Originally Posted by
Looigi
On a trainer, you can simply determine the force applied on the drag mechanism. This can measured, or calibrated. Calibrated force with magnetic drag mechanisms is much more straightforward and less problematic than with mechanical systems. So, I'm saying it is possible for power to be reasonably accurate on this trainer, not that they've done it right and it is.
This entire trainer costs about the same as a power meter for a bike, which suggests it would be unrealistic to expect it to include that kind of power measurement.
Measuring power is fairly easy.
The power meters for bikes are that expensive because they have to be extremely light, extremely small, extremely sturdy and accurate under extreme cold, heat and vibration.
This is the main reason they are that expensive.
Imagine two pedals linked to a simple electric alternator.
If you pedal ... it makes electricity at a certain voltage.
If you measure the voltage and if you measure the energy lost through your device ... you have your wattage right there.
Measuring to the extreme how far a spring is being pressed, as the expensive powertap systems do ... is much more difficult.
The bike depicted here still is quite expensive I recon.
Much cheaper bikes can be had and possibly converted to better suited devices for the specific rider.
My indoor training bicycle only cost about 250€ ... I converted it to have a specific TT-style handlebar and position.
The power it measures is probably not completely accurate but if I compare the numbers to real world data it can't be too far off and comes over as quite reliable.