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Choosing hubs for touring

THE HUB OF THE MATTER

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 lower 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 not with Shimano - exit one junk 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. 

My own bike is now graced with what I concider the best touring hub on the market,
and that's the DT Hugi mountainbike hubs. Made by the famous spoke manufacturer,
these sport four standard 6000 series industrial sized bearings. Two support the axle
within the forged hub shell, the other two support the axle within the freehub body
making a bomb proof hub. Having abandoned convention re bearings they have also
abandoned the ratchet and pawl freewheel mechanism used in every freewheel since
the year dot, and replaced it with a dog clutch using two toothed discs working over
each other. This is a much stronger system as broken pawls are not uncommon. The
clincher is that the whole thing can be disassembled and serviced without any tools, 
and makes the DT hub the one I would choose if I were to set off round the world
tomorrow. The one snag is the cost, and if funds were short I'd probably use a
Shimano or Sachs hub, perhaps  Deore XT, but the cheaper ones are pretty good and
have the advantage of building into a stronger wheel as they are 7-speed and so need
less wheel dish. One thing for sure, thanks to the evolution of the mountainbike the
choice of strong, reliable hubs for touring is now better that ever.