A bike geek question posted on twitter from the editor in chief of velo news, “How is that riding indoor trainer, at what feels like tempo, my HR pegs at 100-115 bpm? Tempo HR on road ~130-145”
Hilarious replies… https://twitter.com/nealrogers/status/419984685926592513
We wrote the Ed. with a quick calculation & explanation. Below are excerpts for your edutainment.
An accurate simulation of cycling requires both inertia (resistance) and momentum (tendency to stay in motion).
Resistance is easy to simulate with any brake (e.g. just how a brake stops a wheel when you’re holding a bike off the ground). However, momentum (the tendency to stay in motion) is tough on indoor trainers because it requires a very large flywheel.
Without adequate momentum on an indoor trainer, it won’t feel right because the pedals stall at top and bottom-dead-center, which causes riders to restart their pedal stroke and apply force in the wrong part of the pedal stroke, which raise lactate, increase PRE (Perceived Rate of Exertion) and prevents real/actual power output.
Both inertia and momentum are required on indoor trainers to obtain accurate PRE, but it’s momentum that provides a real biomechanical advantage to cyclists as it moves riders’ feet/pedals deeper into the pedal stroke before resistance is sustained by the rider. This effect increases the leverage riders have over the pedals, as the legs approach extension, which provides the biomechanical advantage.
So, 200 Watts is not 200 Watts on all trainers because the momentum characteristics differ, and 200 Watts indoors doesn’t transfer to 200 Watts outside, because momentum typically supplied by trainers are inadequate.
This trainer solves the age-old problem on indoor trainers equations of motion which equate indoor and outdoor riding: http://goo.gl/SQm2lj
The trainer used by the Ed in chief seems off by a factor of three (3). Joules comparisons were done at various speeds: i.e. linear kinetic energy of rider vs rotational kinetic energy of flywheel. Here’s the leisurely 17 MPH comparison:
-82 Kg’s (Rider + bike)
-Kinetic Energy of a rider in Joules @ 17 MPH = (0.582(7.6)^2)= 2368.16
-mass of flywheel (~8 lbs.) 3.64kg
-radius (flywheel) 0.10m
-Moment of Inertia (.5xmass*radius^2) 0.01 kg-m^2
-Pedal Speed (RPM) ~76 rev/min
-Drive Ratio with 2" roller 35:1
-Flywheel Speed (RPM) 2660.00 rev/min
-Flywheel Speed (RPS) 44.33 rev/sec
-Flywheel Speed (rad/s) 278.41 radians/sec
-Joules on the trainer = 727.40
*3-fold difference in Joules (2368/727) between the trainer & real riding, as measured in Joules/energy