My road bike (sorry!) loses indexing after about 50km or so. It is perfect to start off with but always ends up needing tweaking an hour and a half or so into the ride.
The cables are new about 2 months ago, everything is tight etc.
Any ideas? (methinks it might be time for a new rear mech.)
cheers Jon
Are the barrel adjusters moving?
Something must be loose. If the indexing is OK at one point in time then the mech is fine.
stretch the cable by putting the bike in bottom gear and pulling it hard between two frame-stops. (what this achieves is actually compressing outers & stops) & re-set.
Check clamp bolt on rear mech is tight & cable outer under bar-tape is tight against lever.
It's trying to tell you something.
Possibly single speed related 🙂
Inline cable adjusters? They are renowned for rattling loose.