So I installed my new lovely new FC-M985 cranks on my Cannondale Flash F3 Alloy, and noticed the clearance between the driveside crankarm and the chainstay is quite tight (about 3mm), but not critical.

I just wanted to confirm the tight 3mm clearance is acceptable for this crank? And I wonder what is the best case scenario for this crank since the q-factor is 3mm less on each side than the M980- ie most frames would have this same issue?

The bottom bracket is 73mm so I have one 2.5mm spacer on the driveside cup. I gather I can't cheat and add another spacer since the non-drive side wouldn't have enough spindle?

Other than that, amazing crank, light and very well finished!

Many thanks

3mm is fine. cranks dont flex much in that direction when in the rearmost position.

Many thanks for the reply thisisatest, pretty much what I was thinking/hoping.

I knew the M985 crank had a small q-factor, but I was surprised to see how small the clearance was! I can see these cranks wouldn't be compatible with a lot of frames eh?

just bought the same cranks, and my clearance is even less. 2mm max. don't know if it functionally matters, but just looking at it is a bit disconcerting. do you notice that your non-drive side has more clearance? the difference is noticeable on mine.

Yes, you're right the clearance on the non-drive side is about 4-5mm. Sounds like I'm not the only one then! I'm guessing this is the price you pay for a low q-factor.

As a follow-up to this I have noticed the drive-side crank arm on my M985 crank has a slight rub mark, as well as on the chainstay. Only very minor, but it is definitely making contact at some point.
So it seems the crank/frame is flexing and under certain conditions perhaps with additional mud there is a rub.

Not good, but do I need to worry about it? I'll post a pic.

I tried fitting one (44/30T) to a Trek 9.9 (2007/8?), and the large chainring fouls the chainstay before the crank seats against the BB bearing!
It might fit if I remove the chainsuck plate, but I'm not gonna risk that!

I've now fitted it to my SC Blur XC - it's very close on that - around 2-3mm max, but does fit.

Anyone else had the same issue with other frames?