I just picked up my new Trek 7.3 FX today. They spent a good amount of time tuning it up and installing my bike computer before they did the final fitting and sent me home. I did ride the bike at the store but didn't get into the 8th gear any.

When I went for a spin around the neighborhood I noticed that whenever I'm in the 8th gear on the back (sorry I'm not familiar with all the bike terminology) that the chain is rubbing in like 3 - 4 different spots on the metal guard/guide. It happens in all 3 of the big gears whenever I'm in the 8th gear in the back and makes quite a bit of noise.

My LBS closed at 7 so I'm just trying to get some info on what could possibly be the problem. I'm sure if I call them tomorrow I can take the bike back in to get the problem fixed, but hopefully you all can ease my mind. I don't want this to be a serious problem since they already installed my bike computer.

Well first off if you are in the largest gear in the back then you should not be in the largest gear in the front and visa versa. That is called cross chaining.

As for the other gears it is probably a simple adjustment. You could try giving your front shifter a little tap when it rubs. That might cure it.

Yup. Certain combinations will cause chain-rubbing on the front derailleur (FD). As well as premature wearing of the chain and cassette. Here is a caution that Shimano puts in with their FD's:

Thanks! I guess I will just ask about it next time I stop at the LBS. The information posted makes me feel better about things.

I haven't had a bike since I was a kid, so I'm still learning about what gears to use and such.

Wow, nice chart except, on the 2nd, 3rd and 4th one, the spelling is all wrong.

Ok, ok, just kill this reply. Deepest, heartfelt apologies.