Bicycle Mechanics - using a 9 speed crankset on a 7 speed setup

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xtree
05-22-09, 05:12 AM
I have a Raleigh M50 mountain bike and the rear derailleur cratered. I purchased a new rear derailleur and while I'm changing this I am thinking about changing the front crankset and deraillleur. I was thinking about upgrading to a Shimano Deore M532 crankset. My bike is a 7 speed, the current BB is a 68x116. I'd also like to replace my front derailleur with a Deore. Later on I would like to replace my rear wheel and cartridge. I was wondering if the M532 would work with my current setup, would it be safe to use a Deore FD? Thanks for any advise..

joejack951
05-22-09, 02:57 PM
If you want to use a 9 speed crankset, you will also need to use a 9 speed chain. Using the 9 speed front derailler in conjunction with these items will offer the best shifting performance but your current front derailler will also work.
laura*
05-22-09, 04:11 PM
I am running a 9 speed crankset on a 7 speed bike just fine. The chain is 6-7-8 speed chain. The FD, shifters, cassette, and freehub are all 7 speed. The RD is 9 speed, but that's because none of the older good quality RD's are speced to handle a 34 tooth cassette cog.

fuzz2050
05-22-09, 04:53 PM
The RD is 9 speed, but that's because none of the older good quality RD's are speced to handle a 34 tooth cassette cog.

Please, there was the Duopar, by Huret. And the Duopar-Eco, the cheap version...and I think Suntour made a model...

ok, you may have a point
joejack951
05-22-09, 05:06 PM
When I tried to run an 8 speed chain on 9 speed rings anything but a perfect chainline resulted in the chain getting caught on the ramps and attempting to self-shift. Perhaps it depends on the rings though. The rings I had problems with were Shimano on a triple road crankset. No other experience with that mix of components.
laura*
05-22-09, 05:33 PM
Please, there was the Duopar, by Huret. And the Duopar-Eco, the cheap version...and I think Suntour made a model...

ok, you may have a point

Oops, I should have included the word Shimano in there. Let me rephrase:

I couldn't find a Shimano RD of STX/Deore quality or better that was rated for a 34 tooth cog (and 43 teeth of wrap) that wasn't part of a 9 speed group.
xtree
05-23-09, 05:02 AM
Thanks everyone.
laura*
05-23-09, 06:45 AM
Perhaps it depends on the rings though. The rings I had problems with were Shimano on a triple road crankset.

Hmmm. Thinking. Aha! Yes, I bet it does depend upon the rings. I'm running a Shimano triple mountain crankset on (of course) an MTB.


When I tried to run an 8 speed chain on 9 speed rings anything but a perfect chainline resulted in the chain getting caught on the ramps and attempting to self-shift.

With an MTB's smaller chainrings, it'd be so much harder for the chain to rub against the next larger chainring, even when cross chained. Plus, an MTB crankset is further to the right relative to the cassette than on a road bike. This makes the bad chain angles all to the inside (lower gears, larger cogs). Because the next smaller chainring is, well, smaller, the chain can't hit it.