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I am looking for an answer that may include watts and/or calories per hour only. Please do not discuss wheels, tires, bearings, body weight, frame weight. Just help me understand the physics of adding 2lbs- one on the right foot and one on the left. Assume 170mm pedals with mid range cranks (Shimano 105) at a cadence of 84 RPM. Ignore air friction, rolling resistance, etc. Assume a body weight of 150lbs, if you need one. This is a physics problem, not a discussion about how economics nor opinions about whether it is a wise decision or not. Thank you for helping.

Thank you all for your input. Good feedback.

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    Can we also assume spherical cows in vacuum? And more importantly, what are you actually trying to understand?
    – ojs
    Commented Oct 27, 2022 at 15:19
  • Since this is a physics problem, why not ask it on Physics?
    – DavidW
    Commented Oct 27, 2022 at 16:41
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    @Criggie: People start and stop pedaling much more often than they start and stop the whole bike.There is also a difference in rotational velocity (wheels usually spin several times faster).
    – Michael
    Commented Oct 27, 2022 at 18:11
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    @ojs Frictionless spherical cows, of course!
    – MaplePanda
    Commented Oct 27, 2022 at 22:10
  • 3
    I’m voting to close this question because this question is theoretical and belongs on physics.stackexchange.com
    – mattnz
    Commented Oct 27, 2022 at 22:49

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Adding mass with radial symmetry (i.e. to both crankarms or pedals or equally spaced around the chainrings/spider) will obviously increase rotational inertia and the overall mass of the bike, acting like a flywheel. If you were pedaling with a completely constant rotational velocity it wouldn’t affect your performance at all (aside from a very small increase of friction losses from the added mass).

However, humans are not pedaling at a constant rotational velocity. Aside from the obvious losses when braking and stopping I think there is also a small variation in velocity throughout the pedaling cycle. It’s most obvious when riders get out of the saddle and are pedaling as hard as they can.

The increased rotational inertia would “force” you to pedal at a more constant velocity. I’m not sure that’s actually a good idea from an ergonomics or efficiency point of view.

Oval chainrings are a much nicer solution to get more constant torque without adding a flywheel.

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  • Agreed. There would be a calculable but imperceptible loss of speed at a given power due to the added weight. Something in the range of 0.02 mph. See gribble.org/cycling/power_v_speed.html
    – Adam Rice
    Commented Oct 27, 2022 at 16:54
  • @AdamRice ...on the flat, with more decrease as the road pitches up. And with a benefit as the road comes back down the hill.
    – Criggie ♦
    Commented Oct 27, 2022 at 17:16
  • If you really want to increase your resistance, ride with a drogue chute. Runners use them.
    – Adam Rice
    Commented Oct 27, 2022 at 20:49
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    @AdamRice Thank you for the link. Criggie thank you for the comment. I am trying to increase the DT drag and/or foot inertia with pedal weights on practice rides to increase performance on race day. I have noticed that adding foot weights helps me and I am seeking a claim such as "adds an average of N watts per hour on flat rides" as drivetrain drag. Novice riders will have less rotational inertia as their feet pause and accelerate at different points in the pedal stroke. Perhaps my foot weights will help strengthen riders to smooth out the weaker parts of their stroke.
    – Ben Marshall Berg
    Commented Oct 27, 2022 at 20:52
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    Confirmation bias is by the way a real thing and could explain why things like this seem to help.
    – ojs
    Commented Oct 28, 2022 at 1:26

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