with simple swaps of sprockets.
Time to get technical
The measurement of sprockets or chainwheels is done by the number of teeth on them. And the final drive ratio is calculated by dividing the rear sprocket by the countershaft or front sprocket size. Let’s say your bike has 46T (tooth) rear sprocket and 14T front sprocket. By dividing them we can easily calculate the final drive ratio of your bike which is 3.29, meaning the front sprocket of your bike rotates 3.29 times for your rear sprocket to make a complete rotation. Now if you change your rear sprocket into 45T and front sprocket into 15T, the ratio will change to 3.00. This means the front sprocket will have to revolve 3 times for the rear sprocket to revolve once. And it’s called Gearing up. Gearing up will add more top speed to your bike, but on the other hand, will decrease the acceleration of your bike in the low-end (because of decreased torque).
Now, what if you want to go all “dragster mode” on the street and ready to sacrifice some top speed to get more low-end acceleration? In that case, you need to “Gear down”. Let’s do the calculation. If you swap your 46T rear sprocket with 48T and 14T front sprocket with 13T, the final drive ratio will increase to 3.69. Which will decrease your top speed but in return increase your initial acceleration because of increased torque on the rear wheel.
An easy way to remember the outcome of Gearing up (higher ratio number) and Gearing down (lower ratio number) is, Gearing Up increases top speed- decreases acceleration. On the other hand Gearing Down decreases top speed- increases acceleration. Now all you need to do is determine your necessity in accordance with your riding style and road condition. Then again, for your convenience, here is a chart of gear ratios and their outcomes:
Now hold up
There are a few things you need to note down before you rush to change your sprockets. Make sure your workshop has the necessary kits to recalibrate your speedometer because changing the final drive ratio of your bike will mess up your speedometer, unless you are lucky and your bike has a front wheel speed sensor.
Another important point is, even though for example I changed the teeth count of the front sprocket, it is always recommended not to use smaller than stock front sprocket as it increases chain friction and decreases the life expectancy of both sprockets and chain.
This article originally appeared in MotorAid Bangladesh. It is being published here under special arrangement with Dhaka Tribune. To know more about MotorAid, check them out on Facebook