Like single speed but need gears?

They’ve been making things for quite a while.

One product that’s received a makeover is the Duomatic 2 speed hub, it’s been around in one guise or another for years but a 120mm OLD and no disc capability left it languishing well below most peoples radar. In practice the Duomatic has 2 gear ratios, the first is a direct drive, so just like a single speed and the second produces a 38% overdrive. There’s no shifter or cable, a quick kick-back on the pedals is all that’s required to shift from one ratio to the other … cunning?

If that sounds like a good idea but you wished it was available to fit your mountain bike, then you might be glad to know that someone at Sturmey Archer had the same idea and produced the Duomatic S2K … 135mm OLD? – yep, 6 bolt disc mount? – present and correct , aluminium hub body in a range of anodised colours to match your handbag? – depends on the handbag.

20,21 and 22 teeth guess which we picked.

The S2K will fit any mountain bike, obviously a single speed(able) frame is ideal otherwise you’ll require a chain tensioner but anything with 135mm spaced drop-outs and disc brakes is a potential candidate. The hub uses the same sprockets as other SA hubs and the same 3 spline and circlip fitting arrangement. Sprockets are available in sizes 13t up to 22t, either flat or dished to fit both 1/8″ or 3/32″ chains … at £2.99 each there’s no excuse for not having a few around to try. The hub features a nutted axle and comes supplied with the corresponding nuts and anti-turn washers, just make sure you fit them.

Tool free changes, 3 splines and a circlip.

The first sprocket I tried was an 18t mated up to a 32t ring. A quick blast down the lane followed by a slow tootle back, lead me to seek out a more forgiving ratio … a rummage round the workshop revealed  20, 21 and 22 toothed sprockets. The 22t seemed like complete overkill until I thought about the overdrive gear. If I used the 22t allied to a 32t up front, I’d have a direct drive  ratio of 1.45:1 which means easy climbs ahead … if you fitted that ratio to a single speed, it would also mean spinning like crazy on anything that even hinted at going downhill. However, if I ‘change gear’ in the hub, the same 32 x 22 would produce something that feels similar to a 2:1 ratio or 32 x 16 in single speed speak … which is more than enough for the flat bits on a 29er.

Given that the hub is adapted, rather than designed for mountain bike use my only concern at the moment is hub sealing … never a strong point on SA hubs but never much of an issue either. Allowing for the fact that the hubs are easy to work on and spares are readily available and cheap, hopefully any ingress of too much liquid sunshine will be easily remedied.

The video below hopefully demonstrates how you change gear more clearly than words.

While the hub’s internals are common to other SA models (so easily sourced), sadly the same can’t be said of the SK2 hub itself. I couldn’t find one in the UK when I first discovered them, so I contacted the importers … they’d never heard of it and thought I might have imagined a 135mm Duomatic with disc mount. I assured them I hadn’t and intrigued they went off to contact the SA European head office. Oddly, they too were unaware of the existence of such an item and so had no intention to distribute it amongst the weary cyclists of Europe. So, if you’d like one you’ll have to visit the world wide web in the US and buy one directly – expect to pay around $90 (£56).

I’ll be back to let you know how it’s coping with the onset of Welsh Winter.