Aero watts?

[djaustin]

Just an observation really. I have two powerpods on separate bikes paired with the same Garmin speed sensor, which I swap between front hubs. The red pod is on my fixed wheel road bike (candence is speed, of course). But today I swapped both pod and speed sensor onto my aero Giant Propel and went for a road race. The orientation is not exact, so the powerpod started with a tilt adjustment and then settled down. What I did notice after that is the watts were then consistently about 30W too high.

My likely explanation is 1) Frame and wheels on racebike are more aero. 2) Bike and rider are a few kilos lighter (no pannier for a start!) 3) Tyres have a lower Crr.

I've returned the powerpod back to the fixed bike for tomorrow's training loop, and assume that, after a further adjustment for tilt, all will be back to normal? I'll post some files later, but thought it interesting. Both bikes have a combined Garmin/Go Pro mount, but the Giant one is custom and does not allow for the locking of the powerpod (I insert a 2mm Allen key and rotate against that before locking down).

I think the 30W is in the right ballpark. My other powerpod is on my winter road bike, and gives consistent readings to the fixed bike. I do plan to run them simultaneously on one bike one day.