This is my first post. This sight looks awesome!

I have a 21 speed with shimano gears. Recently my chain started jumping or skipping when I ride, especially under high tension (standing up etc.) I adjusted the front and rear derailers, but it still does this. Could the chain need shortening? Any suggestions as to where I should take a look next?

Thanks,
Bill

It could be that your chain isnt compatible with your drive train....it could be that you need a new chain ( chains should be replaced once every year or two at least)...it could be that your rear derailer needs its limits adjusted...or it could be that you are riding in a gear ratio that stretches your chain too much.

Thanks for the advice.

Anyone else have an idea? Would a new chain be in order?

Thanks,
Bill

I'd start with a new chain, but some of the rear cogs may be worn. If it only skips on one or two that is a good indication that they are worn. But a new chain would be in order anyway.

Thanks! I'll start there.

I appreciate all of the good advice.

Welcome to BikeForums!

Sometimes, "auto-shifting" can be caused by frame flex, which also occurs predominantly under hard efforts. But that's not a problem that would have just manifested itself, unless your frame has cracked or been damaged. It's worth a check just to be safe.

You can check the chain by measuring. On a new chain, you should be able to measure exactly 12" from center to center of 12 inner/outer link pairs. On a worn chain, if it measures 12 1/16", it's time to change it. If it measures 12 1/8", you're overdue and wearing out your drive train.

A lot of people complain about gear wear on the freewheel. I notice it more on the chainrings (maybe it's a roadie thing). Either way, if that's the problem, the new chain will make it worse (since they've worn adapting to the "stretched" chain).

I'm fairly convinced that your cogs are toast, and that they will need to be replaced. Also, the chain must be replaced at the same time.
Cogsets are about $40 each, and a decent chain will set you back about $25.

And as a last resort, you could always measure it to see if it is worn past specs.

Cheers...Gary

Thanks for all of the advice. I appreciate all of the help. It is the cogs and I will replace the chain along with the new cogs.

Bill

Bill, where in michigan are u at?

If you determine you need a new chain, you may have to replace the freewheel and chainrings as well. Usually a new chain won't jive with the old components.

If you replace the chain and the freewheel, sometimes you can turn the chainrings around and use the teeth from the other side.

Good Riding!