merlinrkd

Setting up a CADEX mountain bike for gravel. About a 1995 model. It is currently stock 7 speed with Shimano STX. Crank is 44-34-24. I have 9 speed wheels, cassette and chain. And going with Altus rapid fire style shifters. I plan on keeping the gearing in the same range. 11-28. My question is the rear derailleur. It's a medium cage STX that's obviously 7 speed. I have a rear Altus that is labeled as a 9 speed. Do you think the STX rear would handle the 7 to 9 speed conversion effectively or would in be better with the 9 speed Altus ? Usage is projected to be quite light. Couple light camping trips a year.

Andrew R Stewart 

Years ago Shimano made it known that their rear ders were backward compatible but not forwards so. Basically a der with greater cog count intention could sub for one designed for fewer cogs, but not the other way. This survived till10 speed stuff came out as the cable pull specs were the same from 7-9 cogs. I suggest you use the 9 speed Altus.

BTW I suspect the 7 speed freehub body of the STX rear hub could be too short to fit all 9 cogs. Shimano changed to a FH body with longer splines around their 8/9 cog systems. Andy

Bill Kapaun

It might work "good enough" or might not.
IF your chain has a Quik Link, a RDER swap after the fact is relatively simple.

A swap might require a new cable. Not a bad idea to change???

merlinrkd

Thanks Andy I was't clear. The project does involve a later wheel set. Those wheels are coming off my 91 Cannondale that is already a 27 speed. Your comments will inspire me to take a look at my 90's Trek hybrid that is now 27 speed. Don't know if that Der is compatible. thx

hokiefyd 

If you can get it configured (with limit screws) so that the derailleur will physically swing across the entire cassette, then I think it may work out okay. I have a 7-speed STX derailleur shifting an 8-of-9-on-7 cassette on a '97 Trek 750. It has a roller bearing hub and the freehub is not upgradable. So I'm using 8 of the 9 sprockets from a 9-speed cassette. My STX derailleur indexes pretty well with it. Of course, the total thickness of my cassette is not what a true 9-speed cluster would be...but the sprocket spacing is the same and the derailleur and 9-speed shifter (mine's a Microshift indexed thumby, but that shouldn't matter) seem to work pretty nicely with it.

Because of how easily all of this is swapped around, I'd give it a shot and try it. If it doesn't work, all your other stuff would stay the same (wheels, cassette, shifter, cable, etc.) and you'd just need to swap out the derailleur at the most (which you already have on standby). I think those old STX derailleurs look pretty nice and it'd be neat to get yours to work if it'll swing the whole cassette!

70sSanO

I would be really surprised if a 1995 7 speed STX RD would not have the range to cover a 9 speed cassette.

I have a couple STX 7 speed shifters and a couple STX RC 8 speed shifters. Not sure of the exact years, but by 1995 Shimano was moving on from 7 speed, except for their lower level offerings.

I would try it.

John

cyccommute 

The best way to find out is to just try it. Honestly, the way that derailers work, if the derailer is backwards compatible, it’s forward compatible.

merlinrkd

I'm mulling !! I'll need to start with a 9 speed chain. The STX Would use a shorter chain than the 9 speed Altus due to the medium cage. I was hung up on changing the chain length. Thanks to all your comments I have it figured. Set it up with the STX but leave the chain longer. If the STX works then just shorten the chain. If the STX issn't happy then switch the RD. THX all again!

merlinrkd

Went with Altus RD and shifters, 9 speed chain and cassette. Left the 7 speed crank. Seems to shift fine with a short run around the neighborhood-thx