Discuss light weight issues concerning mountain bikes & parts.

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Posts: 187
Joined: Sun Feb 03, 2008 4:40 pm
Location: Singapore

by seismic

I am riding an old Cannondale Flash Carbon 26" from 2009 and contemplating putting on a THM M3 crank set. I can understand that I should get the THM BB for the BB30 and that it should fit the frame. At the same time, I am considering shifting my drive train to XX1. As far as I can understand I should be running a 36T chainring when riding a 26" in order to have a fair gear ratio. Do anyone have any idea if my frame can take a THM M3 cranks with a XX1 spider and a 36T without the chainring getting too close to the chain stays?

Any other issues to consider?

I know it is properly a faaaaar shot to expect that someone knows, but as advised by a fellow WW previously, - that is what a forum is for anyways.

Thank you


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Location: Europe

by mythical

I'm not sure which BB shell dimensions your '09 Flash Carbon has, but when it's Ø42x72mm, then you should order the THM BB30 MTB bottom bracket.

If Ø46x72mm, then the THM PF30 MTB version. If it's 68mm, then you might need to resort to a THM Road BB.

I don't see why a double ring setup wouldn't clear the chain stay and with XX1 you'll only use a single narrow-wide chainring. A 36T is large enough to clear the outside diameter of a 104BCD spider, so it doesn't bring the chainring further towards the chain stay in compared to a double setup. In fact, you might be able to mount it on the outside position, depending on how it influences the chain line.

Your THM cranks should end up looking something like this:

You'll be fine in upgrading to a THM M3 crankset, also with a 36T chainring XX1 setup. Just make sure you get the correct specification BB. :thumbup:

Here are a few images of chainring clearance with your desired setup on an Open 29er frame:
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