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Sounds like a few problems.

Trouble shifting down to smaller chainring could be that the derailleur cable has stretched out, which is expected and normal. They can probably make a quick adjustment to trim this up. Another thing to consider is what gear you are at in the rear. Try to keep the chain parallel to the bike as possible to avoid "cross chaining". Shifting down can also be difficult if you are pushing really hard and the chain is under a high load.

Lastly, the chain coming off completely shouldn't happen under normal circumstances. Your limit screws probably need to be adjusted.

All that said, the bike is new enough that the Trek store should make all of these adjustments for free. Show some interest and they'll probably show you what they are doing so that you can learn about your bike!

Yeah, if you bought it at any of the Trek of Pittsburgh stores, you should be covered. I frequent the Robinson and East Liberty stores all the time. (Even adjustments that aren't covered are CHEAP!)

To be honest, I'm glad this was posted. I'm about to buy my first derailleur-equipped bike since over 10 years ago, and it's good to have a head's up on any potential issues.

@dmtroyer - Yes, I was keeping the chain as parallel as possible. I think when I was just starting out a few weeks ago, I wasn't as diligent with that, but I definitely have been lately. When the chain came off the ring on Saturday, it was after I'd done quite a lot of climbing...what had happened was I hit the trigger to downshift, then it took so long, I wondered if I had actually hit the trigger fully, so I hit it again, and the chain came off.

Earlier today, I was in the biggest ring, and hit the trigger. It just stayed in gear, although I could hear a clicking noise (like the derailleur was trying to shift, but failing.) I hit it a second time and it downshifted all the way to the smallest ring, bypassing the second.

If I have time, I'll take it to Trek tomorrow. Just curious, what are limit screws? Is adjusting them a big project?

Limit screws adjust positioning of the derailleur, they normally don't need to be adjusted if the bike was put together correctly.

Front limit screws

Rear

Leave it to a bike shop:

Front adjustment http://www.parktool.com/blog/repair-help/front-derailleur-adjustments

Rear adjustment http://www.parktool.com/blog/repair-help/rear-derailler-adjustments-derailleur

@jkp1187: I used to have this happen to me on a different model of bike.

What helped was making sure that I was still pedaling while shifting to the smaller front chain ring, but not having too much torque on the pedals. Try shifting a bit sooner than you need to and/or easing up on the pedalling power while you do it.

@Pseudacris - Thanks for the suggestion. I have been trying to be more aware of how much pressure I'm exerting while shifting, although on Saturday when the chain came off the gearring, I was starting to go up a hill.

Would turning the barrel adjuster in the back a little bit be something worth trying?

Plenty of good advice here.

It sounds to me like it needs a good adjustment.

On hills sometimes it helps to switch to the small chain ring before you have to. If you are pushing too hard the chain has a hrad toime moving. If you are caught in the wrong gear, you have to push hard to keep from stopping all togethr.

Might not be your problem. It sounds like adjustment to me.

no, do not adjust the barrel adjuster in the rear. that is to control the alignment of the rear derailleur, and will help fine-tune (or un-tune) your right hand shifter.

not much more to add; all this advice is solid. however, i did want to say that this thread reminds me of the joy i've had since shifting (if you'll pardon the pun) to a friction shifter for the front derailleur. now if it just needs a little extra, i can give it that little extra, instead of hoping it will just magically happen sometime.

"Now if it just needs a little extra, i can give it that little extra, instead of hoping it will just magically happen sometime."

I've actually found that most mtb style shifters just need that "little extra." Only the Shimano fronts are indexed, the Sram operate as frictionshifters from what I understand. Just rotating the shifters a tiny bit for better leverage is another possible way of fixing the problem for the left hand (it has worked for me on Shimano shifters too).

Shouldn't be necessary on a new bike, but FWIW the jump stop is probably the best $10 i ever spent on a bike accessory (er, looks like it's now $12 but still a deal).

Took it out for another ride in the rain last night for a couple of miles. Did all kinds of shifting, didn't have any problems. I noticed that it tends to happen at the end of a long ride, so I might take it for a long ride, see if the shifter starts balking, then take it to Trek.

keep in mind at the end of a long ride you'll be riding differently too. Not sure how much you've been riding for how long, but I know there's a point beyond which I sit differently, push on the pedals differently, and just past that I start to think a lot differently (poorly). At that point I stop trusting the difference between what I'm trying to do and what I'm actually accomplishing. That's a personal hydration/blood sugar issue, but figured I'd throw it out there, as it can also come up. I'm sure Trek will fix you up nicely

That is a fair point.

@jkp1187

When you shift down to the smallest chainring, two things need to happen that take a little bit of time: 1) the chain needs to fall onto the smaller ring; 2) the tension on the spring on the _rear_ derailleur needs to take up the new slack in the chain. It's not a lot of time, but it does take a certain developing of what this feels like.

My triple on my MTB serves me well and shifts fine, but If it's my goal I can very reliably throw my chain by shifting from the biggest ring directly to the smallest while pedaling with power.

@HV

FWIW, The better Shimano front-indexed shifters do have trim adjustment; I.e., you can push a just little bit more to give the chain that extra push.