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-   -   Crank ring spacing 7/8 vs 9 speed crankset (http://www.bikeforums.net/mountain-biking/933389-crank-ring-spacing-7-8-vs-9-speed-crankset.html)

awfulwaffle 02-08-14 01:24 PM

Crank ring spacing 7/8 vs 9 speed crankset
 
Hello again folks,

Back to pick your collective brains! I use my trusty ol' frankenbike for both winter as well as trail riding (and formerly for year round commuting before I got my road bike), and the drivetrain is getting pretty tired. After riding this winter, all the snow and salt has started taking a noticeable toll despite my best efforts to clean everything up after I ride. Not to mention the parts that I used when putting the bike together are 2006 Acera 3x7 components which had been in use for quite a while before I wrecked really hard as a kid and decided to take a break from mountain biking. So, I recently began investing in a 9 speed upgrade. Thus far I've got a set of SRAM X9 ball bearing shifters, with an X7 rear and X5 front derailleurs, PG-970 cassette and a chain on the way.

As money doesn't grow on trees, and the crankset being the most expensive part of this upgrade, I wonder if I can get away with using my old one for a while. Looking online, I've seen some people say a 7/8 speed crankset will work OK with this setup (with front shifting being a bit tedious but doable), while others say that it won't work at all. So, my question(s) to you:

From personal experience, can anyone confirm or deny whether such a thing will work? Or, alternatively, can anyone definitively quote the chainring spacing difference between 7/8 and 9 speed cranksets? I can't seem to locate it online, even on Sheldon Brown's site.

My backup plan at this point is to run it as a 1x9 until I can afford a decent 9 speed crankset, since I don't leave the middle chainring on the trail unless I'm fighting a particularly steep climb.

Thanks in advance for your input!

Canker 02-08-14 09:34 PM

It isn't a problem.

BenPS 02-09-14 12:34 PM

^that. Chain size is different between 7/8 and 9, but ring size doesn't change. You'll be fine.

Although with a new chain, new cassette, and new der., having old, worn chainrings will cause your chain to wear a little more, and it might skip every now and then. So replace when you can -- but in the mean time, just ride

awfulwaffle 02-09-14 06:20 PM

Awesome, thanks guys. I've bought a lightly used chain on CL in anticipation, can't wait to get the bike together!

roccobike 02-10-14 06:13 PM

Been there, done that swap, no problem using the 7 speed cranks.


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