Monday, April 1, 2013

Quad Cycle

Going Fast Week continues here at OPOD with this picture of a quad cycle. These guys have figured out the way to go faster is to put more people on the bicycle. I do wonder how the math works. Certainly 4 people pedaling in line could go faster than one person, but they would not go four times as fast. I wonder what percent speed advantage you would get for each additional person over one. The picture was taken in 1898.


  1. Interesting old bike.
    The advantage probably depends on not only the bike but the weight of the extra person as well as his ability to pedal .

  2. There appears to be some complicated distribution of power here. Note the different sizes of the crank wheels.

  3. I think adding people to speed up is a statement of the law of deminishing returns. In other words, each additional person will not proportionally increase the speed because the bike will be heavier and coordination of all cyclist will not be the same.

    Looking at the tires, I would think any additional people would require a larger set of tires which would increase the drag on the whole unit.

    I guess that an infinate number of cycelists would result in a near zero speed!

  4. Neat photo. Not sure on the physics of it, but I'd agree with PJM that it would not be 4x faster with the added weight and drag. Looks rather too cozy to me.
    -Anne K.

  5. What a great image. So many fun captions to consider.

  6. They have four times the power, and about the same drag (tire drag is negligible), the chief form of drag being air resistance.

    But power is proportional to speed cubed agaist air drag, so they'd go the cube root of 4 faster than one rider, or 1.587... times faster.

    Speed cubed because the drag force goes like speed squared (you hit twice as much air twice as hard if you go twice as fast), and one more power of speed because you apply that force over a greater distance per unit time.

  7. Ultimately you're speed is going to be limited by the gear ratio of the sprockets and the input speed of the cranks. More pedelers is not going to create more speed...but it will certainly create more power or torque. It's like comparing a big engine Vs a small engine in a car. They will each get you going the same speed because of the gear ratio in the axel. But the bigger engine will have an easier time keeping the speed up or pushing you up a hill.


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