Is the bicycle hub gear about to make a comeback with Classified’s innovative Powershift product?
The popular hub gear
Many of us of a certain age probably remember riding bikes fitted with Sturmey-Archer 3 speed hubs before moving to more sophisticated machines with derailleur gears. In fact, you may be surprised to learn that the hub gear never went away and continues to be found on commuter, town and touring bicycles.
Since its invention in 1895 by American machinist Seward Thomas Johnson the hub gear has undergone continuous development. Top-end modern hub gears can be highly advanced with the near bullet-proof Rohloff 14 gear speed hub a favourite among touring cyclists – a far cry from Johnson’s rudimentary two speed hub. These days it is even possible to have the option of electronic shifting with Shimano’s highly advanced Alfine range.
The growth in popularity of e-bikes has been a catalyst for the development of better gear systems for bicycles due to the high levels of torque produced by electric motors. Hub gears arguably perform better than derailleurs in these applications, and some manufacturers even fit car-like internal gear boxes mounted at the crank.
In the conservative world of bicycle road racing, it is no surprise that the derailleur still prevails but that might be about to change. This season sees Belgian star, and former hour record holder, Victor Campenaerts ride the Classified Powershift two-speed hub in some of the world’s most prestigious races. Campenaerts is known to obsess over marginal gains so why has he decided to use a hub gear, and with only two speeds?
problem front derailleurs
Front derailleurs, as good as they now are, still give a bit of a clunky shift compared with the rear mech. There are many factors that can affect front shifting including the compatibility of the chain, shifter and rings; the sizes of inner and outer rings; the way the system has been set-up; the degree of chain tension; quality of lubrication and degree of dirt. So, often, if you are going to drop a chain during a shift it will happen on the front.
SRAM tried to solve the problem with a single front ring and a wider spread of gears on the rear cassette. This is now very popular in cyclocross and mountain bike riding but less so on the road where riders are more sensitive to big jumps in ratios. This is where Classified believe they have a unique solution.
They rather ingeniously saw the opportunity to do away with the front derailleur by developing a two-speed hub gear that is electronically actuated. The hub replaces the need for the two front rings by offering a fixed setting and a reduction gear of 0.7. In the fixed setting there is no effect upon the gears you have on your bike – they work as you would expect. But when you select the 0.7 ratio those same gears are now 30% lower. For example, if you have a 53-tooth outer ring the lower range will be roughly equivalent to running a 37-tooth inner ring.
Benefits of the powershift hub gear
Classified claim numerous benefits of the system. The speed of the shift is incredibly fast at around 150 milliseconds, which unlike derailleurs doesn’t require you anticipate the point where you need the shift to be complete. Unlike a derailleur it is possible to shift under heavy load and when stationary which has always been the appeal of hub gears on town bikes.
With a reduction gear of 70% it is possible to run a much larger chainring than usual. Road race cyclists tend to use a 39-tooth inner ring and a 53-tooth outer. The same inner ratio can be achieved with a 56-tooth ring using Powershift. In fact, Campenaerts has gone even higher using a 62-tooth solid front ring and larger sprockets on the rear cassette to keep the gearing within a rideable range. This strategy allows the chain to follow a more relaxed path across the chainrings, allegedly improving mechanical efficiency by reducing chain tension by about 30%.
Too good to be true?
To some this seems to be too good to be true, and it may be. The Powershift system adds rotational weight to the rear wheel, increasing inertia and potentially reducing acceleration. The complex internal mechanics of hub gears are also known to increase friction and reduce efficiency. A seven-speed derailleur has an efficiency ranging from around 98% to 99%, depending upon chain position. The reported range of efficiency for a Rohloff hub is from 95.8% to 99.5%. I would think that Classified have done their best to maximise efficiency but there is sadly no independent research to put numbers on it.
Powershift does present additional technical challenges over the more common derailleur. If you choose to adopt the system you will need to ensure it is compatible with your frameset and, if you use more than one pair of wheels you’ll need to ensure it’s built into each rear wheel you own. This adds considerably to a system which is already pretty costly: a carbon wheel with Powershift can cost more than £2,000.
Despite these issues, I do think this is an ingenious engineering solution to the problems associated with front derailleurs. Powershift in its current form may have greatest appeal for the recreation cyclist who might be willing to sacrifice a little efficiency for simpler gear shifting and a lower risk of dropped chains. I think it may be some time before professional riders and teams start adopting the system in large numbers. It’ll be interesting to see if it becomes a commercial success.
If you want to find out more about the history of road bicycle gears you can read my blog post here.