Transmission and Rear Sprockets

Transmission and rear wheel sprockets

The smaller chain sprocket is located on the transmission and the larger one on the rear wheel, so that the rear wheel turns more slowly than the transmission shaft. With this ratio, the transmitted torque is increased.

So, what is the drive ratio?

The smaller the front sprocket and the larger the rear one, the greater the gear ratio and the faster the Harley sprints off a red light — we suppose that in our test races the engine and transmission are always the same — but there will be a loss in top speed. Conversely, depending on the available space, you will either increase the size of the front sprocket or choose a smaller rear sprocket to allow the motor to run at higher road speeds while keeping engine speed down. And just note: on any gear ratio change, possibly the chain lenght (numer of links) can vary, too. You may shorten th chain quick and dirtily with chain breaker tool. But lengthening it with an additional master link and a few links that you find in your grab box is only for the absolutely fearless or in emergency cases. You better choose a new and longer drive chain.

Whe is it time to replace the sprockets? How does one notice sprocket wear?

There are many motorcyclists who always replace the whole drive train: chain, front and rear sprockets. This way, they are on the safe side. according to some motorcycle manufacturers this is even mandatory.

In the workshop manuals for FL and FX models from 1978 to 1984 — just as an example — the maintenance plan doesn't mention sprocket or chain replacement at all, at first. Every 2,500 miles, the parts should be checked and the chain should be tightened if necessary. Sprockets — as we read in the rear sections of the manual — are replaced if necessary and when the teeth show a distinct hook shape. Called “shark teeth” by some.

By the way: our replacement sprockets – which we are happy to get from PBI in Oregon, USA – are without exception made the way that they can be swapped for the originals on a one-to-one basis.

So, what is an offset sprocket?

If you replace the rear wheel with a wider one, the chain line will alter. To move the chain line outwards (to the left on the big Twin, to the right on the Sportster), you will need a transmission sprocket with appropriate lateral offset (and maybe a longer main shaft, too). Then, on the wheel, the appropriate rear sprocket. We recommend our universal rear sprockets and additionally an offset adapter made of aluminum. The dimensions are available in our shop, and of course we are there to provide you appropriate information by email or phone.