What Do The Primary And Secondary Drives On A Harley-Davidson Do?

A motorcycle’s engine makes the power to move it, but that power has to go through a few different parts before it gets to the rear wheel. The transmission, clutch, chain, belt, and sprockets all play a part in that process. Now, when someone says “motorcycle”, likely the first brand that comes to mind is Harley-Davidson. There have been many iconic Harley-Davidsons through the decades, and one of the staples of the company is the use of primary and secondary drives.

Basically, the primary and secondary drives work together to form the drivetrain, as they send power from the engine to the rear wheel while adjusting the gearing to boost torque. The primary drive carries power from the engine’s crankshaft to the clutch and transmission. On many Harleys, that’s 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. That chain turns the clutch assembly, and when the clutch is engaged, it passes the power along to the transmission input shaft. Think of the primary drive as the first link between the engine and gearbox.

On the other hand, the secondary drive moves power from the transmission to the rear wheel, and it’s sometimes referred to as the final drive. Nowadays, most modern Harleys use a belt for the secondary drive. The transmission’s output shaft spins a small front pulley, which turns a toothed belt connected to a bigger pulley on the rear wheel. As that back pulley spins, the rear wheel then starts to turn. Nevertheless, some Harley-Davidson models use a chain for the secondary drive instead, but the basic principle stays the same.

Along with the transmission, the primary and secondary drives set the motorcycle’s overall gear ratio, which shapes acceleration and engine RPM. A lower gear ratio usually means higher road speeds for the same engine RPM, whereas a higher number boosts acceleration. That being said, the primary and secondary drive ratios stay fixed during normal riding, while the transmission supplies different ratios as you shift.

Some Harley-Davidson models are perfect for everyday use, though riders have the freedom to change how a Harley-Davidson performs by swapping in larger or smaller pulleys and sprockets. What can actually be installed depends on how the specific motorcycle is built, and it’s important to note that any such change comes with certain trade-offs. For instance, setting up the Harley for quick, hard acceleration means giving up smooth and easy highway cruising. Conversely, gearing it for relaxed cruising will make the motorcycle feel slower and less responsive when you twist the throttle. These choppers are undoubtedly special, so pay attention to some of the most important tips for new Harley-Davidson riders that will keep you safe and your rides thoroughly enjoyable.