Gearing is an essential factor to extract the maximum potential of your motorcycle – be it for performance or smooth riding.
Unfortunately, this knowledge is lost among many current motorcyclists. Any race team will tell you that the wrong gearing selection will have their rider either struggling with acceleration, or deceleration, or cornering speed, or rear tyre traction, or all of these.
What is “gearing”?
Gearing alludes to the gear ratios. Gear ratios influence the translation of the gearbox’s torque output to the driving wheel. But to simplify, gear ratios influences how your motorcycle accelerates, decelerates (through engine braking), cornering speed, and traction.
Race bikes and sportbikes have “cassette-type” transmissions that can be pulled out quickly and lets the race technician change the sizes of individuals gears inside, in addition to the final drive gearing. We on street bikes, on the other hand, rely on altering the final drive gearing.
By the way, final gearing means the relation between the front and rear sprocket sizes. Gear sizes are determined by the number of teeth.
How does it work?
Gear ratio is calculated by diving the size of the rear sprocket with the front sprocket. For example:
Front sprocket size: 15 (teeth)
Rear sprocket size: 46
So, the ratio = 46 / 15 = 3.066 ≈ 3.07 : 1 (read as 3.07 to 1)
Meaning, the rear sprocket turns 3.07 times in order for the rear wheel to turn once.
Shorter gearing
To illustrate this easier, let us take another example but based on the above.
We keep the front sprocket size the same: 15
We replace the rear sprocket to a bigger one: 50
So, the new ratio is = 50 /15 = 3.33 : 1
Thus now, the sprocket needs to turn more to rotate the rear wheel once around. As such, more engine is required. This known shorter gearing (point below).
From the seat:
- The motorcycle now accelerates faster.
- Engine back torque (engine braking) is more pronounced when we roll off or shut the throttle.
- The bike slows down much faster.
- Throttle changes result in more abrupt power delivery.
- It can also make the bike feel heavier to steer through corners as speed rubs off much quicker.
- Resorting to using a higher gear for corners may result in freewheeling into the corner which scares many riders.
- Shorter gearing results in more engine vibrations during cruising due to the higher revs.
- Fuel consumption is increased due to higher engine RPM at a given speed.
- This is called shorter gearing, as the top speeds achievable by each gear is now lower due to engine needing higher RPMs to turn the rear wheel.
- Shorter gearing is great if you stay in an area with many sharp and short corners, such as Ulu Yam, or if you are riding at a track with short corners and straights such as the old Batu Tiga Circuit.
Longer gearing
Let us explore the other end of the spectrum.
We keep the front sprocket size the same: 15
We replace the rear sprocket to a smaller one: 40
So, the new ratio is = 40 /15 = 2.666 ≈ 2.67 : 1
With this change, the sprocket needs to turn more to rotate the rear wheel once around. As such, more engine is required. This known longer gearing (point below).
From the seat:
- The motorcycle now accelerates slower.
- Engine back torque (engine braking) is less pronounced when we roll off or shut the throttle.
- The bike takes longer to slow down.
- Throttle changes result in smoother power delivery.
- It can also make the bike feels easier to steer through corners as more speed is maintained.
- The rider may resort to using a lower gear for corners for more stronger engine braking.
- Longer gearing results in less engine vibrations during cruising due to the lower revs.
- Fuel consumption is reduced due to lower engine RPM at a given speed.
- This is called longer gearing, as the top speeds achievable in each gear is now higher as the engine needs fewere RPMs to turn the rear wheel.
- Longer gearing is great if you stay in an area where you need to commute on highways.
- Likewise, you can change to a longer gearing if you are going on a long-distance tour which covers highways.
- Longer than stock gearing also benefits motorcycles with engines modified for more power.
- However, longer gearing results in sluggish acceleration from a standstill, and overly long gearing requires slipping the clutch to avoid stalling the engine.
Front vs. Rear Sprocket
Replacing the rear sprocket is an easier and quicker job as it is attached to the exposed rear wheel, compared to the front sprocket which is hidden behind a cover.
However, replacing the front sprocket for gearing ratio changes is better as the chain does not need to wrap around a small circumference.
Then again, certain motorcycles may not have enough space to permit a larger front sprocket.