mtb rear derailleur on 'road' bike ?

generalcyclist

I have a 'commuter bike' which is really a road bike with a flatbar

Can I replace the 'road' rear derailleur with a mtb rear derailleur ? Any compatibility issues ?

Also my rear cassette is 8-speed. Does the rear derailleur need to be 8-speed (only) ? There seems far more choice for 9 gear derailleurs

Ouija

8 and 9 speed are cross compatible in most regards (8's sometimes don't work with 9's but nearly all 9's work with 8's). Only thing you really need to know is weather your using SRAM or Shimano compatible rear derailleur. You can't swap from one to another so if it's currently SRAM, replace with SRAM etc.

generalcyclist

thanks. It's shimano shifters, so I'm looking at shimano

Does it have to be 'direct mount' ?

Ouija

Depends what your current system is using? If it's attaching to a traditonal mech hanger then, no.

reformedfatty

I don't know regarding 8 or 9 speed, I would have guessed not as would have thought the cable pull would be different, but can't be certain.

On the other half's bike I recently replaced the road cassette and derailleur (9sp sora) with a 9 speed mtb cassette and derailleur (deore) so that she could have something a bit easier to spin up hills on. Works fine.

Ouija

Pull ratios are determined by the shifters, not the derailleur, hence the reason most 8 and 9 speed rear derailleurs can be swapped (if you stick with Shimano to Shimano and SRAM to SRAM). Things have changed with 10/11 speed on some rear derailleurs where the amount of movement for the amount of cable pulled is different to before. But with 9 speed and below the amount of movement has always been the same with Shimano (1:2) and SRAM (1:1) with only the shifter determining amount of movement.

rubertoe

I see a shimano sora rear mech on a 5 speed 1980's peugeot this morning.

Mechs are stupid and they only do what the shifters tell them, as long as the chain fits and an 8 speed chain will fit a 9 speed mech then it should be fine.

the Shimano shifters to shimano mech sorts out compatibility issues

generalcyclist

I replaced my cassette with the hg51 acera, which I believe is a mtb d/r ?

Since my rear d/r was a short cage, I replaced it with a medium cage Claris to make sure it can deal with the wide differences.

Main concern was the maximum strain when on both big rings, but it works great. It's given me a wider range to choose from, though I could probably do with the rear cassette starting at a bigger cog (smallest is 11 tooth). Shifters are shimano so gearing is working fine.

So it's been an improvement for me.

cyberknight

Do you need a bigger cassette , a long cage claris rear mech will cope with an 11-32 according to the blurb.

generalcyclist

cyberknight wrote:

Do you need a bigger cassette , a long cage claris rear mech will cope with an 11-32 according to the blurb.

My new cassette goes up to 30 and the medium cage claris derailleur copes no problem.
My front biggest ring is about 52 I think.