9 Speed Crank Set on a 7 Speed front Derailleur.

[stephan]

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).

I would be replacing with a 3mm longer one. 107 --> 110mm

 

[stephan]

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.

Thanks, I don't think the derailleur is "Microdrive" - just a standard front mech for both chain sets. I think am swaying on getting a 9 speed chain, and going from a 107mm axle to a 110mm axle as per what the chart states for that M750 crank. (Running a 7 speed cassette, 7 speed rear mech and 7 speed front mech) Hopefully I can make it work.

 

[CassidyAce]

... 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 ...

The 7 speed chain will fit through the front derailleur but it's not ideal. I tried it once but never again. The chain rub on the front mech was the problem. I was having to trim the front mech with every second shift at the rear. Shift from 4 to 5: fine. 5 to 6: trim. 6 to 7: fine. And the same when shifting in the opposite direction at the back. I was able to trim the front mech because I was using GripShift with that facility but I found it so frustrating that I quickly changed the front mech. This was on a 3 x 8, 26" MTB. Something with longer chainstays would reduce the problem but I don't know if it would eliminate it.

 

[stephan]

The 7 speed chain will fit through the front derailleur but it's not ideal. I tried it once but never again. The chain rub on the front mech was the problem. I was having to trim the front mech with every second shift at the rear. Shift from 4 to 5: fine. 5 to 6: trim. 6 to 7: fine. And the same when shifting in the opposite direction at the back. I was able to trim the front mech because I was using GripShift with that facility but I found it so frustrating that I quickly changed the front mech. This was on a 3 x 8, 26" MTB. Something with longer chainstays would reduce the problem but I don't know if it would eliminate it.

Thanks for this, I will prob try a 9 speed chain on the set up. The issue is I need to decide on the axle length which I will probably go for the 110mm to try and keep the chain line. Those BB's are expensive now for a decent Japanese one so I am not wanting to try and make a mistake with the purchase as they are non-refundable. (as expected on such products)

 

[stephan]

"The crankset being used determines spindle length, not the frame" Apparently Dr Google keep's telling me this.

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

 

[dirttorpedo]

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)

I set up my Miyata triple cross as 9 speed and ran it with old 7 speed front and rear mechs and a 3x7 chainset with no issues. I was running the front shifter friction though so indexing was not an issue. I can't see why a 9 speed chainset would be any different with a friction front or a 9 speed front shifter. The only possible issue is if the 3x7 front mech didn't have sufficient range to cover the 3x9 chainset (and I can't imagine that would be an issue if the 3x9 chainset has narrower spacing between rings). The width difference between 6/7/8 and 9 speed chains is small so I can't see chain width being an issue for the front mech cage.

Can't help you with the spindle length - I would go with whatever is recommended for the chainset in question.

Of course you could just keep running the 3x7 chainset and save yourself the cost and hassle of an upgrade with little performance benefit.

 

[stephan]

I set up my Miyata triple cross as 9 speed and ran it with old 7 speed front and rear mechs and a 3x7 chainset with no issues. I was running the front shifter friction though so indexing was not an issue. I can't see why a 9 speed chainset would be any different with a friction front or a 9 speed front shifter. The only possible issue is if the 3x7 front mech didn't have sufficient range to cover the 3x9 chainset (and I can't imagine that would be an issue if the 3x9 chainset has narrower spacing between rings). The width difference between 6/7/8 and 9 speed chains is small so I can't see chain width being an issue for the front mech cage.

Can't help you with the spindle length - I would go with whatever is recommended for the chainset in question.

Of course you could just keep running the 3x7 chainset and save yourself the cost and hassle of an upgrade with little performance benefit.

Thanks for that reply, I have already bought the XT chain set. If I run a 9 speed chain with the front 7 speed mech, and if the mech is out of sync, I then have an option of running a 9 speed front down pull mech as I will already be running the 9 speed chain I guess. Cheers Stephan.

Bike is here: https://www.retrobike.co.uk/threads/cannondale-m800-light-project.473472/

 

[Thias]

Why did you want to use a 9spd chain on a 7spd setup? If everything other than the crank is 7spd, even the cassette, just use a 7/8spd chain and be happy. 7spd cassette+ 9spd chain is not a good match. Except you have 9spd chain already on the shelf, but don't have the 20 quid to buy a new chain. On the other hand, 7/9spd chain on 9spd crank is no probelm at all, because the "inner" diameter of both 9 and 7spd chains is the same. Only the outer diameter is different, hence the problems that araise using 9spd chain on 7spd setups.

 

[stephan]

Why did you want to use a 9spd chain on a 7spd setup? If everything other than the crank is 7spd, even the cassette, just use a 7/8spd chain and be happy. 7spd cassette+ 9spd chain is not a good match. Except you have 9spd chain already on the shelf, but don't have the 20 quid to buy a new chain. On the other hand, 7/9spd chain on 9spd crank is no probelm at all, because the "inner" diameter of both 9 and 7spd chains is the same. Only the outer diameter is different, hence the problems that araise using 9spd chain on 7spd setups.

Hi Thias, I think you picked up the thread wrong. I have a 9 Speed Chain Set/Crank on the shelf and a 7/8 Speed chain on the shelf. I was asking if the front 7 Speed Mech would transfer the 7/8 Speed chain to the 9 Speed Chain Set/Crank ok. There is a previous reply where someone had to change to a 9 Speed Chain as the chain rings are closer together on the 9 Speed Chain Set/Crank and the 7/8 Speed Chain was fouling the chainrings in some gears.

 

[Thias]

Ok. So I indeed misunderstood your question. I never had the problem, that a 8spd chain would rub on the neighboring crank chainrings. Although that may be due to me usually not using the full "range" of gears. I tend to avoid the "extremes" like smallest front to smallest rear.
I do remember thou, that I once had to shim one of the crank chainrings to get them further apart.