Front chainring position

Discuss light weight issues concerning mountain bikes & parts.

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Location: Sunny UK

by 02GF74

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.

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.

by Weenie

Posts: 30
Joined: Fri Jul 28, 2017 12:34 am

by CycloTron

I would have thought that 1mm clearance with a 32T chainring would indicate something is not quite right.
What if you then wanted to go to a 34 or 36T chainring?
No way that would fit with your current setup and the bike should be able to comfortably accommodate such sizes.

Maybe check whether you need some BB spacers.

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