Two of the most popular hubs for a Brompton 8-speed conversion are the Sturmey Archer x-rf8(w), and Shimano’s Alfine SG-S501. There are pros and cons of both. If you’re looking to do your own 8-speed conversion, which to choose? Below is a summary comparison table.

Sturmey Archer x-rf8(w) Shimano SG-S501
 Price: Around £150 Around £150
 Internals: Ratchet (noisy) Silent
 Direct drive: 1st gear 5th gear
 Gear range: 325% 307%
 Over-locknut width:  120mm 135mm
 Needs frame widening:  No  Yes
 Gear changer: Gripshift or lever Triggers
 Spoke hole options: 28, 32, 36 32, 36
 Needs extended chain tensioner: Yes No

 

On the face of it, the Shimano hub is simply a better product. For a similar price to the Sturmey Archer, you get a quiet, reliable hub, whose gear changer always delivers a secure change. I have ridden my ‘big’ bike for 7 years with the Shimano hub. It has only failed me once – at minus 5 degrees C when the internals froze, and I had to beg a cup of boiling water from Costa to pour over it. By contrast, the sound of the Sturmey Archer (SA) has been likened to a swarm of angry bees, especially in gears 4 and 6. I don’t need to look at the Sturmey gripshifter to tell me what gear I’m in – I can hear it! The gripshifter itself can land you between gears, especially if you turn it by mistake when needing to hold on tight – although there is a new lever control available.

But when it comes to choosing a hub for a Brompton 8-speed conversion, the decision is not so clear cut. There’s lots to like about the SA hub. Its direct drive gear is gear 1, which means your steep hill gear is also your most efficient. In a hilly city like Edinburgh where I live, it’s very useful. It also makes sense if you want to tour on your Brompton, carrying weight. Related to this is the fact that the gears are not spaced evenly on the SA – most gears differ by 14%, but the top and bottom gears differ from their neighbours by 30%. Dropping from 2nd into 1st gives you real comfort on the steep hills, with this ‘granny’ gear. What’s more, the SA offers a top to bottom range of 325% compared to the Shimano’s 307%. This means you can afford to gear the hub for low comfort, but still reach reasonable top speeds under power.

Another benefit of the SA comes when you try to fit it. By removing one of the double lock-nuts, you can drop the overlock-nut dimension of 120mm to just 116mm, which is within 4mm of the 112mm gap between the rear triangle’s dropouts. In other words, the SA hub can be fitted with a bit of stretching, without needing to permanently widen the rear forks. Apart from avoiding this task, not tampering with the forks means the bike will fold better; and in the fold, you won’t face issues of the chainwheel fouling the widened fork frame, which would necessitate a longer bottom bracket. Further, on the narrower hub the short spokes will be at less of an angle to the rim, allowing easier tensioning. In short, the SA hub can be fitted fairly easily, without ‘shoe-horning’ it into place. An added advantage is that it comes with a 28-hole version – so you can re-use your existing Brompton rim if you want to.

One last area to think about is the tricky chain tensioner. Here’s where the Shimano edges ahead once more. The smallest sprocket the SA can take is a 20T. This means that the tensioner’s arms need to be extended, to avoid the jockey wheels fouling the sprocket. Various options are possible – the very neat job done by Tiller Cycles pictured here is one such solution. (I’m not sure he still does these.) However you do it, it’s a problem to be solved. By contrast, I have discovered a way round this problem on the Shimano hub: fit a 16T sprocket (54T chainwheel) dished outwards. (Shimano lists this as a valid option.) Then use the slightly longer chain tensioner intended for 2-speed bikes, and cut its rear face flat with a hacksaw. 1-speed jockey wheels can then be mounted against the ends of the tensioner’s cylinders, and the spacing works perfectly to align the sprocket with the jockey wheels. There are some other tricks to make this work – I’ll detail it in another post. The simple point here is that that one big advantage of fitting the Shimano hub is you can do so without needing extensions on your chain tensioner. Result!

What about gearing – i.e. setting the range higher or lower? There is too much to cover here, but the headline is that the SA gives you more options than the Shimano setup described above. Perhaps that’s for another post. In all, the choice between the two hubs will come down to individual preferences – what you can live with – and what you can’t live without!

