Ergomo vs iMagic

iMagic vs Ergomo Pro wattage accuracy is on trial here as I have been dubious about the wattages being recorded by the iMagic and an element of how it seemed to be working. Having purchased an Ergomo Pro I was then able to match the two up and see what the differences are. My Ergomo was purchased from cyclepowermeters and installed during a visit on Friday morning.

It should be noted that I have set the scaling factor to 115 in the iMagic (i.e. for every 115W read as 100W) as I was trying to calibrate it against my polar kCal burn. The quick test seems to explain why I was still not convinced it was correct, but thought it was closer than it was.

The initial chart of a ramp up over 3 minutes shows how the iMagic over and then under reads against the Ergomo over a range with the top end out by upto 10%. Comparing a small stable time slice at 302W in iMagic mode this equated to 322W in Ergomo watts. At this point I was more curious as to what the diference was as I had a feeling it may have been due to wheel speed. The reason was that when training in fixed wattage mode on the iMagic it always appeared to feel easier at higher cadences, which encouraged you to increase your cadence... After looking at another part of the data it starts to make more sense, as it does get easier as the wheel speed increases on the iMagic, although not by enough to cancel out the differences.


Comparing wheel speeds on the second wattage test the two systems seem to be comparable enough over the range, although out by a slight amount. This may be partially due to the wheel circumference in the Ergomo at 2130 compared to the measured 2125, although the difference seems too small to make a >5% diference in speeds. Overall though once the axese are corrected the scales seem to match up for the test.




The correlation was quite good with an r squared of 98.14% for the formula of (Wheel mph = 0.903 iMagic mph + 0.6457)


Next was the second quick test but this time the iMagic was set to a fixed wattage mode and then increased over a period of time. The difference starts to become a lot more apparent with a slower wheel speed and a higher wattage as the accuracy starts to drift out considerably.

Increasing the cadence and wheel speed, while not altering the iMagic wattage it did reduce the real Ergomo wattage from a 50W error down to a minimum error of around 20W. The difference in wheel speed between 21mph and 24mph should not have made anywhere near a 30W difference, although the wheel was a shimano R550 with a conti trainer tyre on at 120psi.

Summary - I'm happy as my wattage is around 10% higher than what I was training with, instant watts !