Wednesday, February 20, 2013

Force at the Pedals

Trainers and rollers don't feel right.  

It's not enough to get average power right.  Many trainers get average power right.  But they don't feel right because the force at the pedals is wrong.  And without correct pedal force, muscle fiber recruitment patterns are wrong.  

The Pedal Force Simulator gets the pedal force right.

Force at the pedals is a function of the acceleration of the rider subject to forces from wind, gravity, and rolling resistance.  The Pedal Force Simulator's computer measures a rider's acceleration and sets the resistance to be consistent with rider mass and forces in the environment being modeled.  It does this 1000 times per second so it's correct at every instant.  This means that the muscle fiber recruitment is the same as riding outdoors.  It means one's indoor training is much more effective than on trainers or rollers.

Have you ever wondered why one can't stand up on a trainer like one does outdoors on a hill?   it's about force at the pedals.  One can stand on a Pedal Force Simulator because the pedal force is correct.  Sit or stand, the pedal force is always correct.

And the more specific the training the better the results.


  1. I "cheated" and just mounted a brake disc from a Camry (approx 11 lbs and 10" diameter) onto the teensy flywheel on my trainer. I did some rough calcs and the stored energy in that flywheel is pretty much equivalent to the stored energy in my body + bike frame + wheels at the same speed. It feels much better than riding a trainer with the typical 1 lb, 4" flywheel. The only difficult part was balancing the final assembly, but I think I got it pretty close by just repeatedly spinning the flywheel and drilling a hole at the bottom when it stopped. I can stand on the pedals and actually coast for a reasonable time.

  2. The stored energy in a flywheel can be very large. But that is not what makes force at a pedal feel right: it's the acceleration felt at the pedal.

    A trainer with a large flywheel certainly feels better than one with a small flywheel. Kurt makes one. I would recommend a trainer with a large flywheel to anyone riding a trainer.

    I did an analysis of an idealized flywheel trainer. In the trainer was a flywheel and around the outside of the flywheel was a strap. One end of the strap was fixed; a weight hung from the other end. (Just like what one would find in a physics text book.) I analyzed the acceleration felt at the pedal for various combinations of weight and flywheel inertia. And for particular combinations of flywheel rotational inertia and weight on the brake, one could simulate a particular cycling enviroment such as a hill or speed ;on a road. However, the setup would only simulate one very small part of a typical cyclist environment. As I recall, the mass of the flywheel was in the 100 pound range.

    A Pedal Force Simulator performs a theoretically sound simulation of the acceleration felt at the pedal for a full range of environments encountered by a cyclist. The difference in feel is dramatic. It gives the correct muscle activation for ideal training. Trainers don't activate the muscles correctly. Yes, the legs go round and round, but that does not mean that the muscles are activated at the correct speed, acceleration, and force to simulate cycling.