15 Comments

  • Robert

    Hello,
    Thanks a lot for very interesting article.
    I wander about installation in my old Brompton (M3R) – an Sturmey Archer X-RF8 hub. I don’t want to modify or change rear tringle – so this is only option. After raeding your description of modification I started looking for parts for it. Specially i was looking for modified tensioner. I found this web page:

    http://www.brommieplus.com/portal_c1_cnt_page.php?owner_num=c1_343119&button_num=c1&folder_id=44131&cnt_id=339010

    There is also an description of installation and offer of all necessary parts. This site mentions one more requires change that is not described on your blog – chainring/chainset replacement. Is this really necessary? Have you made such change in your Brompton?

    Greetings.

    Robert

  • dunxmac

    Hi Robert,

    Thanks for drawing to my attention the brommieplus website – I hadn’t seen this before. That looks like a good solution. In the past I’ve modified the tensioner meant for the 2-speed derailleur type Brompton gear, in the way they suggest, in situations where I’ve needed the longer arms of that tensioner. It’s a good work-around.

    You ask about chainring replacement – yes, I’m afraid you do need a smaller chainring to get a reasonable spread of gears, unless you’re very strong. I use a (very cheap!) shimano 33t (with a 23t on the rear) which has raised a few eyebrows in bike shops, but it gets you up steep hills with ease (about 1.89m forward per pedal revolution, from memory), especially since the Sturmey 8 speed is in direct drive in 1st gear. Example here: https://www.sjscycles.co.uk/chainsets/33-shimano-nexus-fcc6000-single-chainset-silver-170-mm/

    You can play around with the Brompton Gear calculator (http://xldev.co.uk/bgc.html) to see what chainwheel would work best with a 20t at the rear. Using just the lowest Brompton chainring at 44t would ‘lose’ you your bottom two gears.

    The other factor is whether you change the bottom bracket while you’re at it. I think newer Bromptons are a 119mm BB – I can’t remember what I put on mine, but I shortened it to bring the chainwheel towards the frame and reduce the angle of the chainline. However, don’t forget the fold here – the chainwheel still has to clear the rear triangle in the fold – I’ve found leaving a 4mm gap sufficient. Remember to calculate for the width of the chain as well, as the chain seated on the wheel is what in practice has to clear the folded frame.

    Good luck with it!

  • Tom Taylor

    I plan to convert my 3 speed to 8 with the Sturmey Archer hub. I’m about to build the wheel and need to decide whether to remove that second locknut before I can measure up and choose the correct spokes. Can you let me know what issues I might face by removing the nut? Is it safe to remove? Will it make the cold setting easier? Will it make the fold easier?
    Many thanks for helping out.

    • dunxmac

      Hi,

      Thanks for the question. So far as I’m aware there are no safety issues with removing the second locknut. It was an experienced mechanic that drew my attention to this option. One locknut should be enough – it’s been good enough on every set of (non-cartridge) bearings I’ve ever ridden. And yes, it will make getting the wheel in easier. The over-locknut dimension (OLD) of the Sturmey 8 with two locknuts is 120mm. The Brompton rear dropouts are around 112mm. A locknut takes up 4mm. So by removing one, you reduce the OLD of the hub to 116mm, just 4mm wider than the dropouts. This means you can ease the wheel into place with just thumb pressure on the hub, whilst pulling the frame away from the hub with your fingers.
      And yes, it will also make the fold easier, because widening the frame (e.g. for the Shimano Alfine 8) can cause problems if you have a large chainwheel, like the 54T, because the teeth collide with the rear triangle in the fold. You can get round this with a longer bottom bracket, but this may cause chainline issues. (TBH, I haven’t actually solved the chainline issue for the arrangement – others may have – so I have to be careful not to back pedal!) The other issue with the forced widening of the rear forks is that the nearside pedal crank can foul the rear triangle in the fold, depending on the design of your crank. On my Alfine 8 Brompton, the crank just passes the triangle and no more, scuffing a bit of paint in the process. It’s not a disaster if you can’t turn the pedals the whole way in the fold – you just have to arrange your pedals prior to folding, so that the RH pedal is places to tuck up against the wheel. But back to the Sturmey 8…
      So it sounds like you’re good to go. The Sturmey 8 is a simple solution if you don’t want to faff around bending the frame. The downside is you need to find a way to extend the chain tensioner, to clear the larger rear sprocket that the Sturmey takes. Good luck with the job!

      • Tom Taylor

        Hi, thanks for the help. I made the wheel with standard 2 cross pattern but when I try it in the frame, the outbound spokes on the non drive side foul on the stay and the wheel won’t go around (!) There are a few options I can think of—shim the axle with some washers to force the dropouts apart; remake the wheel with all the non drive side spokes inbound; find a metal badger to modify the frame. I think the best of those is to remake the wheel, but I wondered if anyone had a similar experience and better advice?
        Many thanks, Tom

        • Duncan

          Hi, I was advised not to cross the spokes on the non-drive side (I realise this makes your spokes the wrong length), but if you can have the spokes crossed and all inbound, that sounds like a good solution.

