I have a Cannondale Women's Adventure 1 that I got this spring and have been riding on local (paved) trails every weekend. I started off riding about 6 miles a weekend and recently have progressed to 20-25 miles in a day.
About halfway through a ride, my front derailleur seems to need adjusting, I have to wiggle the shift knob to get the chain to change gears. For example, if I'm in 1 and go to 2, I have to pull the knob slightly ahead of 2 (between 2 and 3) to get it to change. To go from 2 to 1, I have to adjust the back gears a few times, or sometimes backpedalling will get it to change (but that's hard to do on a hill).
I keep taking it to my LBS (where I bought the bike) and they adjust it so it works fine in their parking lot, but again after riding for a few miles it's messed up again.
I don't know if I'm doing something wrong in technique or if there's something wrong with some piece of the bike, nor do I know enough about what's wrong to find anything that's helpful. It can be adjusted to shift correctly, but that adjustment doesn't stay for very long. What should I be looking for? Or, could I be somehow doing something when riding to cause this problem?
Some specs on my bike that might be relevant:
Shifters Shimano Revo Twist Type
Cog Set Sunrace CSM66, 11-32, 8-speed
Chain KMC 8-speed
Front Derailleur Shimano M191
Rear Derailleur Shimano Alivio