Hi. My wife's just bought a M Bike with the normal triple set-up. The shifting up from small-middle-big is fine, but no matter how much I tighten or loosen the cable, either by unclamping it or via the adjusters, I can't get it to shify from the big back to the middle (it just moves enough for the chain to rub - no where near enough to shift it). However, if I then shift to the small ring from there, no problem. Any advice appreciated.