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Old 09-30-12, 11:08 PM   #1
mtnbke
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Want to use 10 speed triple mountain bike crank w/SRAM X.9 components which are 9sp

Okay, I've got a mountain bike which I can't comfortably ride because the cranks are too small. I want to replace them w/180mm cranks. I ride 205mm cranks on my road bike, so don't bother posting that there isn't a difference as I'm not an average size cyclist. The 175mm cranks make me miserable trying to climb any kind of hill even with low gears. You try riding 165mm cranks if you don't think it would matter.

The problem is that I just bought the bike. It came with SRAM X.9 9 speed components and an SRAM/Truvativ Stylo crank with 175mm crank arms.

I want to know if I can use a 3x10 crank or if a 3x9 crank would shift better. Of the cranks I want, Race Face Turbine the 3x9 is more expensive by about $75 than the 3x10 where I'll be buying it.

Now here is the punchline: I'm not going to be using the SRAM X.9 front shifter. I hate not having adjustable front trim, so I'll probably be using an old XT thumbshifter or something similar. Not worried about whether the SRAM X.9 shifter will align correctly, as I won't be using it. I am worried about whether using the XT friction shifter whether a 3x10 crank would shift poorly with a 9 speed chain. I don't want to use a 10 speed chain as I'm a pretty big cyclist and already I'm worried about breaking chains.

Which leads to another question: What is the difference between a 3x8 crank a 3x9 crank and a 3x10 crank, aside from the rings (and whether the BB is square taper or external)? Is the spacing from the center of the tooth to the center of the tooth on the higher and lower rings (on a triple) the same on 8sp, 9sp, and 10sp cranks? I'm wondering if the cranks are like cassettes where the spacing becomes narrower.

The reason I ask is I might completely convert to an 8sp drivetrain to get the stronge/thicker chain/rings/cogs. So if I could use an 8sp crank w/modern rings that would be a flexible option as well. So could I use a 10sp crank w/8sp rings?
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Old 09-30-12, 11:15 PM   #2
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Cranks aren't any "speed", it's all essentially in the rings. If the "speed" rings you need fit the crank, all is good.

There are some spacing differences, but as far as I know those usually only apply to mid to higher end road doubles.
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Old 10-01-12, 09:46 AM   #3
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You are saying that the spacing positioning the rings on triple cranks has gone unchanged from a 6/7/8 crank to 9, and now 10? That the cranks all position the center of the rings exactly the same distance apart? I'm not sure that's entirely true.

With chains getting narrower in profile things would have needed to keep proportional wouldn't they? If the chain was reduced in width 10% would they really have kept the c-c distance between the rings the same throw?
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Old 10-01-12, 09:56 AM   #4
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At our bike coop, we play around with all sorts of weird combos. I have 2 9speed brifter equipped bikes that have an old triple and double on them. Stuff from the early '90s. They work fine.

My buddy at the coop has an Bianchi Eros that he put a 10 speed drive train on. He replaced the downtube shifters with modern 10 speed brifters, rear cassette with 10 speed cassette, and 10sp chain. The front crankset is an old Campy crankset from the early '80s. Before he put the Campy crankset on there, he had a '70s era Stronglight from a Peugeot on there with the 10sp components and it shifted fine. Also for the record, the rear derailleur is a nice older Shimano 600 (or is it 105?) that shifts the 10sp cassette fine.

The spacing may not be exactly the same but the front is where you have some fudge room.
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