This is a question for the mechanical engineers on the forum. This bike is a very interesting concept using a shaft drive to a seven speed internal geared Shimano Nexus hub.
I’m not sure about mechanical effeciency vs a chain/derailleur system, but the shaft drive would be cleaner and require less maintenance.
I can certainly visualize this system as being a better way to go for commuter bikes, but would suspect that with only 7 gears it’s not suitable for high performance applications. Shimano and Sturmey-Archer both have 8 sp internally geared hubs, but until there is either more gears or some sort of a continuously variable internally geared hub offered, chains and derailleurs will be used on road race/tri bikes for awhile yet.
Still, I love the concept and suspect a more advanced version of this could be the future. Any comments?
Have a look at their website. They offer two Police bike models as well as mountain, hybrids and cruisers. All the bikes have internal hubs with shaft drive. They only offer the one road/touring bike however.
I had some experience with these drivetrains doing research in graduate school and for human powered vehicle competitions. The real problem with these types of drivetrains is the frictional loss in the system. Any change in the direction of motion results in a loss in efficiency. Shaft drives were actually popular on racing bicycles used at the turn of the twentieth century, as they offered a none slip design when compared to early cog/chain drives of the day. Major Taylor was reknowned for his success on a shaft drive bike. However, as the need for more gears developed, manufacturers shifted towards development of chain drives. The frictional losses in a shaft/internal hub can be significant: >30% depending on component design, seals, and lubrication. For commuter bikes, where efficiency can sometimes be secondary to weather resistance and reduced maintenance (from the sealed system) these designs have proven successful. In a more performance oriented system it would be extremely difficult (if not impossible) to mimic the effciency found in roller chain/cog designs. An interesting future possibility for this could be the Nuvinci hub design, as it does not use a planetary gear set, increasing the efficiency. It still wouldnt be as efficient (due to changes in the direction of motion), but it could start to come close with intense development of low drag seals, and ceramics. It would cost a fortune though! Interesting topic for discussion none the less
not sure about the shaft drive, but there’s an internally geared hub around by Rohloff that’s getting good reviews (they’ve had some at NORBA XCs a while back IIRC).
I think we will see the initial developement of internal “gearbox” bikes in the mountain bike world. Mounting a fragile parallelogram out on a piece of aluminum next to branches and rocks is a disaster waiting to happen and riders especially in freeride and downhill break a lot of derailleurs. I know at eurobike more companies than ever were showing “gearbox” bikes with a transmission mounted in the middle of the frame.
I think it will take a revolutionary design to change road/tri bikes over.
