Bicycle Mechanics - Derailer Question from someone w/o too much fixing knowledge

So, I have a giant OCR 2 w/ tiagra/105 components.

I just started getting back onto my bike after a long absence (knee surgery and broken foot). I'm riding the bike on a cyclops trainer right now.

Here's the problem:

If I am on the smallest chain ring on the front, and about the 3rd biggest on the back, the chain will sometimes slip into another gear then fall back into place. This happens fairly often, and also happens in a couple other gears as well. In addition, if I am on the middle ring on the front, and the 2nd largest on the back it will sometimes slip as well.

The front doesn't seem to slip, only the back. I'm wondering what type of derailer adjustment I should need to do. Thoughts?

Thanks

probably just a minor barrel adjustment.

So, I have a giant OCR 2 w/ tiagra/105 components.

I just started getting back onto my bike after a long absence (knee surgery and broken foot). I'm riding the bike on a cyclops trainer right now.

Here's the problem:

If I am on the smallest chain ring on the front, and about the 3rd biggest on the back, the chain will sometimes slip into another gear then fall back into place. This happens fairly often, and also happens in a couple other gears as well. In addition, if I am on the middle ring on the front, and the 2nd largest on the back it will sometimes slip as well.

The front doesn't seem to slip, only the back. I'm wondering what type of derailer adjustment I should need to do. Thoughts?

Thanks

http://www.parktool.com/repair/readhowto.asp?id=64

Could be as minor as #2 suggests or more than that. Easiest way to do this is start from step #1. A lot of things can cause the symptom you're describing. You'll need to do a bit of legwork to understand the type of adjustment and problems.

As the others said, it could be a barrel/trim adjustment, or could be more complicated, but you might as well start with the simplest and either solve the problem or eliminate it before looking farther.

The last section of housing ends at an adjuster on the RD. If you turn it outward, it lengthens the housing, effectively shortening the gear wire, and moves the RD inboard. Turn it in and the opposite happens.

Leave your bike on the trainer, but lower the resistance unit so the wheel spins freely. Put your bike in any gear and eyeball the chain and cassette from the back. See if it's feeding perfectly centered onto the sprocket. If not turn the adjuster until it's centered then run through the gears. Ideally it should be smooth and quiet in each gear and shift equally well in either direction. If it shifts inward better than outward turn the barrel in a bit, or out if it shifts out better than in. Since you're new at this feel free to experiment, trial and error with 1/4 turn adjustments until you dial it in.

When you're finished, double check that the inner limit is OK by pulling on the bare wire and trying to shift beyond the low gear cog. If the chain goes over the top, tighten the low gear "L" limit screw by 1/4 turns until you cannot make it overshift.

If you can't solve the problem easily this way, it could be a bent hanger, especially if you wrecked your knee and foot crashing this bike.