Harley-Davidson motorcycles use primary and secondary drives to form the drivetrain, working together to send engine power to the rear wheel while adjusting gearing to boost torque. The primary drive connects the crankshaft to the transmission, while the secondary drive delivers that power from the gearbox to the rear wheel.
How the primary drive moves power
While an internal combustion engine generates the energy needed to propel a motorcycle, that output must travel through several components before reaching the back wheel. The transmission, clutch, chain, belt, and sprockets all play a part in that process.
When someone says “motorcycle”, likely the first brand that comes to mind is Harley-Davidson. Throughout the decades, numerous legendary Harley-Davidsons have emerged, and relying on primary and secondary drives remains a hallmark of the manufacturer.
Essentially, the drivetrain is built by the combination of primary and secondary drives, which transmit energy from the powerplant to the back wheel while modifying the gear reduction to increase torque. The primary drive carries power from the engine’s crankshaft to the clutch and transmission.
On many Harleys, that is done with a chain and sprockets tucked behind the primary cover on the motorcycle’s left side. When the engine runs, the crankshaft spins the engine sprocket, which drives the primary chain.
The clutch assembly is rotated by that chain, and releasing the clutch lever sends the energy onward to the transmission input shaft. Think of the primary drive as the first link between the engine and gearbox.
What the secondary drive does
Conversely, power is transferred from the gearbox to the rear wheel via the secondary drive, occasionally called the final drive. Nowadays, most modern Harleys use a belt for the secondary drive.
A compact front pulley is rotated by the transmission’s output shaft, driving a notched belt that links to a larger pulley on the back wheel. As that back pulley spins, the rear wheel then starts to turn.
Alternatively, a few Harley-Davidson versions employ a chain for their secondary drive, though the underlying mechanics remain consistent, SlashGear reported.
How drive ratios affect performance
Working alongside the gearbox, the primary and secondary drives establish the bike’s cumulative gear ratio, influencing both acceleration and engine speed. Higher speeds at a given engine speed are typically achieved with a lower gear ratio, whereas a higher number boosts acceleration.
Even so, the primary and secondary drive ratios stay fixed during normal riding, while the transmission supplies different ratios as you shift. While certain Harley-Davidson models are ideal for daily commuting, operators retain the ability to alter a Harley-Davidson’s performance characteristics by installing alternative pulley and sprocket sizes.
What can actually be installed depends on how the specific motorcycle is built, and it is important to note that any such change comes with certain trade-offs.
As an example, configuring the Harley for rapid, aggressive acceleration sacrifices effortless highway touring. On the other hand, optimizing the gearing for casual cruising results in a motorcycle that feels more sluggish and less reactive when applying throttle.
Keeping you secure and ensuring your journeys remain thoroughly fun requires heeding key guidance for novice Harley-Davidson operators, given that these custom machines are undeniably unique.
