- Chain slack changes as the suspension moves. Set it at the tightest point in the travel, not on the stand.
- Too tight is worse than slightly loose. A tight chain loads the output bearing and the shaft every rotation.
- Check wear by pulling the chain off the back of the rear sprocket. If you can see daylight through a tooth, it is done.
- Replace the chain and sprockets together. A worn chain destroys a new sprocket in a handful of rides.
- Clean first, then lube. Lubing a dirty chain makes grinding paste.
A chain is a consumable. It stretches, it wears, and eventually it takes the sprockets with it. What decides whether that happens at 800 miles or 2,500 is about ten minutes of attention spread across the season.
Why slack matters
On a bike with rear suspension, the distance between the countershaft and the rear axle is not fixed. It changes through the travel, and there is one point in that arc where it is longest and the chain is tightest. Set slack with the bike on a stand and you are setting it at a point the bike almost never sits at.
A chain that is correct on the stand and bar-tight mid-travel is the single most common drivetrain mistake we see, and it is why people replace output bearings early.
Setting slack
- Socket for the axle nut and the adjuster locknuts
- Torque wrench
- Tape measure or a ruler in mm
- A friend to sit on the bike, or a way to compress the suspension
Compress the suspension through its travel while watching the chain. Stop where slack is at its minimum. That is the point you set from.
Halfway between the sprockets, push the chain up and let it fall. The difference is your slack.
Target slack: [00] to [00] mm at the tightest pointAdjusters are a matched pair. Uneven adjusters mean a crooked wheel, which wears the sprocket on one side and pulls the bike under braking.
Use the marks on the swingarm as a rough guide, then sight down the chain from behind. It should run dead straight onto the sprocket.
Full torque on the axle nut, then recheck slack. Tightening the axle can pull the wheel slightly.
Axle torque: [00] NmThe 30 second wear check
Two checks, no tools, done in the time it takes to put your gloves on.
The pull test
At the back of the rear sprocket, grab a chain link and pull it straight away from the teeth. A healthy chain barely moves. A worn one lifts far enough that you can see light between the link and the tooth. Once you can see a tooth face, the chain is finished.
The tooth shape
Look at the sprocket teeth from the side. New teeth are symmetrical. Worn ones curl over into a hook or a shark fin shape, always leaning the same direction. Hooked teeth mean the sprocket goes with the chain.
Rotate the wheel slowly and watch the slack. If it goes from correct to tight and back within one rotation, the chain has worn unevenly. No adjustment fixes that. Replace it.
Cleaning and lube
Grit is what actually wears a chain. It gets between the pin and the bushing, and every rotation grinds a little more away. Lube on top of grit holds the grit in place, which is worse than a dry clean chain.
- Brush the chain dry first, then clean, then dry it, then lube.
- Lube the inside run of the chain so it works outward with rotation.
- Let lube set before riding. Wipe off the excess, since excess only collects dirt.
- Clean after any wet or sandy ride, not on a schedule.
- Do not pressure wash the chain. It drives water and grit into the rollers.
- Do not use heavy sticky lube in dust. It turns into paste.
- Do not let lube reach the rotor or the tire. See the brake guide for how that ends.
- Do not run the motor to spin the wheel while your hands are near the chain.
When to replace
| What you see | Verdict | What to do |
|---|---|---|
| Slack correct, no tight spots, teeth symmetrical | Healthy | Clean, lube, ride. |
| Needs adjusting more often than it used to | Stretching | Start watching it. Order a chain before it strands you. |
| Link lifts off the sprocket tooth | Done | Chain and sprockets together. Both, always. |
| Tight spot in one rotation | Done | Replace. Uneven wear is not adjustable. |
| Hooked or pointed teeth | Sprocket done | New sprocket and new chain, or the new one wears in days. |
| Stiff link that will not free up | Done | Replace. A stiff link skips under load and can throw the chain. |
Parts in this guide
420 Heavy Duty Chain, 120 Link with Master
