Let me begin with a warning: this is not a product I'd recommend to every rider for every bike. It has worked reliably on my folder for years, but I don't put more than 69 Nm into it (rider weight 70 kg, crank length 170 mm, chain transmission 42/25). My colleague Jura, who cranks something over 100 Nm (chain 28/25, the rest assumed to be the same), has had two tooth failures already. I've found several reports of similar failures on the net. Helios (Czech bike parts dealer) decided to stop selling these hubs because they return quite often. That means: the hub is suitable for smaller loads only (small wheel and overdrive chain transmission), not for anything else (standard-sized wheel and chain about 1/1).
Tactical data: eight gears, total range of 325 % (a bit more than 8-speeds by Shimano or SRAM). Gear 1 is direct drive, all others are overdrives. Weight of almost 2 kg. There is also a drum brake version X-RD8 and brakeless X-RF8.
The shifting is quick and troublefree as long as you don't push on the pedals during the shift. Six middle gears are evenly and quite tightly spaced (I often shift by two at a time), the first and last are further apart. Pulling the cable shifts to slower gears, releasing it to faster, as usual. The hub is quite noisy, especially gear 4 whirrs like an electric motor. Until the control cable beds in, you have to check the adjustment periodically; the tolerance is quite narrow and hitting an intermediate position is asking for trouble. Cable tension is adjusted by a screw on the shifter and checked by a yellow square under a slot in the cable drum (the yellow is not very visible, so I repainted it red - see photo above). It's good to start with the adjusting barrel screwed all the way in, so it can take up the slack developing in the cable.
Statically unbalanced shifting pawls sometimes randomly engage faster gears if the wheel bounces hard (even though it shouldn't be possible, given the cam design). You can always reset the gears by a quick backpedal, but when trundling uphill at gear 1, it probably makes you get off and push. Cobblestones are OK though. I retract this and apologise for the wrong conclusion! The problem was caused by inappropriate cable routing: stops on both sides of a folding hinge with enough play to move them and the cable on every hard bump. The hub has nothing to do with it. After removing the stops and installing a full-length outer cable, shifting feels lighter and is absolutely reliable.
Shifting grip or thumb lever, cable and all nuts and fittings are included in the package. It is possible to lace the big hub into a 20" wheel with 36 spokes and standard triple crossing, but the spokes slope a bit too much, double crossing would be better. I don't recommend any bigger wheels.
The rotary gear selector is completely hidden behind the dropouts, so it's shielded from damage. Cable stop can be attached in two possible positions for horizontal or sloped dropouts, so the cable hides neatly behind the chainstay. It is not necessary for the function though, so if you for example have small rear fork with steeply converging chainstays, you can let the cable stick out up or down to clear them. Possible problems are the cable stop rubbing on outward-dished sprocket, and anti-rotation washer tabs being thicker than the dropouts. Both are easily fixed with a file.
You only have to adjust cable position once. When unmounting the wheel, you just unhook it and then put it back without further adjusting.
More or less the only thing which needs periodic inspections or replacement is the control cable: it passes through a rather sharp bend in the shifter and cracks over time (see picture, it took 12000 km to get to this condition). The sprocket will also wear off one day, but given the width and tooth count, its life span should be in the order of tens of thousands kilometres (spares are available and inexpensive). The internals are well adjusted and greased by the factory, so just install and ride. I recommend to repack every two years or 6000 km - three years are too much, planet cages start to squeal and drag on the axis by then; on the other hand, one year is unnecessarily frequent. The manufacturer recommends any major overhauls to be done by "authorized dealers who are equipped to carry this out" and gives us amateur tinkerers just one drawing and a part list. Fortunately, the mechanism is not very complex, so we can do our tinkering even without a manual - see below.
Hub shell is made of polished aluminium, cable drum on the right side is plastic, everything else is galvanized steel (I can't see if the cogs run on any bushings). Weather protection is done by labyrinth dustcaps, so riding axle-deep in water is not a good idea. But normal rain, dust and mud are kept out very well, as proved by perfectly clean grease I found in the bearings every time. And the bearings are of good quality, they still look like new after eight years of daily use.
Hub with a (W) in its name is a second generation. The first one had a separate gear and ratchet ring on each stage (see example here). Now there is just the gear ring which doubles as a ratchet. Saved space and material was probably used to reinforce everything that was left, but it's not enough yet. This happened to Jura:
First failure (leftmost picture) was two broken teeth on the gear ring of last stage (the part which also contains main freewheel). It happened in normal use during a stronger push on the pedals, after about 500 km of use. There's a planet-cog-shaped hole in one of the teeth, so I guess it was a local material flaw - the tooth was softer than it should have been. The other tooth might have been broken off by a fragment of the first tooth, but it's just a guess.
Second failure (middle picture) happened a year later: one of the three ratchet teeth on first stage broke off. First breakdown was covered by warranty, dealer delivered a new ring and complete previous stage. The second one wasn't, but the dealer (already mentioned Helios) sent a new hub anyway.
