Kasai FS Hub Quick Release 6-Bolt Disc

The Kasai FS Hub Quick Release 6-Bolt Disc is a low-cost, field-repairable (to an extent) entry into the world of dynamo power. Coming in a range of axle types, spoke count, brake type options and colours, it's a good choice for the ultra-wilderness or the concerned rider.

Taiwan's Kasai has a good reputation for its Dynacoil hubs, but pretty much the whole range is factory sealed. That means if they stop working or need fresh bearings, it's a case of unlacing it from your wheel and sending it back to Kasai – rather a pain, to say the least. If you're in the middle of nowhere on a long bike tour, that could be game over for your trip.

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Dynamo hubs fail for multiple reasons, but the main one has to be immersion in water. When you're bikepacking that may be unavoidable or accidental, and dirty water and 'leccy don't mix. As anyone who's sunk a phone or spilt tea over a laptop knows, though, electric things can come back to life with a lot of drying, rice and airing cupboards... but these are in tragically short supply in many middles of nowhere.

In order to do that you need to get the hub apart, and that's where the FS – Field Serviceable – comes in. You do need to carry a 30mm spanner though, and obviously it's best to get a flat one designed for (thankfully still common) threaded headsets; regular 30mm spanners aren't exactly small or light. And make it a good quality one too, as although getting this hub apart is very simple, it's also done up very tight from the factory.

Just remember to unscrew the disc-side endcap first, or you'll be fighting the thread of the axle with likely destructive results.

With the 30mm nut gone, you're looking at the exposed coils of the dynamo – at which point you can clean/dry as required.

The FS hub comes in various flavours: either black or silver, disc or rim brake, QR or through-axle, and for 32 or 36 spokes. Note the through-axle version needs a 36mm spanner, as the axle is thicker (it takes 15mm axles, or 12mm with an adapter). You'll also need a dedicated 17mm driver tube tool and a hammer for removing the assembly.

Through-axle Boost forks (110mm spacing) require a £22.76 conversion kit to space the hub and disc rotor correctly.

Bearing gifts

The rotor-side bearing – a regular 6000RS bearing on the QR-axle version we have here – is easily replaced. You can't change the other bearing in the dynamo itself, though, as it's buried amongst the coils with electrical contacts passing through it. If this bearing fails it's a factory job, though it is at least less exposed to dirt and water than the disc-side one.

Alternatively, Kasai sells the whole dynamo assembly (bearing included) for £82. If a working dynamo is absolutely mission-critical, you could carry a spare at a relatively minor 340g.

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The FS hub is very easy to build a wheel around, as the spoke length is identical on either side, and there's a detailed and accurate tech document available. I built it into my bikepacking rig's 45mm-wide, 650b WTB Scraper rim with no hassles at all.

The plastic connector is easy to set up, and if you happen to rip the wires out – say a stick gets betwixt wheel and fork blade – the wires are easily stripped and reseated in the connector, with no solder required.

Kasai says the FS hub achieves 72% efficiency at 16kph/10mph, which is a good average for a bikepacking trip, I feel. At a nominal 6V/3W output, that makes for 2.16W. That gives you 0.36 amps into your AC-DC converter to give you USB charging – which, let's face it, is what most people want. Measuring current output with a digital USB charging dongle, I got pretty close to that figure.

I had the Kasai hub plugged into a €75 Cycle2Charge USB converter, which puts out 500-1000mAh between 12 and 21kph (7.5 and 13.1mph).

Bank charges

There's a lot going on here between the hub, the converter and the battery as speed varies, so the easiest thing to do is look at real-world results. Over a two-hour ride with a 10mph average (490m climbing over 36km) on my 3in 650B tyres, I got a useful 1000mAh charge into a battery bank. So over an 8-10hr day's ride at 10mph, you'll likely fill even a large bank for your evening phone/bike computer/fairy lights top-up.

Across other rides over the summer, the results pretty much tracked this 500mAh per hour average.

Of course on hillier terrain it'll do less well, as you'll barely be charging at all slogging up long hills at three or four miles per hour with a pack full of spanners and hammers, and the boost you get down the other side is over too soon unless you're dragging your brakes to maximise it. Overall, the Kasai FS hub does the job though, and I was never left in the literal or figurative dark during trips into the wild.

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Opening up the hub after a few good, prolonged dunkings fording calf-deep burns, I found no moisture inside. That's not to say it's 100 per cent watertight – rather, there was no trace a few days later. I imagine the hub warms somewhat over time, helping to evaporate and drive out moisture.

Value

I'm not aware of any other 'field-serviceable' dynamo hubs on the market, so at £155 the Kasai FS is in a class of its own. You can buy non-serviceable QR dynamo hubs from the likes of Panasonic for around £80, whilst an industry-leading SON hub will set you back around £250.

At 480g it's heavy, but only 40g heavier than the non-repairable SON 28.

Overall

Though one of the two bearings is still inaccessible, the ability to otherwise maintain and repair this without having to unlace it from your wheel, parcel it up and send it off is potentially very valuable. In fact, it's unique among such hubs. And if you are really pushing the zombie apocalypse vibe, carrying your own spare coil assembly is the ultimate solution.

For £155, Kasai has created a great option for keeping you churning out the amps.

Verdict

Owner-serviceable and great for remote trips or long-term, low-cost dynamo hub ownership