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I want to fit an MTB chainset into a Gravel Bike. Wouldn't be an issue if it was threaded 68mm BB, I could just fit MTB BB with an extra 5mm of spacers... No dice though, as it's BB86 BB shell.
So... Assuming a Shimano 24mm axled chainset, fit a PF41 BB but with an extra 6mm of spacers in total to the BB cups when fitting (reducing the insertion depth of the cups), or fit the BB so it's flush with the frame, and then use some 1" headset spacers or similar to space the difference between the outer face of the BB cups and the inner faces of the crank arms?
And before anyone asks why... I want to run a 36T ring with a 10-42T setup on a Gravel Bike with 700x50c tyres, on a frame optimised for 49mm chainline (New Shimano GRX Chainset or old non-Boost MTB chainset basically), and running a 4 arm 104BCD chainset that I have kicking around already just makes so much more sense to me than spending £150+ on a new one...
Do not reduce the insertion of the cups - that will potentially damage the frame and cranks once ridden. Use these instead:
https://www.wiggle.co.uk/race-face-x-type-chainline-spacer/?lang=en&curr=GBP
You could spend £90 ona GRX chanset - https://www.bike-components.de/en/Shimano/GRX-FC-RX600-1-Crankset-p72011/
You could spend £90 ona GRX chanset
40T ring is far too big for what I want sadly. It would be OK if I ditched SRAM xD for Shimano HG and got an 11-46 cassette instead, but thats added weight and I already have the wheels and a couple of part worn SRAM 11spd cassettes spare from MTB upgrades.
Do not reduce the insertion of the cups – that will potentially damage the frame and cranks once ridden. Use these instead:
Didn't know those were actually a genuine thing to be fair! Thanks... I was just going to bodge it with a 2mm and a 3mm 1" headset spacer, but this is obviously a far better option. Cheers!
Do not reduce the insertion of the cups – that will potentially damage the frame and cranks once ridden. Use these instead:
Just be aware a lot of axles taper slightly with the bit the bearing sits on being machined to exactly 24mm, and the rest being 23.something and unmachined. So you can't always do that.
I'd just get a set of s/h road compact cranks and a 36t chainring for those. You'll get the narrow Q-factor as well then.