My brother recently bought an older bike that needed a lot of work. I replaced the brakes, chain, brake cables, and then the rear derailleur, with more to do.
The bike came with a 10sp 12-28 cassette with a Tiagra short-cage RD. It was only AFTER I sized the new chain that he bought medium-cage Tiagra RD (RD-4700-GS), so it’s probably a link or two short.
The bike is shifting poorly in the middle of the cassette. When shifting up, it will get through the first few cogs fine, then struggle to reach the larger cogs unless I add tension to the cable. However, if I leave this tension on, then it won’t shift back down the cassette.
The limit and B-screws are set properly. I do not think the hanger is bent.
I still need to replace the old shifter cables. I thought they might be frayed, but this bike did not see a lot of use from the original owner.
What’s the most likely cause? Short chain? Old shifter cables? Shifter indexing issue?
I’m only after dealing with a shifting issue on a 4700 group myself, could only use 9 cogs missing either the top or bottom gear depending on tension. Changing the cables fixed this for me and it’s working crisply now - when I removed them from the housing I could see my RD cable was starting to fray and was damaged on the shifter end also. Might be worth even checking the condition of the cable that’s currently installed if possible. Hopefully it’s a similar fix for you also.
Then hanger alignment, this doesn’t need to be mm perfect for 10sp but it need to be something like square.
Could also how the cable is clamped at the derailleur. On there derailleurs is it easy to see where the cable goes as I’m sure there is a white indication mark but if not, remove the cable clamp bolt and there will be an indent where the cable needs to go into.
A worn chain and/or cassette can also be the cause of poor shifting, have you checked those for wear.
Lastly, are you using 4700 shifers and not the older shimano 10sp road shifters (105 5700 or Ultergra 6700)? The cable pull on those older shifters will not work with 4700 Tiagra 10sp because that has the same cable pull as 11sp.
Looks like that’s your issue - 4700 (and GRX400) changed to the 11 speed pull ratio so isn’t compatible with older 10 speed. You’ll either need to change shifters to 4700 or find another old 10 speed derailleur to match the shifters.
Edit: just noticed that Alex noted this in his reply above already.
Man, I would never have figured that out. I’m thinking it makes more sense to upgrade the shifters to 4700 than downgrade the RD. The 4700 shifters at least don’t have that awful side cable exit.
the 4700 is an orphan in Shimano’s 10 spd range - it’s the only one that doesn’t play nice with the other 10 spd models.
front derailleurs don’t matter as much. as they only shift between two positions (neglecting the trim on some shifters) you can get them to shift OK even when the pull ratios are not strictly compatible.
The 10sp incompatibility has caught out a few of my customers before who have replaced a broken 10sp derailleur with a Tiagra 4700 one and cannot understand why shifting is wonky.
Another option is to use a 11sp road shifter. They have the same index/pull ration as Tiagra 4700
