The Jones Report
Understanding Rear Hubs…
A modern bicycle is the pinnacle of refinement of a concept dating back to the early 1800’s. Back then it had no pedals, gears, pneumatic tires or brakes. It was heavy and unwieldy and offered no advantage compared to travel on horseback or by carriage. How things have changed. In two hundred years, bicycles have gone from being a rich man’s toy to the most efficient means of transport ever devised. There are many stories illustrating the gradual improvement in bicycle design, but I want to narrow the focus and talk a little about the progress that rear hubs have made since the 1970’s; in particular, rear hubs designed for derailleur systems.
In 1869, the bicycle freewheel was invented, allowing the rider for the first time to rest his or her legs while the bicycle continued to roll forward. Fast forward to the early 1900’s and witness the the multiple freewheel, allowing the rider to maximize speed for the same effort. From the 1920’s to the present day we’ve seen a steady progression in the number of gears (or sprockets) available to riders, from two gears all the way to the current maximum of twelve sprockets. There’s a particular moment when hub design changed, facilitating this continuous march towards friendly complexity; I’ll explain when it happened and why.
Hub Design Changes
Up until the late 1970’s bicycles employed multi-speed freewheels, a device that combined the sprockets and a ratcheting mechanism in a single unit; this unit threaded onto a rear hub. All was well and good when we had four or even five geared freewheels as standard equipment; but, as the number of sprockets increased, hubs underwent a progression from 116 mm wide to 130mm wide, to accommodate the extra gears. The unsupported length of the rear axle, from the drive-side hub bearing to the frame drop out, became ever longer, allowing the axle to flex, bend and eventually break. Until Shimano introduced their “freehub” design in 1978, cyclists had been dealing with an ever-increasing frequency of axle breakage. The Japanese company’s design made broken axles a rarity.
In a freehub, the ratcheting mechanism is incorporated into the hub body, allowing the drive side axle bearing to be located far closer to the end, minimizing the length of unsupported axle. The sprockets, liberated from the ratcheting mechanism, simply slide onto splines on the freehub body. When freehubs were introduced in the late Seventies, six speeds were the default. It’s taken roughly 35 years for us to arrive at Sram’s 12-speed Eagle system. This progression would not have been possible without freehub designs pioneered by Shimano, Suntour and Maillard; with regard to bicycle design and its continuous refinement, we really do stand on the shoulders of giants.
Benefits From Rear Hub Design
Mountain bikes have benefitted even more than road bikes from a more durable rear hub design. Think of the stress that downhill competition places on ALL parts of the bike, but the wheels in particular. It’s a happy coincidence that off-road riding arrived as freehub design became the norm because I really don’t think the older hub/freewheel design could have sustained the demands of off-road riding.
Disc brakes for bicycles are a breakthrough that would have been impossible, if not for the durability and reliability afforded by the freehub design; stresses absorbed by the hub are phenomenal when it is part of the braking system. Without the rigidity provided by the freehub design, I reckon it would be close to impossible to eliminate disc brake rub.
I started this article thinking about progress in bicycle design and the benefits it offers to us, if we wish to adopt them. And, although some older bicycles cannot accept wider spaced hubs and/or disc brakes, I’m still thrilled by the progress we’ve made. I’m certain that we live in the true Golden Age of bicycle design. It does make me wonder, though; where will we be thirty years down the road?
John Jones is owner and head wheel builder of Jones Precision Wheels in Goleta, CA. He works alongside the frame builders at Stinner Frameworks.