Brompton FAG Bottom Bracket

[Pickled Onion]

The FAG BB is no longer available, and the advice on SJS is to buy a whole new chainset.

What's the recommended replacement?

[rogerzilla]

Good old SJS!

Are you keeping the swaged chainset?  If so, you need an ISO BB (Campag?) with the same RH protrusion.  For best results take the old BB to the shop.  I have a FAG tool I'll never use again, if you don't.

Alternative chainsets are problematic on the LH side because the folding pedal won't go over the end of beefier cranks.  If you use SPDs or demountable pedals, this isn't a concern.

[Pickled Onion]

It's not mine, a colleague's. I can lend him a FAG tool to get it off, but ISO BB's are like hen's teeth nowadays... you can get them in the campag lengths like 111, 115, but FAG was 119.

What are the implications of just sticking a JIS taper BB on there?

[LittleWheelsandBig]

Depending on tolerances, each crank may sit 1-2mm further out on the taper. An older crank may have opened up the taper a bit, so the effect may be less apparent.

[Shreds]

I had my BB and cranks replaced immediately I bought my last Brompton; lighter, stronger; less flex; including adding superb carbon fibre crank set up. It makes such a difference to the pedalling. I would do it again without a shadow of doubt despite the cost and the slightly awkward installation.

Brompton just never seem to get the message about significantly reducing weight whilst retaining durability, although Steve Parry used to create some interesting and lightweight SP Bromptons' back in the day.

A Brompton is a bike that needs to be carried on numerous occasions, so the weight is crucial.

[LittleWheelsandBig]

I've never found that flexible or stiff cranks (or stems or frames) made any difference to speed when I was racing on the velodrome and road. Our bones, ligaments and tendons aren't infinitely stiff after all but YMMV

[grams]

What after market cranks are significantly lighter than the stock ones all in?

[rogerzilla]

Not many - the stock cranks are very flimsy and the crank can shear from the ring if you give it some beans away from traffic lights.  You'd probably have to go for carbon fibre or HT2, which would give you hideous chainline problems with the required BB.

[LittleWheelsandBig]

The modern Brompton cranks don't have a swaged joint any more but are a bit heavier.