Originally Posted by
Kimmo
Well, I dunno about lighter; It's not just the smaller splines necessitating steel or titanium; the ratchet has to fit inside a 12t, so it pretty much has to be the same bit of metal forming the splines, and I'd bet the inner section of Dura-Ace cassette bodies is steel... and what with oversize axles first, and now disc hubs, there's even less room. Hence Shimano's relatively few points of engagement, the only real Achilles heel of the design.
Come to think of it, I've wondered in the past if it'd be possible to take Shimano's arrangement and move the ratchet inside the hub flange... that'd leave you with a C-shaped load path between spokes and bearings though, unless you could get it really compact...
Damn ratchets! I want a nanotech solution.
Yes, that is a constraint of the Shimano freehub system: that the ratchet mechanism has to fit inside a freehub body that takes a 12-tooth cog. One could make a stepped-diameter system in which the larger cogs fit on a larger diameter spline, the way Shimano and Sachs and freewheels were constructed. Then the ratchet mechanism would sit inside the larger diameter body. Still, there are millions and millions of Shimano freehub-based (and clones) systems on the road, and failures in the freehubs are very rare. I don't see the small diameter of the ratchet mechanism to be a problem in practice. The only failures I've seen are on bikes that were ridden a gazillion miles in wet dirty conditions, and the freehub simply got filled with crap and seized up. But at our local Co-op, we have a heavy bucket 'o freehubs for $5 each, so the lifespan of your Shimano rear hub should be infinite.
I have taken apart XTR and Dura-Ace titanium freehub bodies down to the little balls - yes, the guts of these are steel. Only the freehub shells are Ti.
As far as points of engagement, I am not fussed by Shimano's 20 or so points. I've ridden on clutch systems in which torque engagement is instantaneous, and I did not see any detectible improvement in my performance or 'ride experience'. I know that some of the small-fry hub vendors like to boast of an increased number of engagement points, but this reminds of the food processor wars of of the 70's, where blenders had to go from 3 speeds to 11 or whatever, in a game of pointless manufacturer one-upmanship. Same issue with the number of pawls in a hub: the small fry manufacturers boast of 3 or 6 or whatever number of pawls, as if it is some kind of arms race. Since only one pawl can transfer pedaling torque at any time, increasing the number of pawls does not increase the 'strength' or power transfer of the hub.
Something to ponder: because the bearings on Shimano hubs are loaded at the ends, the optimum design, this allows a thin axle to be used. On the Campy-style hubs, the axle has to be bigger in order to compensate for more unsupported/cantilevered load. So why should Shimano be required to increase the diameter of their axles, thereby consuming precious space inside the hub?