Sorry for a gearing question but I've searched high and low for an answer and can't fix it. I have an 07 Allez Triple, it came with a Shimano 12-25 cassette. I'm going on a tour so have fitted a SRAM 11-28 cassette and a new shimano chain. I fitted the cassette ok, put the chain on, set the length according to parktool, gear shifting works fine. But whenever ANY load is put on the chain when it's on the small cog (11 tooth), the chain jumps badly on that sprocket. I've tried shortening the chain - no affect Tried changing the high limit screw - no affect (it's perfectly aligned) Tried every b-tension under the sun - still does it at both ends of adjustment and middle. I've also taken the cassette off the wheel twice and put it back on, making sure it's tight - no affect. Can anyone offer any help, I'm off touring in 36 hours, would be very grateful.