I am currently running a 10-speed Tiagra compact double 50/34, 12-30 CS-4600 with an unknown type derailleur (labeled "KH", "RD-4601", "JAPAN VIA" ). I am happy with the 12-30 ratio, but would not mind a 32 or 34.
The problem is:
- 10-speed 12-30 is not available anymore, only 11-32 and 11-34.
- The derailleur might not take 11-32 if it is a short cage.
- I don't know which derailleur I have. It is labeled "RD-4601" (no -SS or -GS). The bike catalog says "short cage", but it doesn't look like a short cage to me. The distance between the cogs is about 85mm. It doesn't look like either one in the exploded view in the manual either (the tab to hold the chain near the upper cog is either at 45deg for the -SS or horizontal for the -GS model, but mine is nearly vertical: http://byka.info/system/files/documents/components/Derailleurs/EV-RD-4601-3424A.pdf
What is a good upgrade strategy? I don't want to buy the Ultegra 10 speed cassette, which is expensive and probably won't last as long.
I looked at the 11-32T CS-HG500-10 (4700), but I am not sure it would work with my derailleur. Some posts say it does, but officially it only supports a 30T low sprocket.
Unfortunately the 4600 medium cage derailleur is hard to find and I don't think the 4700 derailleur is compatible with my shifters (different pull ratio).
Would the 105 RD-5701-GS derailleur be compatible with my shifters?