Chain skipping to higher gear on trainer

New bike, right?

Your cable has stretched, take it to the LBS and have them adjust the shifters for you. Ask to watch as they do so you know how to do touchups with it.

(edit) Oops, I missed the mileage.


3000 miles, get one of these:
http://www.parktool.com/product/chain-checker-cc-2
Most bike shops carry it.
Measure your chain. At about .75 buy a new chain. The next time you go to clean your chain, just break it and put the new one on.

I'm guessing you need a new chain at least. May have worn out the cassette just enough to screw with shifting.

Edited by DanielG 2013-04-20 3:41 AM

Put it in that gear and spin the crank by hand while watching the rear derailleur in that gear.  You will probably see that it is lined up slightly off.  It is likely that cable is ever so slightly too tight.   You can confirm this by seeing how it lines up on that cog.  You can make very, very incremental adjustments to the cable at the rear derailleur using a barrel adjuster if there is on or where the cable connects to get it perfect.   Also, you should get out a ruler and measure your chain.  If you measure from pin to pin it should be exactly 12".   If it is a few mm longer you probably should replace it.  How worn are the cogs on the rear cassette?

It could be that you're compressing the axle a bit with the trainer, which moves the derailleur inwards, causing the skip on the trainer, but never on the road.

Losen up the compression a bit and you should be fine

Edited by audiojan 2013-04-20 2:55 PM

Most likely cable stretch. Your chain doesn't have near enough miles on it to stretch yet. Adjust the barrel adjuster on your rear derailleur, or take it in to the LBS and have them do it if you don't know how. They shouldn't charge you for it if you bought from them.