Front derailleur: 7/8/9/10 speed compatibility?

[Amanda P]

I do try to keep up, but I need advice on this one.

I want to upgrade a bike from a single chainring to a double (or maybe triple). It has a 7-speed cassette, and I'm in no hurry to replace the rear hub, so it's likely to stay that way.

My question is: should I look specifically for a 7 or 8-speed front derailleur on the grounds that a 10-speed one will have a narrow cage for narrow 10-speed chains? Or will an 8-speed chain run through it fine?

Either way, reccommendations? The bike's running 105 and equivalentish components elsewhere, so that's the sort of level I'm afer.

 

[Stick on a Giant]

Phil, I haven't tried this at home, but I wouldn't think it would matter too much as far as the derailleur is concerned - the chain doesn't 'fit' tightly in the cage, and as long as a 7 speed cassette takes up as much room as a 9 or 10, which I think it does, there shouldn't be an issue with the angle the chain goes through the cage.

What you probably do need to check, is whether you can a) buy a 7 speed front chainset or whether a new 105, ie 10 speed, chainset will run OK with a 7 speed chain - and I don't know the answer to that!

 

[Landslide]

FWIW...

I'm currently running an 8spd chain and cassette using a 9spd Tiagra front mech.
To further test Shimano's theories of incompatibility I'm using 24/36/46 chainrings (supposedly too small for the mech.

It all works fine when I remember to lube the cables...

 

[TheDoctor]

I've run 7 speed chain (Sram) through a 9 speed Mirage front mech before now, in an otherwise Shimano setup. It worked well enough, or as well as it had any right to, given the mishmash of stuff.

@Landslide - what chainset are you using? i assume it's an MTB one, as I don't think 36T 110 pcd rings are doable, unless they're pentagons rather than rings!

Currently running 48/38/24 on a Sora, with 13-26 at the back. Anything that won't get me up, I'd need crampons.

 

[Landslide]

(Pre-compact drive) Shimano Exage, 74/110mm BCD. Sheldon (God rest his soul) reckons you can go as low as 33T on 110.

 

[andy_wrx]

26/36/46 sounds like an old-skool 7sp MTB chainset, which are I think 110
36T on 110 BCD is quite normal, most road compacts are 36 or 34/50
But yes a road triple is normally 130 BCD not 110 and so you'd only get 38

I ran Sora 8sp shifters (no trim capability) with a Sugino triple chainset, 8sp chain and 9sp 105 front mech for a while, worked fine but was a bit awkward to set-up to avoid chain rub (not problem, just annoying - could set it to rub on inside or outside or even both sides but never managed to use middle ring and all 8 on the cassette)
Switched to 9sp chain and it was fine - suspect the 9sp mech plates are narrowed-together than an 8sp would be and so it works better with the narrower chain

 

[bonj2]

i didn't think it mattered too much but i had an 8sp one when i upgraded to 9sp, and it shifted ok, but not brilliantly. I've now got an ultegra 9sp one and it shifts pretty well.

 

[TheDoctor]

@Landslide and Andy - I was thinking road, so i did mean 130 mm PCD. 33T 110 mm PCD rings are indeed available, C+ reviewed them recently.

Don't see why we can't use 110 for everything. Life would be easier!