Sorry for the thin information. Here’s the full story.

I’m trying to install a Hollowtech II bottom bracket and double chainring (50/34) crankset on a Brompton. My idea is to manually move the chain to the small chainring for climbs and big ring for flats.

The shell of the Brompton is 68mm. The challenge is that, without the spacers, the rear triangle of the Brompton interferes with the small ring when the bike is folded.

4mm of spacers gives me good clearance but not enough spline engagement. I switched to 1.5mm spacer and the engagement is better. (photo below).



The plastic safety tab does drop flush. But, I still can’t fold the bike if the chain is in the small ring.

Not sure if I’ll keep it like this or go back to square taper but it’s an interesting project.