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|
|Direct drive:||1st gear||5th gear|
|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!