9 Speed Crank Set on a 7 Speed front Derailleur.

[stephan]

Okies I know the the 7/8 speed chain will work on the 9 Speed Chain Set, however will the indexing be ok with a Front 3 Speed Derailleur?

Current setup is a Shimano FC-M563 LX 7 Speed Chain Set - I am wanting to keep the 7 speed set up but just change to a 9 Speed Shimano FC-M750 XT Chain Set. On inspection the rings on the M750 look slightly closer together so I suspect the indexing will be off? Anyone tried this? (Triple Chain Set)

Bottom Bracket specs from manufacture that came with the bike are the FC-M563 LX Chain Set/Crank, and a Bottom Bracket of: BC 1.37 (English Thread, 68 and 107mm in length)

Cheers, any help suggestions welcome.

 

[Thias]

7/8 speed chain on a 9 speed set is no good. Because the 8spd chain is slightly thicker than 9spd. It works, but the shifting quality is bad.

The front derailleur is no problem though. I had M732 XT type front and rear derailleurs paired with a 9speed cassette+chain and M960 (XTR 9spd) STI set. No problems. The reason being that the "travel to cable haul ratio" is the same for basically all Shimano parts from 6spd up to 9spd. Maybe even 10spd but I haven't tried that personally yet. (There are some "irregularities" with Dura Ace though.)
That's why I love the old stuff and really don't like the new. You can mix and match all the parts. Even SRAM and Sachs and billet.

The one thing you have to keep in mind is, that the crank has to fit the front derailleur. Because there are two sizes for the front chainrings. And with that there are two types of derailleurs that have differently arched cages. I think it is called Microdrive.

 

[foz]

7/8 speed chains are all the same width, then they get progressively narrower from 9 speed up to 10, 11, etc.

There is usually some margin, and using sprockets/chainrings/chain with only 1 "speed" difference will probably work OK. I would try the new chainset, if shifting is bad then just swap the chain for a 9s and everything should work fine (even with the 7/8 speed cassette)

 

[Fourbikes]

I ran a 9 speed chainset on an otherwise 7 speed system and it worked ok. The only problem was that when in the middle chainring and one of the two smallest sprockets at the rear, the chain would rub on the larger chainring. A narrower 9 speed chain solved the problem.

 

[Splatter Paint]

https://www.sheldonbrown.com/speeds.html

 

[stephan]

I ran a 9 speed chainset on an otherwise 7 speed system and it worked ok. The only problem was that when in the middle chainring and one of the two smallest sprockets at the rear, the chain would rub on the larger chainring. A narrower 9 speed chain solved the problem.

Thats interesting and would suggest the chain line was out slightly, do you recall the axle width you used, was it the original 7 speed axle? The 7 speed M563 axle I have is 107mm, however the 9 speed M750 according to the chart below requires an axel to be 110-113. If this is the case your 9 speed chain did not rub because of the smaller tolerance, where if I bought say a 110 axle rather than use the 107 axle and a 7 speed chain this should make up that difference in the chain alignment. I guess its hard to tell without trying things.

Thank's to https://www.sheldonbrown.com for this chart below.

 

[dirttorpedo]

Front derailleurs are dumb so I wouldn't look to it for problems. If the spacing is different between rings it will be the front shifter that will cause issues.

 

[bikeworkshop]

Chainstay length also makes a difference - and some dérailleurs are more tolerant than others.
easiest way to see if it's ok is to try it.
You'll almost certainly find it can be set up to be quite usable, but slightly more cross-chaining rub, shifting not quite so precise.

 

[Fourbikes]

Thats interesting and would suggest the chain line was out slightly, do you recall the axel width you used, was it the original 7 speed axel? The 7 speed M563 axel I have is 107mm, however the 9 speed M750 according to the chart below requires an axel to be 110-113. If this is the case your 9 speed chain did not rub because of the smaller tolerance, where if I bought say a 110 axel rather than use the 107 axel and a 7 speed chain this should make up that difference in the chain alignment. I guess its hard to tell without trying things.

I was using the original 113mm axle and went from an STX MC30 to an LX M570, which I think was still the correct length. A shorter bottom bracket, would make it worse, as the chainline would be more acute (less straight).

 

[stephan]

Front derailleurs are dumb so I wouldn't look to it for problems. If the spacing is different between rings it will be the front shifter that will cause issues.

So maybe it requires a 110mm axle and a new 3 speed front derailleur to compensate - I never actually thought about swapping the 3 speed front derailleur to say a (9 speed - albeit 3 speed ) M750 one. (however would a 7 speed chain fit through it) problem maybe solved then presents another one - (I read someone used spaces on the 9 speed chain rings to compensate, however having a look at that it would look messy and through everything out)