Why does bike chain fall off

On a perfect chainline, a straightedge will exactly bisect the cassette. If the straightedge is off by more than a cog in either direction, you can decide whether or not to look into solutions based on your shifting performance and any chain drop issues.

Why do you dismiss checking the front derailleur alignment? This was my problem and has been fixed. Operator error also, failing to trim when on big ring and near large cog lets the FD take a full swing at an enhanced angle can cause the chain to off.

Sorry for the confusion, Frank. I wrote that I was providing tips based on the assumption that the front derailleur is properly adjusted. I was focusing on things that are less obvious and need to be figured out. Hope that explains better. Oops, that was an oversight on my part, Gregory. I meant to explain that in the story. On each straightedge position you note where the straightedge rests on the cassette and find the middle point. That middle point should be on the middle point of the cassette with a perfect chainline.

Thanks for letting me know I forgot to explain that. Largest chain flexes under load, causing chain to skip or fall off. Both sides ie when pedaling on left side, chain ring flexes left. Same with right. There does not seem to be any play in bottom bracket bearings. Just go around and put a wrench in every bolt and see if any are loose. They should all be quite tight.

Hope that fixes it for you, Jim. Great article. Thank you. My chain often fell off after I stopped the bike, after any backward movement of the pedals. In my experience, this can happen even if the drivetrain is set up perfectly with new parts. Now, to prevent parking lot drops, I shift the cassette to a middle gear, before stopping the bike. I weigh lbs. The frame twists enough to cause the chainring to be misaligned with the chain if I put too much force on the pedals.

This is one of the reasons that custom framebuilders go to oversize designs to stiffen the frame and reduce the flex, Rich.

I have experienced this and after investigating all of the aforementioned possibilities finally zeroed in on the rear derailleur pulley spring being worn out.

Thanks for explaining how it caused the chain drop, too. On big bumps my chain sometimes drops to the small chainring. Is this indicative of a too long chain? Jim, another reason for the rear derailleur pulley misalignment is the derailleur hanger being loose. I had this problem on a mtn. While shifting the gears, these derailleurs help for moving the chain. In this way, the bicycle chain shifts its place onto the chosen gear.

This is the basic working process of a bicycle chain. Due to several reasons, the bike chain can fall down. Such as loose chain, inaccurate front or lower derailleur, too long chain, worn-out chain components, etc. At this point, you will need a chain tool to fix the chain.

Also, it is possible to fix the bike chain only with a hammer and pliers. But, the chain tool makes things easier while on the street. If your electric bike chain started falling off frequently, that means some setup may change. So, the first thing you have to do is make sure the drivetrain bolts are tight.

Also, inspect that everything is in the place and not get whacked or the rear wheel is correctly positioned. Hang the bike from a stand or turn it back upside down. It will make the fixing process easier and keep the bike steady while working on it. The bike should rest on its seat and handlebars. Look out for the gear the bike is on and where the chain is resting now. Another way to keep the chain from coming off the inside of the chainset is to use a chain catcher.

A chain catcher is essentially an arm that acts as a barrier to the chain overshifting inwards. If the chain is coming off the inside of the cassette, put the chain onto the smaller chainring at the front and the largest sprocket at the rear.

Then turn the L screw clockwise until you see the rear derailleur cage the section that hangs down start to move away from the centre of the bike. You need to move it to the point where the chain can move freely into the largest sprocket, but can go no further than that. If your chain is coming off the outside of the cassette, put the chain onto the larger chainring and the smallest rear sprocket. Then turn the H screw clockwise until you see the rear derailleur cage start to move towards the centre of the bike.

You need to move it to the point where the chain can move freely into the smallest sprocket, but can go no further than that. In most cases, the rear derailleur pulleys should be lined up directly underneath one another. If you do all this and your chain is still coming off, there are several other things to look at:. Check that it is positioned correctly by taking a look at our article on how to index front gears.

Shifting performance can start to become less smooth and more erratic as components near the end of their useful lives. Again, a visual check will tell you what you need to know. Pull the two ends together and add one complete link one inner and one outer half link to get the correct chain length.

There are other reasons why your chain could come off, but we think these are the main ones. If you like road. Forgetting about adjusting this screw is a strong reason for the chain to fall and get stuck between the cassette and the frame.

This part is made up of aluminium designed to break during a crack or hard hit to prevent the frame from damage. This is mostly applied to carbon frames which are very fragile. In order for the derailleur to do its job it has to be in perfect vertical alignment cassette cogs. With a certain degree of bend when the derailleur shifts to the lower of the largest cogs it can make the chain falling and stuck. Bad quality shifters can lose cable tension while riding causing the derailleur to shift undesirably.

If you want to test your shifter cable tension resistance, you can pull the cable quite hardly and look at any loss in tension. This applied to mountain biking discipline which is known for hard riding terrains with a lot for bums and jumps.