Hey guys, having an issue with a 9 speed tiagra setup with brifters on a bike I’ve just built. I’ll adjust the cable tension and get the shifting perfect, but after five minutes of riding, shifting up to the lowest gear only gets me five cogs up the cassette. It’s not a gradual decline either, all at once the derailleur will just shift down three gears and stay there.

I’m not sure what the issue is, and it keeps repeating every time I readjust the cable tension in the rear mech. If the cable was coming loose (and I find it hard to believe with how hard I tightened the bolt) then wouldn’t it just shift all the way down to the highest gear instead of fourth/fifth? Apart from that, shifting between the four/five gears I end up having is fine (so the cable isn’t frayed or dead, as the pull ratio ends up the same). Any ideas?