Brompton 6-Speed Hub Compatibility

[sizbut]

18-year old rear wheel is finally dying - cracks in the rim and some nasty sounds. How confident can I be that a new 6-speed rear wheel is compatible with the spacing and controls on an 18-year old frame?

[Brucey]

The new wheel will fit in the frame OK but Brompton have changed from a SRAM hub to their own [SA] BWR hub; IIRC both the gearing and the shifters are a bit different. My advice would be to get the old wheel rebuilt, provided there is nothing wrong with your old hub and you can still get cogs for it, etc. If the hub needs attention too then maybe convert but in fact all is not lost; most of your hub is identical to a 'torpedo' of similar vintage.

[rogerzilla]

Brompton's old plastic rear shifter used to work for both SA or SRAM hubs so it should be ok once you replace the SRAM indicator "grabber" with a normal SA toggle adjuster.

A bigger issue may be that SA BWR hubs have bigger internal ratios and different sprocket sizes, which you may not like much.

Keeping the SRAM hub is an option but parts are becoming unobtainium, particularly sprockets and bearing cages. I prefer the old setup with 13/15t sprockets and a 1.35 (ish) internal ratio, so bought a small supply of spares while they were still around.

[hoogerbooger]

Yes the original 15t/13t sprockets are now harder to find than hen's teeth......so this is definitely a factor to consider. Unless perhaps you do very few miles and your existing sprockets run fine with a new chain.

I went from an SRAM 6 speed to a BWR 6 speed and found the gaps between gears too big for my liking.....even in a hilly area where the extra gear range was useful.

(BWR worked fine with my 2005 Brompton's plastic levers)

[Carlton green]

As an alternative you might consider measuring your drop out width and fitting an SA AW. The three speeds can, with careful overall gearing selection, take you all over the place - mine does and the simplicity is a joy. I can’t really argue against more gears being useful, but would merely say that a well chosen three can be enough.

The demise of Sram is a tragedy, they built some fine hub gears. I had one of Sram’s five speed hub gears and was delighted with it, it was the gear that SA should have built but instead SA somehow produced something nowhere near as good.

[Brucey]

FWIW it should be possible to use carefully chosen SA sprockets with a SRAM hub; the fitting is the same and SRAM's mods to the tooth shapes [to help shifting] are easily replicated by anyone with an angle grinder. It is also possible to fit two sprockets to an 'old' SA AW because of its longer driver.and this gives you even closer gears. BTW I think there are various workarounds for the NLA SRAM ball clips.

[hoogerbooger]

It is possible to use an old AW hub on a Brompton. Mine worked well and provided gears pretty similar to the SRAM ( slightly narrower range on the AW)
viewtopic.php?t=136334&hilit=Brompton+aw
(But it requires some fettling and it would not be cost effective to get a bike shop to do it.. .if you found one who was interested)

The Brompton BSR hub (IIRC) would give the same gear range as the old AW.....but I'm not sure the driver will take two sprockets.(??)

Brucey suggests that carefully selected SA sprockets can be used .....but when I last searched I couldn't find sprockets thin enough to get two on ( although I not saying I was exhaustive in my search). (I've been filing mine down to 3 spline from Brompton 9 spline sprockets)

It is possible to swap the driver on a BSR for the 9 spline version used on the BWR... so that you can then use Brompton sprockets without filing.....or from a dismantled cassette . SJS sell the 9 spline driver. But you have to be happy to get the spanners out to do the fitting

It may be sensible to see if you can test ride a 6 speed Brompton with a BWR hub.....to help you decide if gearing will work for you ....as this seems the simplest option.... .if you're likely yo do a reasonable mileage.

[rogerzilla]

^^ SRAM are still very much around - they just deleted the whole hub gear range in 2017, including spare parts. I understand they couldn't compete with Shimano and Sunrace SA, whose hub gears were sold more cheaply to bike builders.

[Brucey]

The Brompton BSR hub (IIRC) would give the same gear range as the old AW.....but I'm not sure the driver will take two sprockets.(??)

the BSR driver is short,like the current SA one, so it won't easily accept two sprockets. You may have to do some grinding in any event......

[in4time]

Have a chat with SJS cycles in Bridgwater. They sell lots of Bromptons and carry lots of spares for many bikes including Bromptons.

[Brucey]

IIRC it is also possible to use modified cassette cogs; just leave 3 of the original 9 splines but shorter so they'll fit an SA/SRAM driver. BTW a while back SJS were knocking out NOS AW hubs in 28h drilling for just £19.99 or something. A real 'rude not to' price in my book. If you are really lucky and your 13t sprocket comes from the 2nd smallest position, it may already have a helpful recess for the circlip

[drossall]

As above, if the hub is sound and has plenty of life left, a wheel rebuild should be almost trivially easy. Doesn't address issues such as supply of sprockets, obviously.

[Brucey]

further to my earlier post, you can buy suitable cassette sprockets [for modification] for about £10 a pair in 13-15t.

[hoogerbooger]

further to my earlier post, you can buy suitable cassette sprockets [for modification] for about £10 a pair in 13-15t.

(For the sake of completeness.....and as I needed to check for my spares box)
Photo of original Brompton SRAM 6 speed sprockets ( dark colour) and of the available Sturmey Archer sprockets (silver) below:

All are are 3/32" sprockets, but the original Brompton SRAM 13t and the currently available SA 15t and 13t have a built in spacer of 1 mm ( so take up 3mm in the stack). The original SRAM 15t is flat ( so 3/32" or 2mm) and is also shaped to aid gear change. (the used one shown is still a close match in profile to the last unused one in my spares box)

The original SRAM sprocket stack also has a 2.2mm spacer......so 3.2mm between sprockets. That means you will need a spacer of 1.2mm, or close to that, with the current sprockets.

I believe in previous threads rogerzilla or someone confirmed that the gears will change without shaping the standard 15t profile....but will change better if ground to the profile above.

( I doubt anyone will notice but the silver SA's above are actually 15t & 14t......but the 13t appears to be the same profile with the built in 1mm of spacing)

[Brucey]

a very few minute's work with an angle grinder would not only see that SA 15T reprofiled for better shifting but also 1mm thinner where it matters.