Shifter/brake-lever compatibility with front and rear derailleurs

Question

I am currently converting my bike from flat bars to drop bars for a long touring cycle. I used to have Shimano SL310 shifters (8x3), but have now bought Shimano Sora ST-3300 (8x3) to mount on the drop bars.

I understand that such levers have a shorter "pull" than my previous ones and therefore require different components elsewhere. This is easy enough with the brakes, I've bought cantilever rather than caliper brakes, however, I'm finding the derailleur situation more complex.

The Shimano archives suggest pairing the levers with a RD-3300-SS (http://si.shimano.com/pdfs/si/SI-5TT0A-000-00-ENG.pdf), but with a drivetrain capacity of 35 and max cassette size of 32T I think I would need the longer cage version RD-3300-GS. This is quite old and hard to find, I would rather simply buy a new one. Does anyone have any suggestions as to newer models of rear derailleur that may work?

Would a newer Sora model (which all seem to be 9 speed) work? I'm worried about the cable pull ratio.

I am yet to delve into the front derailleur issue but I assume it will be along the same lines.

Answer 1

You can actually use any 8, 9 or 10 speed Shimano rear road derailleur, or an 8 or 9 speed rear mountain derailleur with your 8 speed shifters and cassette.

The reason for this is that Shimano used the same actuation ratio (ratio of lateral movement to length cable pulled) for all those derailleurs. As long as the shifters match the cassette it will work.

There is one exception I know of which is Tiagra 4700 10 speed, which uses Shimano's 11 speed actuation ratio (See Compatibility of bar end Shifters and 10 spd Tiagra).