Bicycle Mechanics - Gears Switching...

Folks,

Im quite new to the road bike scene and am therefore easily frightened about messing up the bike. I've got a Trek 1400 with ultegra components and as of recently i've noticed that when im riding along...my gears will occasionally switch on me. I hadnt noticed the problem until I got a rear flat and fixed it. Perhaps I put it back on incorrectly and its now messing with the deraileur. Regardless, what's the experts diagnosis based on what I have given you thus far. Any words are appreciated.

Hi Cutter

There are a couple of things that might cause your gear problem that spring to mind immediately:
1, you mention that you removed the rear wheel to fix a flat - is the wheel replaced properly? sometimes with my bikes it is possible to get the rear wheel slightly mis-aligned.

2 If the bike is new, the gear cables can take some time to settle in, so the alignment on index gear systems will drift. Once you are sure the wheel is mounted properly, check the alignment of the rear derailleur jockey wheels with the sprocket of the gear selected, the chain should run straight from the derailleur to the sprocket (when viewed from above), not deviating to the left or right as if it were about to shift. To fix a mis-alignment the barrel adjuster is used, a notch at a time until the derailleur and sprocket are in-line. Be sure that you are adjusting to the correct sproket that the index system "thinks" it is in, or the system will be out of sync. It is also a good idea to check the high and low limit settings on the rear derailleur and make sure the top/bottom gears can be selected and there is no danger of the chain coming off.

If you are not sure about any of this, your LBS ought to check this for free, as the bike is new.

Hope this is some help,

Ed

I'm going with Ed's Number 1. Check the alignment of the rear wheel.

Thanks folks-

I'lll try readjusting the wheel and using the barrel adjusters if that doenst work. If all else fails, to the LBS I go.

Many thanks