Sunday, July 12, 2009

Time Is Limited, Train Effectively

If you are like most of us, you have limited training time. You have to train indoors and want to make the most of it. The closer your training device comes to a real outdoor pedaling motion, the better the results from your training.

The PFS provides a theoretically-sound pedal force over a full range of pedaling conditions including sprints and out-of-the saddle efforts and climbs, workouts that you can't do on trainers.

The PFS models power within a pedal stroke correctly. As a consequence:
  • Hills feel like riding hills. When riding hills outdoors one's cadence naturally falls. And so it does on the PFS. This is a definitive indicator that the simulated pedaling is correct. Trainers don't respond this way.

  • One can sprint out of the saddle. This allows you to train for sprints indoors without having to ride to a suitable training spot. One can train for sprints on a PFS; one can't on a trainer.
  • One can train to climb long hills out of the saddle. On long climbs one needs to be able to vary one's position. Training to climb out of the saddle allows this. You can live in flat Florida and still train for long climbs using the PFS. One can't do this on a trainer.

  • One can do standing starts. This is particularly useful for training for track events. One can't do standing starts on a trainer.

  • Although less obvious, on the PFS simulated flat courses feel like they should. Trainers just never feel right even when spinning easy.

  • By getting the force right at the pedal, the PFS allows one to duplicate indoors the subtle changes in position that come from increased power outdoors. Trainers don't get this right.


  1. Hi Tom,

    I'm a great fan of analytic cycling and have my own blog Cozy Beehive. Could you clarify, is this a simulator and trainer package all in one?

  2. It's one package. Rider controls are in the display computer. This is where the rider sets up the simulation. Resistance is controlled by a computer at the wheel. The computer at the wheel receives the simulation model from the display computer and controls the resistance 1000 times per second in accordance with the simulation model.

  3. From the first look it seems that resistance unit of your simulator is based on Eddy Current brake. Is it correct? If yes then how it can simulate realistic coasting?

  4. The momentum of the rotating portion of the eddy-current brake supplies enough momentum to maintain the speed of the rear wheel while a rider coasts for short periods of time. Further, the control circuit will slow the speed at a realistic rate. However, it won’t speed up the rear wheel.

    People have asked if it will model coasting down a long hill. It won’t. But the feature is doable. Since coasting down a long hill is not a common training technique, we choose not to implement it.

  5. Surely this is what Tacx have got with their Fortius software.

  6. Not at all, there is a huge difference.

    If one has ridden a trainer, any trainer, sophisticated or not, one knows that pedaling does not feel like riding outdoors. Ride up a hill outdoors. Ride outdoors down a slight grade with a tailwind. Ride both at the same power and cadence. These conditions feel dramatically different yet the power and cadence are the same. Why? When one analyzes the physics, one finds that the difference is a result of the difference in the instantaneous acceleration of the pedal. This difference in instantaneous acceleration of the pedal translates into different patterns of speed and force of contraction of the muscles and hence the difference in feel.

    The Pedal Force Simulator models the accelerations and makes the instantaneous acceleration of the pedal match the instantaneous acceleration one would feel riding outdoors.

    The more sophisticated trainers on the market allow a rider to select model parameters and then set a resistance that gives a target average power. Their instantaneous acceleration is wrong all the time even thought the average power and cadence are consistent with model parameters. Ride one. They feel wrong. One knows it instantly. Ride a Pedal Force Simulator. It feels right. An uphill feels like an uphill; downhill with a tailwind feels like downhill with a tailwind. One knows instantly its right.

    It matters. Riding well is all about pedaling well. Think about an example of pedaling wrong. Say one is fatigued and starting to loose some coordination and is still pushing at the end of the pedal stroke. The effort is going into stretching the crank arm. This is generating a small anaerobic effort at the end of each pedal stoke. This small anaerobic effort is creating a large energy requirement that the cardiovascular system has to support at a time when it is at its limit. This wasted cardiovascular capacity is not adding power to the bike. A little more coordination and cardiovascular capacity could be used for more power to the bike.

    All the trainers will load the cardiovascular system. The Pedal Force Simulator takes the next step and provides the correct speed and force of contraction to the muscles.

  7. Hi Tom

    I am wondering how the physical model is working. I guess it is modeled with a speed dependent resistance from things like the wind or the roads gradient and then a resistance which is linked to the forward acceleration of the bike and rider. Is this correct and if so is the current gearing used as input?

    Best regards

  8. Bike gears never enter into the analysis. It’s all done at the rear wheel.

    The Pedal Force Simulator measures acceleration at the rear wheel 1000 times per second and adjusts resistive torque at the rear wheel 1000 times per second such that instantaneous applied torque is always consistent with the modeled conditions. It uses a well defined, tested, and accepted model of the forces of wind, gravity, and rolling resistance acting on a rider.

    Think of climbing while seated verses climbing while standing. The legs feel different seated verses standing. Gears are different. The patterns of the instantaneous accelerations are different. The Pedal Force Simulator responds automatically to these different instantaneous accelerations to give seated and standing pedal experience equivalent to riding outdoors.