Why Does My Mountain Bike Chain Keep Coming Off

The chain of a mountain bike is what transfers the power from the pedals to the wheels. It is essential for a mountain bike to work properly. A chain that comes off frequently can be a sign of several problems, and it will need to be repaired or replaced.

A common cause of this problem is that the derailleur, which moves the chain from one gear to another, has either been adjusted incorrectly or damaged. The derailleur might have been adjusted too high so that it doesn’t reach all the gears on your cassette, or it could have been bent so that it’s not aligned correctly with the gears on your cassette. Another possible cause is that your chain has worn out and needs replacing.

Why would a bike chain keep falling off?

When a chain drop happens, or when your bike chain keeps falling off, usually it’s a problem with the drivetrain system, including the drivetrain bolts, jockey wheel, or the limit screws on the rear derailleurs. There could also be a problem with the chain tension, which naturally decreases as you ride your bike.^[1]

Why does my chain come off when I pedal hard?

If the crankset is loose, it can move sideways during pedaling, which can allow the chain to come off. So make sure the crankarms are securely attached and that there’s no side-to-side play in the crankarm or bottom bracket. Some bottom brackets can be tightened.^[2]

How tight should bike chain?

It should be tight enough that it only allows you to move it up and down about one inch. If it is sagging or much looser than that, you need to tighten that chain up.^[3]

Why is my bike chain popping?

If it is popping OFF, theres a multitude of things that could be causing it, but the most common is a bent cog spike (the little teeth on the gear.) The latter can be a LITTLE expensive, but much cheaper than buying a new bike. Either way, one should always practice proper chain maintenance.^[4]

What happens if chain is too loose?

Too tight, and the tension will restrict your power and force, effectively hindering your motion (and safety). Too loose, though, and you risk a chain jumping off a sprocket; a slapping chain has the potential to damage moto-parts (and rider-parts).^[5]

Is my MTB chain too loose?

To find out whether your chain is too long take a look at it from the side with your eyes being level with the chain. A loose chain will sag close to or below the chainstays as the chain hangs between the rear cogs and chainring. The chain might skip as you pedal, or even drop off the gears.^[6]

Why does my chain go slack when I stop pedaling?

If your chain is getting slack on top when you stop pedalling or backpedal, then the problem is in your freehub (or freewheel, whichever you have), a dirty freehub will cause all the problems you’ve listed, even on a brand new bike.^[7]

How tight should a bike chain be single speed?

Chain Tension There should be approximately one half inch of movement in the chain up and down at a point half way between the front and rear sprockets. To change the tension loosen one of the axle-nuts and move the wheel forward or backward slightly and snug it up again.^[8]

What lube should I use on my bike chain?

Use a light, waterproof lube such as Boeshield T-9 Waterproof Lubricant. For wet-weather conditions, try Pedro’s Chainj. Never Use: Motor oil—it contains acids and particles of metal that can compromise a chain’s strength and cause it to wear more quickly.^[9]

Why does my chain slip under pressure?

Gear indexing issues One of the most common reasons for a skipping chain is simply a drivetrain that needs a simple indexing adjustment. This is so common that even many brand new bikes can exhibit these symptoms. The good news is that this is probably the simplest to diagnose and fix of all potential issues.^[10]

How many miles should a chain last?

Replacing your chain regularly can prolong the life of your drivetrain. Most mechanics agree that you should replace your chain about every 2,000 to 3,000 miles, depending on your riding style.^[11]

How do I know what size mountain bike chain I need?

Simply find out how many gears, or ‘speeds’, you bike has (count the number of gears on the rear cassette and multiply it by the number of chainrings at the front), and pick the corresponding chain.^[12]