^ Yeah, I agree.
Zipp's counter to that is the following, but I don't buy it; well, I don't buy all of it. To be fair, it's a pretty old article. Are the cartridges they use deeper-grooved than regular?
I suppose one obvious comment to make is that there have been a billion pros winning races on these hubs at a billion mph for many years, so they can't be all that bad.
But that's got nothing to do with maintenance and reliability.
------------------------------Radial Contact instead of Angular Contact
One area that we feel strongly about with our hub design, that is not shared by any other manufacturers in using
radial contact bearings with ideal ball location. This means that we utilize deep groove cartridges, but confine
their location to be optimal for friction and life, and do not allow them to be preloaded or adjusted by the
consumer. Why are we so adamant about this design? And what does that mean for you, the consumer?
First, radial contact bearings much better handle the loads seen in a bicycle hub, and nearly ½ the manufacturers
out there are using them. The radial ball loading better distributes the load fed into the hub, and can handle
higher loading using lighter weight bearings that generally spin smoother than cup and cone type setups.
Granted, that cup and cone bearings can be carefully adjusted to feel near perfect in your hands, but once the
wheel is on the bike, the loading of the cup and cone bearing actually results in higher ball friction and reduced life.
The key to notice in the Radial vs the Cup and Cone design is that the force Fn is the Normal (vertical) force fed
to the bearing through the weight of the rider. In the radial bearing design, Fn is the same force resisted by the
ball, but in the angular contact situation, the normal force is only one component of the ball force, since the ball
contact line runs 45 degrees to the force line, the ball must generate √2 times more force (and a lateral force
component represented by FL). This means that Factual is 1.41 times greater than Fn, so the ball in the cup and
cone scenario sees 41% higher load than the radial ball bearing. This higher ball load results in higher friction,
decreased ball and race life, and increased wear of the internal components meaning that the hub will have to be
adjusted more frequently.
The reason for the cup and cone design is quite simple, it is much less expensive to machine and assemble since
the components are adjusted for preload by the consumer. This means that the bearing race diameters can have
nearly twice the tolerance, and there is little to no need to axial tolerances in the assembly as any slop can be
accounted for in the adjustment of the cone. Contrarily, the radial ball situation, requires exact dimensional
control of both bearing bore diameter, as well as axial length of both hubshell and center spacer, as well as
requiring bearing planes to be exactly coplanar to each other. One design variant now becoming popular is to
utilize radial cartridge bearings but to use an adjustable cone design, allowing for user adjustability for bearing
preload, but this essentially negates the gains to be had in using radial cartridge bearings (other than the better
seals). The precision necessary for a perfect radial cartridge hub is on the order of +/- 0.0002” in 3 axes, this is
simply unachievable in Asian production, and is not even achievable in most types of CNC equipment, so it is
very, very expensive to obtain. However, with proper machines and fixuturing, the Zipp hub is manufactured to
these exacting tolerances and specifications, the only hub in the world to do so. The result is a hub that spins
with as much as 1 watt efficiency improvement over competing designs! What’s 1 watt mean? Well, that’s
roughly 2-3 seconds in a 40k time trial, and it was all achieved through design and process control measures. http://www.zipp.com/_media/pdfs/technology/hubs.pdf