Wednesday, July 20, 2016

Shimano Dura-Ace 8S hubs

If these hubs aren't the greatest hubs ever produced...forget that....this design *is* the greatest hub design ever.   These are the original Dura-Ace 8s "freehub" design that came with the first-gen Dura-Ace 8-speed Shimano Total Integration ("STI') shifters.  These hubs came in "UniGlide" and "HyperGlide" styles.  I don't have pictures to illustrate the difference, but they are minor, compared to the revolutionary axle design of this hub.  Since the introduction of this design, Shimano has never varied from the design elements that make this design so important.   Modern 11s Dura-Ace hubs employ this same design.  They may have updated the materials and/or made the hubs lighter, but the "free hub" is still there.



What makes these hubs so cool (and so revolutionary) is the placement of the traditional cup-and-cone bearings.  Prior to modern free hub designs, the individual cogs (the gears that contact the chain and drive the bike forward) were connected to a "freewheel" that had its own, separately removable ratchet mechanism.  The freewheel (as a free-standing whole of cogs and ratchet bearings) would then thread onto the aluminum hub via large threads that mated the steel freewheel threads to the aluminum body.  Not only was that problematic (soft aluminum and hard steel do NOT like one another), the design had major flaws.  The inherent disadvantage of the freewheel design is that it meant the axle bearings had to be located where the aluminum hub body ended, with a long section of axle left over to extend *through* the freewheel body before the axle hit the dropout on the bicycle frame.  This created (creates) a huge leverage point where rear axles break under stress.

Moving the cup-and-cone to the ends of the axle GREATLY reduce broken and/or bent axles and also made changing cogs much easier.

In the above picture you can see the first freehub design.  On the left is the free hub itself (removed from its aluminum hub for servicing) and on the right is a separate free hub secured to the hub, ready to have the axle re-installed.  If you look closely at the aluminum body on the right, you can see the bulge in the hub body that houses the securing-screw on the freehub (the threaded extension on the left part.)



This picture shows the outboard side of the free hub itself.  You can clearly see the bearing-race on both free hubs.  Notice that the bearing races are on the OUTBOARD SIDE of the freehub design.



This picture shows two things:  1.  How the threaded extension on the freehub body screws into the aluminum hub, and 2, that the aluminum hub has no bearing races.  The large threads secure the freehub to the hub.  With the bearing races on the outboard side of the freehub, it effectively moves the bearings a full inch (or more) towards the end of the axle - as demonstrated in the next picture:



Here you can clearly see the complete hub/freehub and the axle I just removed from it.  Notice that the bearing cones on the axle are as fully-outboard as possible for the axle.  The bearing placement removes a huge weakness for standard axles.  Each of my two pair of Dura-Ace 8s freehubs have *at least* 20,000 miles each and are well over 24 years old.  I have never broken an axle, never replaced cones or bearings, and they're still as smooth (or smoother) than the day I bought them.

In contrast, look at this picture:



On the left is the Dura-Ace free hub axle, with cone placement indicating bearing placement.  On the right is the freehub assembly (missing the axle).  In the middle is the axle from a 2014 Mavic Crossmax SLR rear wheel - Mavic's top-of-the-line cross-country MTB wheelset from 2014.  The aluminum axle is broken in a VERY familiar place:  It's broken exactly where the drive-side bearings provide a leverage point for the hub bearings.  Mavic goes to great lengths to disguise from people that their hubs employ a hugely outdated technology.  Sure, their hubs *look* like the employ a "freehub" design, but they don't.  Mavic employs a quasi-modo hub design.  Their hub design uses a freehub - in the sense that the cogs are NOT attached to the ratchet and drive mechanism.  BUT their bearing placement design still has all the drawbacks and weaknesses of the very old-school bearing placement from the freewheel era.

Given a choice I will NEVER purchase a subset with the archaic freewheel-style bearing placement.  My Dura-Ace hubs are *ancient* by cycling standards. They've been THOROUGHLY abused by me over 24+ years.  They are as solid as I could possibly hope for:  Reasonably light, easy to work on, reliable and tough.  My Mavic axles, on the other hand have less than two full seasons on them, and I've already managed to break an axle.  Not a great track record.