Chain

A BMX chain is the single-speed roller chain that connects the sprocket on the cranks to the driver on the rear hub. It carries your pedalling force to the back wheel.

What it does

The chain wraps around the sprocket and the rear driver. When you push the pedals, the chain pulls the driver and turns the rear wheel. Because a BMX has one gear, the chain has no derailleur to manage and no shifting. Its job is simple, but it takes a lot of load from sprinting and hard landings.

A worn or badly set up chain skips, falls off or wears out the sprocket and driver.

Types and standards

Pitch and width

All BMX chains use 1/2 inch pitch, the spacing between pins. The width, which is the space between the inner plates, varies.

Width	Used with	Notes
1/8 inch	Wide single-speed sprockets and drivers	The standard for BMX. Tough and widely available.
3/32 inch	Narrow sprockets and drivers	Lighter and found on some parts. Not interchangeable with 1/8 inch.

A 3/32 inch chain on a 1/8 inch sprocket can slip or jump. A 1/8 inch chain on a 3/32 inch sprocket will not fit. Always match your sprocket and driver.

Half-link chains

A standard chain has alternating inner and outer links, so its length changes in pairs of links. A half-link chain uses offset links, so you can add or remove a single half inch at a time. That lets you set tension closer to ideal without moving the wheel too far in the dropouts.

Half-link chains are common on BMX bikes because dropout adjustment is limited, so being able to change length by a single link helps. Check the product listing to see which type you are buying.

Master links

A master link (or connecting link) lets you open and close the chain without a chain tool. Most are a clip-on or snap-on plate. Some chains need a chain tool to join the ends. Always use the master link made for your chain width.

Sizing and compatibility

1. Width: match your sprocket and driver (1/8 inch or 3/32 inch).
2. Length: the chain must reach around the sprocket and driver with a bit of slack.
3. Rear wheel position: your frame's dropouts decide how much the wheel can move. See frame geometry.
4. Chainline: the sprocket and driver should line up. Use spacers or bottom bracket changes if not. See bottom bracket.

Chain tension

Pull the rear wheel back until the chain is snug. You should see a small amount of up and down play in the middle of the chain, around a centimetre. Spin the cranks and check the tension at different points, because an out-of-round sprocket can make it tighter in one spot. Make sure the chain still has some play at its tightest point.

Tensioners

Chain tensioners (often called tugs or chain tensioners) mount at the dropouts and push the axle back to stop the wheel pulling forward. They hold the wheel in position and make it easier to set the chain tension evenly. Many riders use them to keep the wheel straight after hard landings.

How to choose

1. Pick the width first. Most riders use 1/8 inch.
2. Choose a half-link chain if your rear wheel has limited adjustment.
3. Buy a chain with a master link if you want easy removal.
4. Pick a coated or nickel-plated chain for wet conditions.
5. Budget chains work fine for casual riders. Better chains cost more and last longer, so heavy riders see a bigger benefit.

When to replace

A chain stretches as the pins and bushes wear. A stretched chain wears sprockets and drivers faster. To check, measure 12 full links (24 half-inch pitches, counting inner and outer links), which should be exactly 12 inches pin to pin when new. At about 12 1/16 inches, replace the chain. If it has reached 12 1/8 inches (about 1 percent), the sprocket and driver are probably worn too and may need replacing with it. Also replace it if links are stiff, rusty or cracked, or the chain skips under load.

Replace the chain, and check the sprocket and driver, at the same time. See how to fix a BMX chain.

Maintenance

• Wipe the chain and apply a light lube after wet rides.
• Do not over-oil, because oil attracts grit.
• Check the tension monthly.
• Look for stiff links, which cause skipping.
• Remove the chain before cleaning the rear hub or sprocket.
• See BMX maintenance basics.

Related parts

Sprocket, cassette hub, freecoaster hub, cranks and bottom bracket.