Weird Chain Slip
 

Whats up guys, so i've had my Trek 2.1 for about three weeks now and am loving it so far. I noticed today though that when i'm in the lowest gear on my cassette and i pedal backwards the chain slips off and jumps a gear or two down but not on the teeth of the cassette. I don't get any slip at all while pedaling forward just when i pedal backward. I noticed at a light today i pedaled backwards to get my pedal in my normal starting position and when i started to pedal i felt the chain slip but really it was jumping back to the lowest gear, which is the gear i had it in when approaching the light.

When i got home i had my dad hold the rear tire in the air and i tried out shifting through every gear starting with the lowest gear then to the highest and back to the lowest and it shifts perfectly. I pedaled backwards on all of them and no chain slip, just slips when its on the lowest gear. Anyone know why this is happening, i'm gonna take it the shop i got it at to see whats up, i just thought i'd ask here too to get any ideas of what it could be. Thanks a lot.

Are you on the big or small ring in the front? If on the big it might just be too much angle on the chain for it to roll smoothly backwards.

If it works fine pedaling forwards then don't worry about it.

I'm on the big ring up front. Hmm, didn't even think about that, thats probably the problem then.

You'll find a lot of opinions on 'cross chaining' or using the little ring in front and the smallest cog in back / big ring in front big cog in back. Most people seem to agree that it can cause excessive wear on your drivetrain and should be avoided, other disagree and say use all the gears you want. I'm of the opinion that if you find yourself in that gear on a hill stick with it, but avoid it otherwise. Try the same thing in your big ring / second to largest cog.. my guess is it won't happen. Since the bike is new however, it wouldn't hurt to have the shop look at it.

It could be cross chaining like mentioned above or your B/limit screws are not adjusted properly. But you should avoid cross chaining.