alfred mcdougal

I have a Shimano RD-M531-S 9 speed rear derailleur and Shimano CS-HG70 7 speed cassette. What index shifters will work with this combination?

DX-MAN

The only thing special about the "9-speed" derailleur is that it'll take the skinnier 9-speed chain.

You need a 7-speed Shimano-compatible shifter.

joejack951

I wouldn't even give it that much credit. Skinny chains work just fine with deraillers designed for 7 and 8 speed in my experience.

fuzz2050

It's only going backwards that it can become an issue. A 6/7/8 speed chain on a 9/10/11 speed derailer isn't the best idea.

joejack951

Why not? I've measured the cages and they are pretty much the same width (speaking of RD). Up front, I'm completely in agreement.

alfred mcdougal

Why? Specific details please.

I went to a LBS for sound advice and the LBS mechanic's advice is contrary to yours... which was: "An 8 speed SRAM chain will work fine with a 9 speed derailleur." Feel free to prove him wrong with facts. I'm open for info... I just want to build a 7-9 speed rig that works.

One problem with internet forums is a reader would never know the skill level of random anonymous posters.

alfred mcdougal

More info

The hub: Shimano STX RC model FH-MC33. I believe this is a 7 speed hub manufactured around 1994-95. At least, that is what the mechanic claimed.

Gonzo Bob

+1 - I run a 6/7-speed chain on a 7-speed cassette using a "9-speed" rear derailer (MD510). It works great.

I also use a narrow cage 9-speed derailer up front. It works fine but does need trim adjusted with rear shifting more often. I have bar-end shifters so trim adjustment is not a pain.

To OP: Any non-Dura-Ace Shimano compatible 7-speed shifters will work.

Retro Grouch 

I'm not the kind of guy who measures stuff like this unless I encounter a problem. I seem to remember reading somewhere, however, that the inside chain dimension is the same. All the narrowerness is made up in the outer plate design.

joejack951

Perhaps you should look elsewhere for free advice then.

ls01

you can use a 7 or an 8 speed shimano index shifter. the cassettes are the same spacing if I remember right. the dedrailer wont care either way. 9 speed and up uses a thinner chain. Although I have heard some people say you can use an 8 speed chain on a 9 speed set up MY one and only attempt to do this resulted in excessive chain noise, rub, and front trimming.
for the front you need to use the derailure designed for the chain width you are running to get the proper amount of trimming etc. with index shifting. If you run a ten speed chain and an 8 speed f.derailure you will ned to move the derailure excesively to get it to shift. but an 8 speed chain and a ten speed derailure will need to be trimmed more frequently or it will rub alot.
I have also heard that a 10 speed chain can get caught in between the front rings of an 8 or 9 speed set up. The rumor is that the middle or small ring of a 10 speed set is offset to be closer to the big ring to keep this from happening.
mix and match to satisfy yourself. just dont expect it to be perfect. you will have to make some allowances

Ex Pres 

Chains are one place where Campy trumps Shimano in compatibilty (Shimano wins on freehubs). The Campy C9 chain is backward compatible, per factory, with Campy's 7 & 8 speed. Shimano, OTOH, recommends that you not use their 9s chain on 8 (and lower) speed setups.

Since you are using a Shimano 7s cassette Shimano would recommend using a 7/8 speed chain. And find a (non DA) 7s shifter. 7s = 5.0mm cog spacing. 8s = 4.8mm, so you can set up the 7 much easier.

In my own personal experience mixing front and rear derailleurs w/shifters that didn't "match", I've had much better luck running Campy 10s front derailleurs w/8s Shimano STI shifters and 8s chain combos. I've done this on two bikes. I had the Campys in the parts box, so I tried it and liked it. The newer (9/10) Shimano FDs just were never right w/this setup. YMMV.

DMF 

There's something to this. 5-11 speed chains are the same inside where they meet the cogs, but the overall width of the chains outside varies.

A 5-speed chain will work just fine on a 10-speed cassette - the cassette only sees the inside.

Edit: Wrong. It fits the cog, but there is interference from the adjacent cog. See discussion below.

