Chain jumps on rear derailler
 

When I pedal hard uphill, my chain jumps back and forth between rings when I am on the smaller rings. Chain is relatively new and not loose.

Any ideas what to adjust and how?

Thanks.

are we supposed to guess what kind of bike this is, how many gears it has using what derailleurs and crankset? is it a double or triple? indexed or friction shifting?

when you say rings, do you mean the front chain rings on the crankset, or the rear cogs on the freewheel or cassette? if you have a triple ring crankset, you really should only use the smallest front chain ring ('granny gear') with the larger half of the rear cassette or freewheel. the middle front gear can be used with the whole rear cassette/freewheel, and the big front ring should not be used with the biggest rear gear.

if the chain is skipping on that front small ring when you're in the lower (larger) rear gears, is it actually jumping between the small and middle ring, or just skipping teeth on the small ring? is it rubbing against the front derailleur?

Just because the chain's [somewhat] new, doesn't mean the gears aren't worn.

Quick google turned this up- http://www.cyclingtips.com.au/2009/0...or-chain-wear/ (I skimmed it, sorry if it turns out to be junk)