Can you point to the drivetrain on your motorcycle? Probably not – and you’re about to find out why.
In this blog post, you’ll discover:
– What the “drivetrain” is
– The 3 parts of the drivetrain
Prefer to get this information in podcast form? Listen to the 30 Minute Motorcycling Podcast episode about the drivetrain:
What is the “Drivetrain?”
To go back to the original question at the beginning – do you know why you can’t point to your drivetrain?
That’s because it’s not a standalone component like your clutch, brake lever, or wheels.
Instead, it’s a collective term for every component that delivers power from the engine to the wheels.
On a motorcycle, the drivetrain is separated into three groups:
- Primary drive
- The transmission
- Final drive
Each of these groups represents a stage in the power transmission process as it travels from the engine to the rear wheel.
We’ll go over each one in more detail.
The primary drive consists of parts that deliver power from the crankshaft to the transmission and includes:
- Clutch and clutch assembly
- Engine output sprocket
The clutch assembly
The clutch assembly houses the clutch, which engages and disengages power from the engine to the rear wheel to change gears.
Without the clutch, the only way to change gears would be to come to a complete stop.
Coming to a complete stop would be fine for first or maybe second gear but difficult (if not impossible) for anything above fourth gear.
Most motorcycles use a “wet-clutch” – meaning that the clutch transfers its power through mechanical and fluid couplings.
This fluid makes the clutch much more smooth since the lubricant dampens any fierce engagement from the clutch. Furthermore, a wet clutch is also less likely to burn out.
For more information about the differences between a dry and wet clutch, watch this video from Motorcyclist Magazine, where Ari Henning sums them up in just 3 minutes:
The engine output sprocket (if chain-drive)
The engine output sprocket is a small toothed wheel that engages with the drive chain or belt. Typically, the engine output sprocket sits on your wheel.
The transmission is a complex topic worthy of its article, but we’ll stick to the basics for now.
Once the power has reached the transmission, it must be transferred (or “transmitted,” hence the name) to the rear wheel in a controlled manner.
A transmission can be either manual or automatic, which handle the gear changes either through a clutch lever or a torque converter.
For a more detailed overview of a motorcycle transmission, check out this video from Cycle World:
Regardless of whether the transmission is manual or automatic, they both contain a set of gears to handle the gear changes.
The CVT Transmission – A Slight Exception
Unlike manual and automatic transmissions, CVT transmissions don’t have any gears.
Instead, the gear changes are handled through two pulleys and a belt – which function as one “long gear.”
But regardless – the power from the engine still goes through a CVT transmission, just like a conventional one with gears.
Want to know more about how a CVT transmission works? Read the blog post about it here on The Dual Wheel Journey:
The Final Drive
As the name suggests, the final drive represents the final part of the power transmission process.
Some two-wheelers might not have a final drive at all. For example, many scooters handle the final gear reduction through a pair of gears considered a part of the gearbox.
Because of this, these gears are NOT considered to be their own drive.
Motorcycles, on the other hand, have a final drive – which depending on the model is either:
- Drive chain
- Drive belt
- Shaft drive
The most common final drive for motorcycles, chain drive, consists of a chain that is attached to the rear wheel sprocket at one end and another sprocket in the gearbox at the other.
This type of final drive is lightweight and cheap, but since the chain is out in the open, you must lubricate it often to transfer the power effectively.
A drive chain can be of the following type:
- Standard roller chain
Motorcycles with belt drive use a toothed belt typically made from kevlar, which connects to the rear wheel, just like a chain.
Since the belt isn’t exposed in the open, it doesn’t require as much cleaning and maintenance as a chain. It’s also much quieter.
Want to know more about the differences between chain and belt drive? Read the Dual Wheel Journey blog post about it:
But we’re not done just yet, because there’s a third type known as “shaft drive.”
A shaft drive consists of a large shaft, (similar to the drive shaft on a car) that is attached to the gearbox on one end, and to the rear wheel on the other end.
Many bikes from BMW use shaft drive (including the R32 pictured above).
Just like belt drive, shaft drive requires very little maintenance. But it’s also expensive to make, which is why shaft drive motorcycles tend to be expensive to buy.
Shaft drive also increases the amount of unsprung weight – i.e. weight that isn’t supported by the suspension.