Unwanted shifting

[runcommute]

I've been riding a 2002 IronHorse to work and stuff, and it recently just started shifting gears when I didn't tell it to. It does it now quite frequently. Is the cable probably just loose, or could it be my dirty chain and cogs? How can I adjust the cable tension on a bike like this?

 

[gclark8]

Give it a birthday, have the bike shop fit some new cables.

 

[kdelong]

Is it shifting or is the chain skipping? They can feel the same if you don't have any experience with chain skip. If the chain is skipping, you need to replace the chain and/or cassette. If you don't know how to adjust the cable tension on your bike, I suggest that you take it to your LBS and let them look at it.