My bike gears change constantly and on their own?

It's the back gear that keeps switching and the front gear is always on the lowest wheel (out of two). I would love to know how to set the back gear.

Somebody told me that it was derailed and it would be amazing if someone could just tell me where or how to fix it that would be awesome (or, if you can't do that, just how to make it freeze on a certain gear and not move at all).My bike gears change constantly and on their own?
the cables are either bad, or not tight enough. You can try and adjust them on your own, or take it to a bike shop for 60 bucks or so. IF they need to be replaced, I recommend having a pro do it. I can do it, but I hate to. I would rather be riding.



here is videos on how to adjust front and back derailleurs.

http://www.youtube.com/watch?v=ngm6dr-1n

http://www.youtube.com/watch?v=2j1gSwhsVMy bike gears change constantly and on their own?
your drivetrain needs adjusting.



Probably you got the bike new and the cables are stretched.



You can go to the LBS where you bought it - if they sell a new bike, usually a first tune-up is included for free. If not, I would take my business elsewhere, a tune-up does not cost the world.



If you bought a department store bike because you are cheap, tough luck. Try to get them to do the adjustment and otherwise, tough luck again.

If you bought a department store bike because you seriously did not have the money, be consoled: Sheldon Brown teaches all about adjusting a drivetrain:

http://sheldonbrown.com/derailer-adjustm
http://bicycletutor.com/part/rear-derail