Ah - fair point, if it's a rapid-rise rear mech, i.e. low-normal so that with no cable tension it sits extended with the chain on the largest sprocket, the cable mounting is correct; increasing cable tension will pull the derailleur over toward the smaller sprockets. There's nothing wrong with these derailleurs and, as Anthony says, there's no reason to change it, but it's worth tinkering with it to make sure all four adjustments are correct:
- high-limit screw: stops the derailleur shifting beyond the smallest sprocket and into the gap between cassette and frame.
- low-limit screw: stops the derailleur shifting beyond the largest sprocket and into the spokes - v important!
- B-screw: adjusts the tension on the spring holding the top jockey wheel away from the sprockets - if this is too low, the wheel will sit too close to the sprockets and "chatter", especially in the lower gears (bigger sprockets); if it's too high, it will pull the wheel too far away from the sprockets and shifting will become vague as there's too much gap between the jockey wheel and the gear it's meant to be engaging.
- barrel adjuster: this adjusts the indexing so that the top jockey wheels sits exactly below the sprocket required. If it's too far one way, the chain will rub against the next-biggest sprocket and occasionally 'ghost-shift' down a gear; if too far the other, the chain may not make much extra noise but will occasionally 'ghost-shift' up a gear onto the next-smaller sprocket, especially under load. This can feel a lot like the chain is slipping, but actually it's very rare for a chain to literally slip over the sprocket teeth unless it's very worn or you're putting a lot of force across a tiny sprocket.
It can't harm to give the chain a bit of oil, but be wary of over-oiling it if you use a wet lube, make sure you wipe the excess off with a rag: too much oil sitting on the chain's surface can pick up dirt and grit and end up leaving the chain coated with a nasty grubby oily clag that, in the worst cases, can accelerate chain wear as it's basically covered in a clay-like grinding paste!
Pierre thanks for the tips.
Ill spend some time on it on the morrow and see what happens.
I've never had this problem with any other bike hence I assumed its the rear mech.
My three bikes (in my sig) have normal rear mechs and shift beautifully.
This 'rapid ride' mech is something new as are the shifters hence I was automatically concerned about them rather than the freehub.