A few modified bromptons on here already.
I've just bought an SL2-X.
I would like to put a Shimano or equivalent chainset & bottom bracket with the aim of saving a few grams. Has anyone done this already and come up with a bottom bracket size?
The stock BB on the Brompton has a 119 mm spindle.
However, as one who's tried swapping cranksets around on my M3L, I must caution you that the stock Stronglight cranks are surprisingly light. You may find replacing this stock crankset to be less of a benefit than you expect, unless you go the megabucks weight-weenie route.
You're posting twice - in BromptonTalk also. The Brompton crankset is light but not particularly stiff. The 3 challenges you will have is chain alignment, weight saving, and getting the right size teeth.
I investigated doing better, looked at the TA Vega, but its only slightly lighter and a high cost.
If you don't get chain alignment same as Brompton, any small % you save on weight you'll lose on chain drag.
A biggest weight saving is to swap the Bottom Bracket - I replaced with a TA Axix Light, I went for a slighter longer one and fitted a 30T inner chainring as granny-gear. The Titanium BB tends to creak with the Alu crankset. I'd recommend you leave the whole crankset as is.
Its not just a weight thing. I don't like the standard chainset to be honest - it looks cheap. I also think the shimano BB spin a bit more smoothly.
I quite like the Brompton-branded Stronglight, I think it has a sophisticated sheen, but if you don't like it fair enough.
Be super careful if you replace just the bottom bracket as the standard bottom bracket unit has ISO tapers. You could get a Phil Wood with Titanium axle, Aluminium alloy cups and light easy rolling ceramic bearings...
Another point to bear in mind is that if you replace the crankset you loose the stub that sticks out from the backside of the left hand crank. This recent 'innovation' on Brompton's part means that the folding pedal can no longer hit the bike frame and scratch the paint.
Last edited by Lewis Butler; 05-27-10 at 02:13 PM.
Reason: One of my words got starred out, brand of bottom bracket taken as offensive term so I have re-worded.