Bicycle Tutor

I have a 2003 giant OCR frameset and I built it up with Sora groupset... so far so good, has made a nice budget racer. But I wanted to up grade to standard chainrings, 53/39, so i bought a Truvativ elita chainset. Fitted it no problem... but,when on small ring and i go to use any of the bottom 3 sprockets at the rear the chain changes to big ring at front without touching front mech! The chain line seems very extreme, any solutions out there?

The chances are that the chain is catching the "lift pins/ramps" on the rear of the big ring.
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http://www.sheldonbrown.com/gloss_ra-e.html

The only suggestion I have is to fit a wider bottom bracket to move the chainset out a bit.
(You just might be able to fit a 2mm or 3mm spacer behind the right side of the existing bottom bracket to give a bit extra offset. I have done this on a couple of bikes with Shimano cartridge types.)

Actually you shouldn't run the extreme gear combinations, so it is not that... bad. Check the specs (BB width) of the old and the new derailleur to see if there are differences.

Well apparently the problem lies with the Elita being a 10 speed chainset and i'm running it on a 9 speed system! Ive been informed by the people i bought it off that it will work on 9 speed but may have a problem with the slightly wider chain of the 9 speed. Its a shame they didn't mention that when i first asked them! The bottom bracket cannot be spaced due to it being a sram GXP variety which doesn't except spacers! And I know those bottom 3 gears shouldn't be used, but we all do sometimes.....? Thanks for replies.