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- What the transmission does – and why you need gears
- The 2 most common types of manual motorcycle transmissions
- The definition of “gear ratios” – and how to calculate gear ratio easily
Prefer to get this information in podcast form? Listen to the 30 Minute Motorcycling Podcast episode about the motorcycle transmission and gear ratios:
The Motorcycle Transmission – What Does It Do?
The motorcycle’s transmission contains a series of gears – hence why the transmission is often called the “gearbox.”
Each gear has two gears fitted to the input shaft and a corresponding one on the output shaft.
The engine turns the input shaft, while the output shaft sends the power transferred through it to the bike’s rear wheel.
When you select a gear, it locks in place to the shaft it sits on.
Anyway, the lower the gear, the faster it rotates. And the faster the gear rotates, the more power you’ll have.
Compare the acceleration you’ll get when you’re in first gear and compare it to third, fourth, or even fifth gear, and you’ll see what I mean.
A modern motorcycle transmission is usually “constant mesh” – meaning that no matter if they’re selected or not, the gears constantly mesh together with each other.
Before the constant-mesh gearbox, motorcycle transmissions used to have sliding rotating pinions that moved back and forth to change gears.
However, this setup meant that the gear changes tended to be unsmooth, and if you missed a gear, it resulted in the most dreadful noise – hence why these gearboxes were often called “crash gearboxes.”
Why do you need gears?
Instead, power is delivered through a metal cable that tensions as you squeeze the brake lever - similar to how many motorcycle clutches work.
Although not so much on modern motorcycles, these brakes are highly common on bicycles and e-bikes.
The 2 Most Common Components of a Manual Motorcycle Transmission (Apart From the Gears)
1. The clutch
Would you like to discover more about what a motorcycle clutch consists of, and what the “clutch friction zone” is?
Check out the article about it here on the Dual Wheel Journey.
2. Gear selector mechanism
- A selector drum
- A gearshift arm
- Two selector drum pins
- Selector forks (one for each pair of gears)
What Does “Gear Ratio” Mean?
- The input shaft rotates 3 times faster than the output shaft
- The output shaft has 3 times more gear teeth than the input shaft
Gear ratio equation – calculate your gear ratio easily
Motorcycle Transmission & Gear Ratios – In Conclusion
- The transmission’s job is to transfer the power from the engine to the wheels
- The gears are needed to adapt the power transfer depending on the situation
- To change gears, the engine must be disconnected from the rear wheel – which is the purpose of the clutch
- “Gear ratio” refers to how much faster the gear on one shaft rotates and how many more teeth it has compared to the other gear