REAR DERAILLEURS

[Ron Keating]

What (if there is any) is the difference between 9, 10, 11 speed rear derailleurs?

[Joe_W]

The mechanical advantage is (often) different, that is how much the derailleur moves per cable pulled. There is also a difference between brands and (nowadays) mountain versus road. Until 9 speed shimano road and mountain could be combined (and were, especially for bike touring, road bars + shifters with a 3x road crank set and a wide range mtb cassette). General rule: you cannot mix brands (shifters + derailleurs), but there are ways around that (shimergo, cable routing on the RD) as well. At least for SRAM you can mix mtb up to 9spd with road up to 10spd (and below). Shimano:up to 9spd, not sure if 10spd road and 9spd mtb would work. 11spd is incompatible with everything else.

[Ron Keating]

I should have asked a more specific question. i understand that one can't mix and match .
I have recently replaced a 105 9 speed shifter/ cassette with an Ultegra 10 speed shifter/cassette on a road bike.
Didn't change the rear derailleur. I'm having trouble dialing in the indexing over the whole range on the new set up and was wondering if a 10 speed derailleur is needed. Is there a significant difference in the mechanics between the 9 & 10? How the pivot points are spaced or the spring action ?

[Joe_W]

I cannot find the website I used when I put together my tourer... Anyway... I think I recall that incompatibilities started with 10 speed for shimano. I was almost sure that 10 speed road was still using the same ratio in the derailleur...

Efit: I found two of the websites again, I think
https://bike.bikegremlin.com/1278/bicycle-rear-derailleur-compatibility/

https://www.cyclinguk.org/cyclists-library/components/transmission-gears/derailleur-gears/shimergo

Edit 2: did you replace cables and housing? Did you clean up the cut ends of the housing? Makes a difference. 9spd was a bit less finicky.

[Ron Keating]

Thanks for the link to the sites. Should be OK with the rear derailleur as is according to them.
I replaced cables and housings per edit 2 (new 10 sp chain as well). I think I just need to finesse it a little more. It is touchier than the 9 speed.

[Joe_W]

Good luck!