Did you think that a bicycle drive train can only be operated with a chain or with a transmission belt as seen more recently? A much older solution now came back into fashion: the transmission shaft. Used for some motorcycles, it was borrowed and slightly adapted to bicycles.
What you should know is that the first shaft drive transmission bicycles were used immediately after World War I, but soon after this technology was left to shade until the 80s, when some new models appeared.
What are the advantages of using a shaft transmission?
Pedaling across town on a shaft drive transmission bike, I immediately noticed some undeniable advantages. Silence is welcome but it is rather strange, as it sometimes gave me the impression I was riding an electric bike. Then, the whole system is well hidden, so you can be sure your clothes will remain clean, while you also won’t have to bother with the maintenance issues required by chain drives.
Feedback is similar to the one a chain has to offer, but calculations show us a 3% loss of power for the driveshaft, while for the chain we have to consider only 2%. However, if the chain is not properly lubricated the loss of power increases!
The bicycle’s look also gets much cleaner and simpler, and an untrained eye could easily confuse the shaft with the chainstay, until he or she notices that… there’s no chain at all!
Another advantage of the shaft drive is that it requires neither chainrings, nor sprockets, as it follows such a different philosophy than bicycles with chain or belt drive.
If your rear tire runs flat, it is easy to remove the wheel. Also, service life for a shaft drive can reach up to 30,000 km.
Are there any disadvantages?
Yes, there are. Weight is one of the biggest drawbacks of this system. It is hard to believe that you can buy a shaft drive bike to weigh less than 15 kg. You may come across a few models, but for sure they will be expensive. For a city bike, whose weight is not crucial, a shaft drive is feasible, but for a mountain bike, things get a little more complicated. Also, this drive train can not be simply be adapted to a usual bike, as you’ll have to buy a special frame that allows you to install it beneath the chainstay.
How does it work?
The system is quite simple. Movement is transmitted through the bottom bracket’s axle to the rear wheel thanks to the shaft drive. As you can see in the picture below, a system of gear wheels is responsible for transferring movement from the shaft to rear wheel’s axle.