          • Tom Taylor

            Thanks Duncan. I’ve remade the wheel with the same spokes and it looks ok (fingers crossed). Does anyone know what is the maximum size chainring I can use with the XRF8/20t hub? I think something like a 44t ring would give me the hearing I need, but don’t know if it would foul in the fold?

  • Martin

    I’m using an 8 gear Shimano Nexus (not Alfine) with gripshift on Brompton since many, many years.
    It’s great, but the widening of the rear part is problematic.
    The Nexus broke once and I had to replace it.

    Now I chose the Sturmey Archer for my other Brompton, again with a gripshift.
    Switching gears is not as smooth as with the Nexus, and the noise is frightening.

    However, I like the Sturmey Archers transmission ratios better than the Nexus.
    In the highest one, it’s like flying.
    Also, I prefer it for the fact, that it does not need the widening of the Bromptons rear part,
    which can be dangerous.

    One thing does not work yet with my Sturmey Archer: The fourth gear does not work at all, it’s idle.
    I assume, that it is not well-adjusted, but I’m not sure, what exactly is wrong.

    Any ideas? Thank you in advance!

    • Dave

      I have an SA 8 speed in my Brompton and fourth gear is the one that shows up poor adjustment. When I initially fitted the 8 speed and adjusted in fourth so the yellow paint mark was central in the window fourth gear would not engage. I’ve found that on my particular hub the cable need to be slightly tighter so the yellow is half obscured and everything then works as it should. On the issue of noise from the hub; the hub is reasonably quiet if the adjustment is spot on, what I mean by this is that you can adjust the cable so all the gears engage correctly but the hub is very noisy. I have found that as little as half a turn on the cable adjuster can be all it takes to get the hub as quiet as it will go.
      Dave

  • At the time I was making a similar decision the SA 8 speed was new to the market as was the Alfine 11 and hence reliability for both hubs was an unknown factor. This was in contrast to the Nexus 8 hubs which I discovered were being (ab)used well outside recommended chainwheel/sprocket ratios in the mountain biking community without problems. So I chose the Nexus 8 hubs for my conversions.

    https://mistymornings.net/blogs/mm/?p=123

    I must dig out my Brompton this spring and start using it again.

  • Gilles

    Thanks much for the article.

    I built a Nexus 8 wheel with a 16T cog — the smallest from Shimano, and happens to be dished —, and am about to ask a seasoned bicycle frame maker to cold set the triangle to fit it into my Brompton.

    After reading the article + comments, I’m concerned, though, that it will impact the fold and the chainline, and the chairing might rub against the nearside stay, especially since I’m using a a double crankset for wider gear range in really steep climbs.

    Before going ahead, any advice I should give the shop, who isn’t used to working with Bromptons?

    Thank you.

  • dunxmac

    Hi, This is certainly one to watch out for. The larger the chainring, the further back it will protrude in the fold, and the greater chance of striking the rear triangle stay, especially if widened to fit the Nexus 8. Ways round are to have smaller chainring (but this lowers your gears overall) or to compensate by fitting a wider bottom bracket. The disadvantage of the latter is you are more likely to compromise the chain line. I have made this work happily with both a 39t chainring and the biggest Brompton 54t ring. The 54t did foul the stay with the standard (?119mm) Brompton BB. I can’t remember what I increased it to, but a few mm did the trick without harming the chain line too much. When you think what a chain tolerates on, say, a 10-speed cassette, a bit of an angle is not disastrous. The main issue I have found is the chain coming off the rear sprocket when back-pedalling quickly – I just learned not to!

    I’ve found some old notes in a file that suggest that with the rear sprocket dished out, the chain line is 47.7mm on the Alfine 8 (OLD=135mm). I worked out a 122mm BB would give a chain line of 48mm, which was nearly spot on, and brought your chainwheel away from the stay. (Don’t rely on these numbers, my notes could be wrong!). The other variable is the design of your chainring/cranks – different cranks may site the chainring further left/right in relation to the square taper hole. I can’t comment on double rings at the front, though I wonder whether the extra width would prevent the hook on the front wheel reaching the stay and clipping over it in the fold?
    Good luck with it and hopefully a bit of tweaking will get you what you need.

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