Shifter / derailleur comparability

boileroo

Just a quick question regarding the compatibility of shifters with derailleurs. Im currently looking at changing my cassette to an mtb one to help me out on the hills around here (just moved from Norwich to bath, my weedy legs can't manage yet!).

To put the mtb cassette on I'll have to change the rear mech as well to accommodate the larger cog. What do I need to be aware of regarding compatibility between the derailleur and the shifters? I currently have shimano 2300 8 speed shifters on the bike, so will any shimano 8 speed derailleur be compatible, mtb or road? If not, what are they key points to look out for that dictate whether or not any given rear mech will work on my bike?

Cheers!

mateotu

Any Shimano 8-speed rear derailleur will work, but the better-quality Shimano stuff is not available in 8-speed any more so you may be stuck with Alivio if you go this route. If you want something good, go for a Shimano 9-speed Deore or SLX or similar - 8-speed chain is slightly wider than 9-speed but it still works perfectly. Just avoid anything 'low-normal'. SRAM rear derailleurs are also nice, but most of them use a 1:1 actuation ratio which won't match your shifters. General point: make sure the total capacity of the derailleur is enough to handle your front chainrings - long cage is best if you're running a triple.

nicklouse

you can use any road or MTB shimano rear mech as long as it is not a MTB 10spd as they have a different pull ratio.

drlodge

nicklouse wrote:

you can use any road or MTB shimano rear mech as long as it is not a MTB 10spd as they have a different pull ratio.

+1 wot da man said.

I'm using those same 2300 8 speed brifters on my 7 speed cassette with a 10 speed Dura Ace RD. As long as the pull ratio of the RD is the same, it'll work fine.

boileroo

Thanks very much for all the help guys, really useful explanation.

So (sorry to repeat but just making sure!) I can use any shimano mtb or road rear mech, even a 9 speed, as long as its not an mtb 10spd. Sounds good to me! I'm currently using a 50-34 compact and hope to use a 11-32 cassette. That would mean needing a mech capacity of 37 right, which would be long mtb?

Thanks again for the help

nicklouse

Basically yes. BUT two things to look out for.

The mech can manage the biggest cog on your cassette. Some road ones can manage the same as MTB and lastly the range of the mech. Can it over the tooth difference. Dies it have the capacity? All to do with cage length.

mateotu

Yup, you need a capacity of 37, so that means for Shimano MTB you need long cage.

andy_wrx

Like Nick says, any non-10sp MTB Shimano rear mech which has the tooth capacity will work - it doesn't have to be 8sp

Basically the shifters need to match the cassette, but not the derailleurs.
The rear mech doesn't 'know' whether you are running 10sp or 9sp or 8sp - the shifter pulls/releases the correct amount of cable per click to make the derailleur to move sideways the distance needed between the cogs on the cassette
10sp cogs are closer together than 9sp, 9sp closer than 8sp; a 10sp shifter pulls/releases the matching smaller amount of cable per click than a 9sp shifter does, and the 9sp the matching smaller amount of cable than a 8sp shifter
The mech just moves sideways the distance that this amount of cable pulled/released tells it to.

10sp MTB hower changes this - the mech moves a different distance sideways for an amount of cable.
And Campag and SRAM are different too.

But you'll be OK with any Shimano 8sp, 9sp or 10sp road derailleur, so long as it has the capacity you need