Motorcycle Gearing - What you Need to Know

A lot of people read the specifications of there motorcycle and see primary and final drive, but they have no clue what it really means. The primary drive (internal) gear ratios of a motorcycle can be adjusted by the manufacturer during the design stages of the motorcycle or by top-tier race teams with the judicious application of money. Changing the primary drive ratios isn't feasible for regular guys, but the opposite is true for the final drive. The final drive is composed of the countershaft and rear sprocket. It's the cheapest way to make significant changes to a motorcycle's power delivery.

Gearing terminology can be a bit confusing. Going to a smaller rear sprocket or larger countershaft (front) sprocket is referred to as 'gearing it up' or 'going taller.' Taller gearing means bigger gaps between gears, less hit and faster top speeds. It creates a broader, mellower-feeling powerband that's easier to ride and requires less shifting. Conversely, a bigger rear sprocket or smaller countershaft sprocket is known as 'gearing it down' or 'going lower.' Adding teeth to the rear and losing teeth on the countershaft translate into a quicker-revving, narrower-feeling, harder-hitting powerband that requires more shifting but less clutch use.
If you have experience with a bicycle's derailleur, the concept of gearing should be intuitive. You shift to a bigger gear on the rear to get more torque for steeper inclines, and you shift to a smaller ge3ar on the rear for higher speeds. The opposite is true for the front sprockets at the cranks. And, as with bicycles, changing gears on the front sprocket makes a bigger difference than changing gear on the rear. When you get confused, think about a mountain bike.
  • Too Low? On a bicycle, when you're in a low gear going downhill, your legs immediately spin out and can't keep up. When your motorcycle gearing is too low, the engine does the same thing. It quickly revs through the useful part of the powerband and you have to upshift immediately. If you've installed a big-bore kit or significantly increased your motorcycle's power, it will be geared too low.
  • Too tall? When you're in too tall a gear on a bicycle, it's difficult to pedal, and it takes a long time to get on top of the gear. You need to be in the right gear to maximize the potential of your legs. The same is true with a motorcycle. If you're going up a hill or are heavy loaded, your engine will lug to pull the gear and you might have to downshift.
For final drive ratios. As a rule of thumb, one tooth on the front countershaft sprocket equals approximately three on the rear sprocket. To make a precise comparison, translate the gearing into ratios by dividing the number of teeth in the front by the number of teeth in the rear. A smaller ratio number is taller gearing. For example, a 51/14 gear ratio is 3.64, but a 48/13 is a 3.69 ratio.

Before you put on a larger rear sprocket, you must pay close attention to how much chain adjustment you have available in the rear axle. A bigger rear sprocket might require a slightly longer chain, or with a smaller sprocket your chain will maybe be too long.

Never mate a used chain with a new sprocket or vice versa. Yes, I know some mechanics disagree, but trust me. The pitch between the teeth of a new sprocket and links of a new chain is the same, but a used chain or a worn sprocket has a different pitch. The discrepancy will damage both parts. Also, make sure the sprocket bolts are tight. Loose sprocket bolts ovalize the holes in the hub. After that happens, the sprocket bolts will come loose constantly, or worse, throw the chain, motorcycle and the rider.
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