Chains

BMX race chains: width, length and tension

This is the hardest-working part of the drivetrain and often the least watched. Every watt produced out of the gate passes through the thirty or so rollers in mesh, on a single gear with no derailleur to absorb the shock loads. A chain in the right format, correctly tensioned, goes unnoticed; the wrong one jumps under the first pedal stroke.

1/8" or 3/32": the width that decides everything

All BMX chains share the same 12.7 mm (1/2") pitch, but not the same internal width. The 1/8" measures 3.18 mm between the plates and remains the historic BMX race standard: strong, forgiving, made for thick teeth. The 3/32" drops to 2.38 mm, saves a few tens of grams and requires tooth profiles designed for it at both ends. The two formats do not mix: a 3/32" on 1/8" teeth floats sideways, while a 1/8" on 3/32" teeth never seats properly.

Full links and half-links

A conventional chain alternates inner and outer links, so it can only be adjusted in 25.4 mm steps. A half-link chain is built from identical, fully interchangeable links, which lets you set the length in 12.7 mm steps. That matters on a frame with short dropouts, or when a one-tooth cog change leaves the wheel jammed at the end of its travel.

Chain length and tension

Chains ship long, between 98 and 112 links depending on the model, and are shortened during the build with a chain tool. Set the wheel position in the dropouts first, then cut: the right length is the one that leaves the wheel roughly in the middle of the adjustment range. For tension, aim for about a centimetre of vertical movement in the middle of the top run. Too tight and the chain drags and wears out the hub bearings; too slack and it derails coming off a jump. A chain tensioner locks the setting in place on horizontal dropouts.

Compatibility with the chainring and the cog

The chain has to match the tooth thickness of your chainring or your one-piece sprocket at the front, and that of your rear sprocket — all three parts necessarily share the same format. Then check the alignment: the chain run should sit parallel to the chainstay, which is corrected with bottom bracket spacers rather than by forcing the chain over.

Materials and finishes

Plates are heat-treated steel, sometimes nickel-plated or chromed to resist corrosion, with hardened pins and ground rollers. Higher-end versions save weight by cutting away the side plates and refine roller geometry to reduce friction. Coloured finishes exist in both 1/8" and 3/32" to tie the drivetrain in with the rest of the build.

Wear and replacement

A chain elongates in use: beyond roughly 0.75% elongation, measured with a wear gauge, it starts hollowing out the teeth of the cog and the chainring. Changing it in time costs far less than replacing the tooth profiles as well. Clean it after muddy motos, lubricate sparingly and wipe off the excess: too much lubricant holds track dust and speeds up wear.

The BMX RACING advice

Give us the format of your teeth and the rider category: we point you to the right width, the right link count and the right connector, along with a chain tool if you are missing one. Dispatched within 24 to 72 hours, you can spread the cost over 2 or 3 payments with Alma.