Note - this article was written 18 years ago and so some of the manufacturers have ceased trading - however the theory etc is all still up-to-date...
To the cycletourist reliability takes on greater importance than for all but the top racing cyclists. For example if a component on a racing cycle breaks - providing it's not dangerous, the result is at worst a lost race and a spoilt Sunday afternoon. For a tourist who may have only a couple of weeks a year on holiday, it can mean the loss of days, or perhaps the entire holiday. For the expedition tourer it can literally be a life and death event. Thus when picking the components for serious touring, reliability comes top of the priorities, far above weight or appearance. The common breakdowns on tour, spokes, cables and chain breakages can be sorted at the side of the road in a few minutes, but the next most common breakage - rear axle - is a major happening that may leave your loaded bike unrideable or even unpushable!
So what should you look for in a hub suitable for touring? Well first it must be a quick release axle. I know many will scoff at this "solids are stronger", but in my considerable experience of touring bikes this is simply not the case. But the primary reason for using quick release wheels was amply demonstrated this year when both I and my companion broke rear axles whilst cyclecamping in the Pyrenees. Mine was a Campagnolo Chorus, his a Specialized cartridge bearing model, both with screw on freewheels. The point is that neither of us know exactly when these breakages occurred, because we only found out after we had returned home and came to overhaul the bikes. In both cases the tensioned quick release had held the axles together well enough for us not to notice the breakage. Bolt on axles just break without warning and leave you stranded. In addition rear axles invariably break just inside the drive side bearing (more about this later), a crack caused by the upper half of the axle being in tension, propagating swiftly across the axle. A quick release applies a considerable compression load on an axle thereby reducing the stress at that weak point, and prolonging it's life. Here it's worth noting that it's not a one off load that breaks the axle, but the repeated application of a lesser load leading to a fatigue fracture.
So having decided on quick releases what next? Well I think a short explanation on the forces involved may help us decide. Basically an axle has a load applied at its ends though the dropouts, and is supported by its bearings. Where these bearings are placed is critical. Take a pencil and place it so one of its ends overhangs a table edge by about an inch. Now press down on both ends of the pencil. It will require considerable force to break it. Now move the pencil so it has half its length overhanging the table and repeat the experiment. The pencil breaks at the point where the support of the table ends. So logically the closer the supports (bearings) are to the load (dropouts) the stronger the axle.
Now imagine two men carrying a heavy iron girder between them. If they both stand at the extreme ends of the girder the load will be shared equally. Likewise if they stand next to each other at the centre they will again share the load. If on the other hand one stands at the end and the other in the middle, the latter will carry almost the entire load. Thus if a hub has two bearings and they are equidistant from the centre of the axle they will share the load equally, but if one is closer to the centre it will take a greater part of the load.
These two simple principles will help us decide what hub to use. However there is a little complication in that the drive side bearing takes more of the load produced when the rider pedals, though compared with the forces involved when the cycle hits a pothole, which may be many times the riders weight, this is relatively unimportant.
From the above it's easy to see the flaw in the traditional screw on freewheel type hub. Because the driveside bearing is placed inboard to make way for the freewheel it takes much of the load, and the axle beyond it is unsupported. Obviously the more gears you have on the freewheel the weaker the hub, what was adequate in the days of three speeds is clearly inadequate when faced with the length of unsupported axle needed by eight or nine...
So our touring hub must be a freehub, and the choice is generally between Campagnolo and Shimano. Campagnolo have taken the decision to place the drive side bearing well inboard of the dropout, thus leaving a relativly long piece of axle unsupported. They have addressed the problem of bearing load by using larger diameter bearings on the drive side, but that length of unsupported axle worries me. Axle quality does come into it and Campagnolo use good steel, but as I've already mentioned I've recently broken the axle on one of their screw on hubs and after only 15 weeks of loaded touring so Campagnolo is not for me - though to be fair Campagnolo cater exclusively for the racing cyclist. Shimano on the other hand place both their bearings at the ends of the hub, producing a much more evenly loaded design. To add to this our hire bikes use Deore LX and 105 hubs. They average 2000 miles a year of loaded touring each, have yet to break an axle or to have a bearing failure after three years of hire - over 100,000 miles between them. That is a spectacular reliability record, especially when you consider that hire bikes are habitually ridden over curbs, potholes and the like.
Both Campagnolo and Shimano use cup and cone bearings in their hubs, which over the last century have proved very reliable and easy to service. In the last two decades another sort of bearing has started to make inroads into this monopoly, and that is the cartridge or annular bearing more commonly found in cars and industrial machines. These bearings have been around for years but only recently has their use in cycle hubs become widespread. Their big advantage to the manufacturer is that the bearings come complete with races from the bearing manufacturer and can then just be pressed into a simple hub shell. This especially lends itself to small scale production as the manufacturer just has to produce the hub shell then fit industrial standard bearing "off the shelf". Cup and cone's need considerable tooling up to produce and are more complicated to assemble, if you are producing huge numbers of hubs then these costs get spread and the bearings themselves are cheaper, probably one reason why the big boys stick with them...
The two big manufacturers of cartridge bearing hubs are Sachs and Mavic. Sachs produce a hub with similar bearing placement to Shimano, one at each end, and which make a good alternative to XT. Which is better is open to debate, the bearings are larger in a cup and cone, and so stronger, but a cartridge bearing has twice the contact area for each ball - swings and roundabouts... For me the one big advantage of the Sachs hub for the tourist comes when the bearing starts to fail. Cup and cone's are adjustable, but if a bearing starts to break up miles from anywhere you continue to cycle at the risk of damaging the bearing surfaces inside the hub (cup) and on the axle (cone). When you reach civilisation the cones can be replaced if you can get the correct one, the cups in the hub can be replaced in a Campag hub, at a cost and if you can get them, but with Shimano it's a fiddle and you need to cannabalize onother hub... With the Sachs hub you just knock out the old cartridge bearings, it doesn't matter how damaged they are, then go to your friendly local bearing supplier, often a small machinery shop/moped sales/industrial machines supplier etc, and just press the new ones in - voila! a new hub. These industrial standard bearings are available anywhere in the world, even the third world uses small machines, so you'll never be stuck for spares, in fact it's worth carrying a couple in your tool kit.
Good though the Sachs hub, and other similar designs are, they miss one of the great advantages of cartridge bearings. In a cup and cone hub, the bearings work against each other and so are used in pairs. On the other hand there is no reason why a cartridge bearing hub should limit itself to two bearings, in theory the whole length of the axle could be packed with ten or more, though this overkill would result in a very heavy hub with a fair amount of drag! Mavic use a mix of ball race and needle roller bearings in their hubs, and many of the exotic mountainbike hubs have three or four. As long as they use standard bearing sizes these hubs are perfect for the serious touring cyclist, though generally at a cost.
One thing for sure, thanks to the evolution of the mountainbike the choice of strong, reliable hubs for touring is now better that ever.
See Breton Bikes new venture! For those wanting a place to drive their sportscar...!