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!

9 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?

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