My hub still has all teeth intact, but a lockwasher on the right end of the axle has cracked apart after about 6000 km of use. It is cast of some rather brittle metal (cast iron?) and has little bumps along the perimeter to bite into aluminium dropouts and help keep the axle in place. But my dropouts are made of steel, so stress peaks and more shear loads developed, eventually destroying the washer. The event was quick: after the washer cracked, right axle end moved forward and chain fell off. So I stopped on a sidewalk and found what happened and how lucky I was - had it happened half a mile sooner in a steep downhill before a crossroad, maybe I wouldn't be writing this now. Quick solution: fabricate a new washer out of sturdy steel (see last two pictures). Lesson learnt: NO MORE cast washers.
The gearing consists of three epicyclic stages connected in series, each with a different gear ratio. Driving torque is input on the planet cage and output on the outer gear ring. Sun gear is either locked with the axle and the stage works in overdrive mode, or it spins freely, the gears lock by the integrated ratchet and work in direct drive. Each stage is controlled independently by a rotary cam and a pawl sticking out from the axle. Three stages by two positions give the resulting eight gears. The best efficiency (the least cogs engaged) occurs in the low gears - good for quick starts and hill climbing, not so good for high speed cruising.
| gear | C | B | A |
|---|---|---|---|
| 1 | 0 | 0 | 0 |
| 2 | 0 | 1 | 0 |
| 3 | 0 | 0 | 1 |
| 4 | 1 | 0 | 0 |
| 5 | 0 | 1 | 1 |
| 6 | 1 | 1 | 0 |
| 7 | 1 | 0 | 1 |
| 8 | 1 | 1 | 1 |
The cams are marked A, B and C. Each of them controls one epicyclic stage according to the table on the left. 1 means engaged pawl, locked sun gear and overdrive mode; 0 means retracted pawl and the sun gear free in direct drive. The pawls engage via springs and get pushed back by cams. Engagement is theoretically possible under full load (a pawl pops up and waits for the sun gear splines to meet it), retracting works only if no torque is present. That means shifting from 1 to 2 and from 7 to 8 works under load, all other transitions do not. Not really worth remembering, better to always ease off before shifting.
Note: if it works, don't mess with it. If it doesn't, something has probably cracked apart and you can't fix it anyway. If you just need to pour water out, replenish grease or remove cracked bits and limp to nearest bike shop, keep reading. There are no traps (except the cam mechanism which usually doesn't have to be disassembled), all threads are right handed and all you need is a flat 16 mm spanner, two 17s, C-clip pliers and a vise.
First remove the sprocket and dustcap on the right side, then the cone on the left side and then the big notched gray ring on the right (it requires either a special wrench, a vise, or tangential tapping into the notches). After that, the internals fall out in one solid bulk:
If you remove a C-clip on the left side, you can pull the output ratchet and all three gear stages off the axle. If the control pawls don't let them go, shift to gear 1 to retract them.
The hub comes from the factory well greased: yellow grease for the bearings, black graphite goo for the cogs. Be very careful to keep dirt away from the gears - the stages are riveted and can't be taken apart for cleaning; all you can do is to add grease.
I really don't recommend to disassemble the cam mechanism, there's nothing interesting inside and it's tricky to put back together correctly (most parts fit in multiple positions and only one of them is correct).
OK, you were warned. All you need is to unscrew the nut on the right end of the axle and to pull out everything you find under it. Look out for one pre-tensioned spring and other traps. It's a good idea to take photos of the process so as to have some reference for reassembly. By the way: the cams go back in A, B, C order; if you mix them up, they won't shift. Cable drum is best to leave completely dry or only lubricate near the centre - grease thickens in winter and can make upshifting slow and unreliable.
As you can see, I've already been through the complete stripdown. The main reason was curiosity, the excuse was a new noise that sounded like something loose lightly rubbing on something spinning. The hub started to emit it in gears 4..8 after 2100 km of use. It was probably caused by the planet cages - they slide on each other and if the grease creeps out from between them, you start to hear it. I've found no mechanical failures, all moving parts were in good condition, ball races shiny like new and the grease perfectly clean.
I did last stripdown (so far) when the speedo showed 19392 kilometres, three years after previous one. It was long overdue, last gear ring with output ratchet was dragging on the axis so much that it was like riding with a brake applied, and it took several backpedals to find a usable position. The drag is probably caused by slight nonconcentricity of output ratchet or its pawls. It makes the gear ring body cross, lean onto the axis by its middle hole and onto previous planet cage with its gear teeth. It even made dents in it, as you can see here on the third picture:
I solved it by proper regreasing. The drag is harmless, the worst that can happen is the touching surfaces grind away enough to stop dragging. All other parts look OK, polished spots on axis and shifting pawls didn't grow significantly since last time (feel free to compare the photos), the cogs still have all teeth intact.
The sprocket shows signs of wear, but nothing fatal, it still works:
X-Rsomething8 is a good choice for folders and similar small-wheeled machines which would otherwise require huge chainrings or tiny sprockets. Good efficiency of low gears works well for hills and stoplights; the high end is only used downhill and there are speed limits in towns anyway.
The hub is not suitable for standard-sized wheels where it can't be trusted to survive all the torques.
Durability? Over 20000 km so far on my folder, still alive and well. If you have any more experience (mileage, failures etc.), feel free to share.