But a derailleur sees only the outside. A derailleur designed for a narrow chain will have narrower cages and may have problems with a wide chain, and vice versa.


In practice, though, there's probably enough slop that it won't make a huge difference. But try to keep the widths of the chain and derailleurs the same if you can.

Al1943

7-speed is 5.0 mm, 8-speed is 4.8mm. I would not recommend 8-speed shifters with a 7-speed cassette. You might be able to make it work by lining up the shifting in the middle of the cassette but the .2mm error will be cumulative as you approach the left or right side of the cassette.
Here is a chart: https://www.ctc.org.uk/DesktopDefault...D=3946#Shimano

DMF 

Interesting article. Thanks!

ls01

Like I said at the end of my post. it wont be perfect. I have done this on two bikes and they worked quite well. one is still being ridden almost daily. If you start in the middle in either direction you are only off about a half a mm. at the extreem. not even enough to make any noise.
If you want perfect then stick to the series components you are building. you can mix groupo's 7,8,9 or10, for the most part. The exception is certain D/A parts which are D/A only. most other parts will work together.
As with most things there is a learning curve involved in mixing parts. just go slow and do the reserch before buying.

Noobert

Can you use a 7 speed indexing shifter with a 8 speed cassette?

Retro Grouch 

Doesn't the rear derailleur guide the chain via the jockey pulleys from the inside? I'm also thinking that a too wide chain is going to have cog-to-cog interference at the cassette.

Retro Grouch 

I think that it depends on how picky you are.

I've tried mixing and matching various combinations of 7 and 8-speed parts many times over the years. I can get it to work perfectly for a short term and I can make it kind'a work over a longer term. I've never been able to get it to index to my satisfaction for an extended period.

DMF 

You have a point. The cage doesn't do the actual shifting at the rear like it does in the front. But there might still be interference and "play" issues. The pulleys themselves, though, are like cogs in how they "see" the chain.

Cog-to-cog interference is possible if the spacing is too narrow, but so far doesn't seem to be a critical issue. 5-speed pin width is 7.2mm, so theoretically could function with >3.6mm spacing. Closest current spacing is 3.85mm. (Pitch chart)

Edit: Wrong - neglects adjacent cog width. See below.


I'll bet cross-chaining with a wide cassette would be noisy, though.
Maybe 12-speed will be different.


Hey, I wouldn't put a 5-speed chain on a C11, so don't quote me.

Noobert

Another one: What about 5 speed index shifter on 7 speed freewheel?

ls01

the derailure is "told" how much to move by the shifter. so if the shifter is matched to the cassettes spacing, and the derailure has enough travel, it should work. this applys to shimano which is what I am most familiar with. and barring certain dura ace parts. and yes the chain should also be thin enough for your application. A thinner chain will work with wider ( lower gear numbers) spaced components to some extent, as far as the rear is concerned. but then you have to be careful about which rings and derailure you use in the front. The front derailure will need to match the chain used. To keep the throw of the front derailure correct for shifting and trim. Also there is a common belief that a 10 speed chain can jam between the rings on older stuff. As I understand it the fix is to swap the small ring out for a 10 speed specific one as the teeth are offset towards the big ring. It also helps to have this ring in the proper position for shifting, and trimming.
Wider chains on thinner spaced components wont work that well. on the rear it will cause noise due to chain rubbing on the adjacent cogs on the cassettte and in the front it will result in chain rub on the f.derailure and excesive trimming.

ls01

5 speed indexing?

norwood

For the OP. I have several bikes set up with Shimano 9spd RD's on a 7spd cassette and one with a 8spd RD on a 7spd. All work great. As for shifters, if you have a 7spd cassette, you need 7spd index shifters. Or a friction setup. Of course then again the OP doesn't know my skill level, so take for what it's worth.

rogerstg

Except that the spacing refers to center to center and does not account for the cog width of ~1.9mm
Trying to run a 5 speed chain on a 9 speed won't work because there is only 7.2mm of space for the 7.2mm chain. When a chain rubs on the next larger cog, the ramp causes it to shift (downshift) for part of a revolution until the rd forces it back onto the higher gear. This happens with each revolution.