Bicycle Mechanics - 9-speed RD the same as 10-speed RD?

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creativepart
05-10-11, 10:40 PM
I may need to replace my 5 year old Shimano 105 RD. I have a 9-speed cassette and brifter. I sort of remember hearing that I could just use a new 10-speed 105 RD to replace the older RD. Is this true? Or do I need to find a 9-speed RD to replace my current 9-speed RD???

I'm not trying to change to 10-speed. I'd use the new RD on my 9-speed cassette with my 9-speed brifter.

JiveTurkey
05-10-11, 11:44 PM
Yep, totally compatible. Both RDs have the same cable-pull ratio. The shifter will tell it where to stop for each gear, regardless of how many gears there are.
relyt
05-11-11, 12:50 AM
They have the same cable-pull, however a 10-speed derailleur is likely to have narrower pulleys for the narrower 10-speed chain. But that doesn't matter in this case because a 9-speed chain will still work.

Boye
05-11-11, 07:15 AM
It will surely work. Here the 105 5700 RD is sold as being 8, 9 and 10-speed compatible: http://www.ribblecycles.co.uk/sp/road-track-bike/Gears-Rear-Road-Shimano-105-Silver-5700-10-Spd-Rear-Gear/SHIMGRRR520