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I'm looking for 165 mm length cranks for my Flaremax. The Cotic website states that 30-32 teeth chainring needs 52mm chainline. And 34-36 teeth = 55 mm. I can't see why the correct chainline would vary with chainring size unless there isn't physically space for a 34 tooth ring because of the curve of the chainstay.
Given it has a 148 mm rear axle, I would expect it to need a 55 mm chainline. But currently it has a 52mm chainline crank.
Haven't got the bike to hand to start measuring to confirm if this correct or not.
What am I missing?
Yeah it's chainstay clearance. Similar spec on my solarismax but I think the numbers are slightly different. I run a 52mm chainline with a 34t on that. Shifts perfectly. I run a 55mm chainline on my full suss because of clearance and it's definitely worse than the 52mm. Lowest gear skips in off when back pedalling. Pain in the arse, so I'm going to try downsizing the chainring and moving inboard on that one. Would go with the narrower chainline if I was you.
Thanks that makes sense. I'll get my ruler out later and double check.
After searching for ages it seems like some of the online places finally have some stock in
As others have said, it's chainstay clearance. However, chainring size does affect chainline on the theoretical scale in the same way chainstay length does. The larger the ring or the shorter the stay, the more extreme the chain angle at extremes and the more likely the chain will foul the 2nd smallest when in the smallest. This is then rectified with a wider chain line.
Have a word with Brant about his dodgy inbreds whose chainrings ground through their chainstay.
Definitely chainstay clearance - I've got a 34T oval on my flaremax, there's not much space between things! I run GX cranks which are 55mm chainline. Sigma have 165mm in stock for £100 at the mo
52mm chainline on a 148mm boost frame is best, 55mm isn't great on the biggest cog sprocket.
The bigger your chainring the more likely your need for 55mm chainline to avoid chainstay clearance issues.
I've some barely used 165mm Shimano 7120 cranks (55mm chainline) for sale if your interested, no chainring.