Hi, since changing my cranks and chainring, my transmission sounds bloody awful in the largest four sprockets on the cassette, especially in a bit of mud. I'm guessing the chainline is incorrect and could do with some advice before I spend money trying to fix it. Any help much appreciated!
The frame is a 2017 Trek Stache 9.8. This has boost spacing at the back, with a 148mm Hope Pro 4 rear hub and Sram GX 10-42 11-speed cassette. The bottom bracket is non-boost, however - it's a standard Hope PF92.
The crank is a 2016 Sram XX1 GXP standard / non-boost, which I installed on the bike (so it's not standard equipment).
The chainring is a Chromag Sequence DM 30t boost chainring with a 3mm offset (like this: http://www.chainreactioncycles.com/chromag-sequence-dm-boost-chainring/rp-prod155526)
When using the largest four sprockets on the cassette, it sounds like the chainline is wrong and the chain is grinding on the chainring as it engages.
The data in the table at the foot of this page ( http://www.chromagbikes.com/chainrings/sequence) on the Chromag website suggests an 6mm offset ring is actually correct rather than 3mm.
Compared to the 3mm offset ring I already have, would this bring the chainline another 3mm further inwards towards the centre of the bottom bracket, or move it an extra 3mm further away from the centre of the bottom bracket?
To improve the chainline and stop the grinding I hear when in the largest four sprockets, I think I probably need to bring the chainring slightly further inwards towards the centre of the bike.
Thanks v much,
Nic
6mm offset is non-boost and will bring your chainline closer to the BB. I use a non boost chainring on my boost hub as it gives a better chainline and shift.
You might want to make sure you have enough tire clearance if you are bringing your chain closer to the tire.
@mikeep, thanks, that's what I thought / hoped. I have decent clearance to the tyre so will probably give that a go. Cheers!