chainring - frame clearance
02gf74
Posts: 1,168
I have a Mondraker podium bike that has gone through a couple of iterations in the never ending quest to reduce the weight (9'44 kg currently). It is set up as 1x11 using SRAM components.
The last change dropped 40 g by replacing the SRAM X0 GXP chainset by SRAM carbon BB30 with the same direct mount 32T chainring, 6mm offset. This results in very little clearance between chainring and frame, about 1 mm. I put on a strip of insulation tape over the alloy protector and it got marked, not unexpectedly, due to flex. (Clearance measure to be just under 1.5mm)
Using a square piece of box section aluminium against the chainring, it lines up perfectly with the middle sprocket on the cassette which I think is correct. The cranks are about the same distance from the frame which is a good sign.
The small amount of clearance does not worry me but nethertheless I since made a spacer, 0.8 mm thick, to move the chainring a bit further out but am wondering if I should fit a chainring with less offset e.g. 3 mm?
Is my assumption that the chainring should line up with the middle of the cassette correct? I'd rather not move the chain out further as the terrain I ride seems to favour the larger sprockets.
The last change dropped 40 g by replacing the SRAM X0 GXP chainset by SRAM carbon BB30 with the same direct mount 32T chainring, 6mm offset. This results in very little clearance between chainring and frame, about 1 mm. I put on a strip of insulation tape over the alloy protector and it got marked, not unexpectedly, due to flex. (Clearance measure to be just under 1.5mm)
Using a square piece of box section aluminium against the chainring, it lines up perfectly with the middle sprocket on the cassette which I think is correct. The cranks are about the same distance from the frame which is a good sign.
The small amount of clearance does not worry me but nethertheless I since made a spacer, 0.8 mm thick, to move the chainring a bit further out but am wondering if I should fit a chainring with less offset e.g. 3 mm?
Is my assumption that the chainring should line up with the middle of the cassette correct? I'd rather not move the chain out further as the terrain I ride seems to favour the larger sprockets.
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Comments
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Photo to illustrate.
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You need to measure your chain line correctly, lots of info on line. It's an actual measurement in mm from the centre of the BB. There are tolerances so you can move the chain ring and still have the correct chain line.0
