Stay Upright - Gears & Gear Changing

Firstly, I'll deliver a bit of a primer on what your gears actually are and what they do. Gears are simply toothed wheels that deliver the power from the engine to the back wheel. Most modern motorcycles have five or six gears.

The reason motorcycles have gears is really quite simple. Each gear wheel is of a different size and provides a different ratio between engine revolutions (measured in revolutions per minute, or RPM) to back wheel revolutions. When riding in, say 4th gear for example, at a given RPM, the rear wheel will turn more times than when riding at the same RPM in 1st gear.

Imagine if we only had a single gear. Our lowest speed would be limited by how slowly our engine could rev without stalling, and our top speed by how fast it can spin without blowing up. Having gears means we can always select the correct ratio of engine RPM to rear wheel revolutions, or road speed.

However, speed is not the only thing that helps to decide which gear to select. The load on the engine can change as well. When riding up a hill, for instance, the load on the engine is greater than it would be on level ground. So, to keep a constant speed on the flat and up the hill, we select a lower gear. Anyone who has ever pedalled a pushbike on undulating ground will have a good understanding of the need to be in the correct gear for the hill to be tackled effectively.

To smooth out the power delivery from the engine via the gears to the rear wheel, the motorcycle also has a clutch. Without the clutch, moving off, coming to a stop, and changing gears would be jerky at best, and dangerous, if not impossible, at worst.

We all know the clutch is operated by a lever at your left hand, but how many of you know the internal workings of your bike's clutch once you squeeze that lever? Think of the clutch as two circular plates spinning on the same axis. Strong springs press them together and your hand lever pulls them apart. The 'driving plate' of the two is joined to the engine crank. The 'driven plate' is joined via the gears and chain to the rear wheel. When you pull in the clutch lever, you separate the clutch plates, disengaging the drive to the rear wheel. As you slowly ease the clutch lever out, the driven plate presses progressively harder against or "clutches" the driving plate. At first, they slip against each other, but as you keep releasing lever pressure, and as the bike moves, the plates eventually stop 'slipping' and friction locks them together, so they spin at the same speed. This is how power is smoothly delivered to the rear wheel. Harsh clutch operation by the rider can cause jerks and stalls.

So, how and when do we actually operate gears and clutches? Watch out for the next issue when I will explore the systems required to be a silky-smooth rider.

Until next time (and part 2 of this article) Stay in the right gear.

Dave Gibson

State Manager ACT

Stay Upright

Motorcycle Techniques