Motorized bike drive shaft?

Discussion in 'General Questions' started by bikejock, May 12, 2015.

  1. bikejock

    bikejock Member

    I've seen bicycles and motorcycles that use drive shafts instead of chains so I was thinking, has anyone ever thought of making a drive shaft for a motorized bike? I would like one for my 4G kit someday. I wouldn't need to worry about the chain slipping off or the chain bumping against my tire if I could get a drive shaft hooked up some how. It would also mean less moving parts compared to using a chain drive. I think it would also look pretty cool.

  2. butterbean

    butterbean Well-Known Member

    If your chain has proper alignment and tension and you don't run tires that are too wide for your drive chain, you wont have any of those problems. Changing a tire on a bike with a drive shaft would be a major pita. Not to mention what it will probably cost to have one made. And not many people are interested in them. I think that's why no one has yet. There are a few people in this hobby who probably could, but I'm sure there is a good reason they have not.
  3. Slogger

    Slogger Member

    Look at the top fuel bikes, they use chains. For high powered machines the chain and sprockets are the most efficient drive, for lower output bikes a belt drive is a little better.
    Shaft drives are for longevity and low maintenance. They almost never break or need replaced.
    The drawbacks are several. Weight, cost, handling and efficiency. Notice that the motorcycles that are shaft driven are usually longitudinal engines, like a BMW Boxer or a Honda Goldwing. The crankshafts rotate in the right plane for a shaft drive. At the rear there is a gearset that changes the rotation 90 degrees to drive the wheel. Each time you pass through a 90 degree gearset, you lose a bit of power. With an engine like a CG you'd have to have two 90 degree gearsets, one front and one rear.
    If you have a suspension in the rear, the shaft will make it stiffen up under acceleration and droop on trailing throttle.
    A good toothed belt would be best on a CG, but the cost and inability to have a standard length belt in the kits make it a non-starter. You can't take a few links off a belt.
    The chain rules, for now anyway.
    I would say that once it is aligned and tensioned right, on these bikes they are just about trouble free. I don't even worry about it jumping off, it's smooth and quiet as a belt, almost.
  4. crassius

    crassius Well-Known Member

    probably worth looking at a drive shaft bicycle to see how it works
  5. Slogger

    Slogger Member

  6. crassius

    crassius Well-Known Member

    I've always felt that anything that makes a bicycle fast, makes a motorized bike bad - I want a really heavy frame & fat tires - if someone fitted a jackshaft to that pedal crank, it might be OK, but an extra $800 kills it for me
  7. bikejock

    bikejock Member

    So I guess we're stuck with the traditional chain drives for now. The rear drive is the thing I probably worry about the most. One reason I'm trying to go idlerless with my current build. No idler means one less part I need to worry about

    A chain (if you have wide tires) bumps on the tire wall because of the tension requirements. With a drive shaft there's no need to worry about tension or it bumping the tire. But yeah it would be a pain to remove the wheel on a drive shaft system.

    Also you wouldn't be able to go to a smaller sprocket to gain more speed. You'd also need a completely custom rear hub to support the drive shaft.

    I've seen bicycle drive shafts and they can be made small and fairly light. Basically a motorized bike drive shaft would just be a little more heavy duty to handle the torque and stress.
    Last edited: May 14, 2015