SRAM / Sturmey Archer / Shimano sprocket / chainwheel for hub gears and back pedal brakes

These sprockets fit on most back pedal brake hubs and hub gearing systems from SRAM, Sturmey Archer, KMC and Shimano - all those which use the three splines method of mounting.

The life-span of these parts is normally very long, but a worn sprocket promotes wear of your chain, so it is best to replace them when they look worn.

You can also change the sprocket to adjust your gearing ratios. Fitting a larger sprocket will reduce the gearing on your bike, making starting off and climbing hills easier. Fitting a smaller sprocket increases your ratios, making it easier to ride at higher speeds.

On three speed bicycles, I like to have the middle gear (number two) as the one I normally use as this is the most efficient of the three. By adjusting the sprocket size it is possible to arrange that most of your time is spent in the middle gear, leaving bottom gear for setting off, climbing hills or stiff headwinds and top gear for downhill or when riding with a tailwind. If you live in a hilly area, it may be worth setting up your bike so that the top gear is best for cruising on the flat while 1 & 2 give two options for climbing hills.

Some of the sprockets are made by the manufacturers named in the title, some are generic products which have no manufacturer's mark. All are functionally identical.

Please choose a 2.1 mm or 2.9 mm wide sprocket depending on the width of your chain, and either a dished or flat sprocket depending on what is required to keep your chainline correct. All sprockets have a 35 mm hole in the middle and are held in place by three prongs. See additional images for a photo.

Old incompatible hubs
Note that all the sprockets we sell use circular teeth which are compatible with the standard set by Sturmey Archer. All hub gears and back pedal brakes from all manufacturers that we're aware of have for decades used compatible splines and will work with these sprockets. However there also exist very old hubs, many decades old, which use different types of splines. These look similar and they have similar dimensions are close, but they are not compatible. For instance, some very old Sachs hubs require sprockets with rectangular teeth, other very old hubs require six teeth. If you fit the sprockets that we sell to those hubs then it is likely that the teeth on the sprockets will fail due to poor fit on an incompatible hub. Otherwise you can expect a long lifespan from the sprockets that we sell.

Calculating sprocket size
If you're trying to achieve lower gearing on your bike, choose a new sprocket with more teeth. If you're trying to achieve higher gearing then pick a sprocket with fewer teeth. If you're trying to achieve a particular ratio in gear inches then the formula sprocket_teeth = chainwheel_teeth / desired_gearinches * wheel_size_inches will give the number of sprocket teeth required, at least for the middle (straight through) gear on 3 speed hub gears or on a single speed setup.