Chain and sprocket kits: pitch, links and tooth counts explained

Ordering a chain kit is easy when you know three numbers: the chain size, the number of links and the sprocket tooth counts. Get any of them wrong and the kit will not fit — or it will fit and change how the bike rides.

What 520, 525 and 428 mean

The first digit is the pitch (the distance between pins) in eighths of an inch. The last two digits are the roller width in eightieths of an inch.

A 520 and a 525 chain have the same pitch but are not interchangeable: the sprocket teeth are a different width.

Counting links

Count pins, not plates, and include the connecting link. Most kits are supplied at the standard length for the bike; if you change gearing by more than a couple of teeth you may need to add or remove links.

Changing the gearing

As a rough guide, one tooth fewer on the front sprocket has about the same effect as three teeth more on the rear. Both make the bike accelerate harder and rev higher on the motorway. Remember that a gearing change also changes the speedometer reading on bikes that take their speed from the front sprocket.

Why kits, not just a chain?

A worn sprocket has hooked, pointed teeth that have stretched to match the old chain. A new chain on old sprockets wears out in a fraction of its normal life. Replace all three together.

Keeping it alive

• Set slack to the figure on the swingarm sticker, measured at the tightest point of the chain.
• Clean and lube every 500 miles, more often in winter. Lube the inside run of a warm chain.
• Rivet-type connecting links need a proper riveting tool. Clip links are fine on 125s — with the closed end facing the direction of travel.