Polar Power Meter

I was looking to try out a power meter to see if I could improve my training. This past year I picked up a polar power meter. I selected this device primarily because of the cost. It's cheep (compared to other power meters) Basically it measures the tension in the chain and rate the chain is moving to get power.

My setup was to their specifications, including weighing the chain on an analytical balance.

Experimental:

To quantify how well it works, I carried out a test. Basically I put my bike on a trainer and pedaled to maintain a constant speed. A trainer is a fixed resistance; the wheel speed was maintained and then I shifted through the gears, pedaling at different speeds to maintain the same speed. The idea is, if the resistance doesn't change and the wheel speed doesn't change then the power output should be the same in all gears.

Results:

I mantained the wheel speed at 15.4 +/- .2 mph in all gears.

Obviously there is a nice trend in the data. Nice S curve (actually thats not good).
The average power output was 144W with a standard devation of 23 Watts. At the maximum the power meter was off by +35 W on the small cog side and -29 W on the large cog side.

Conclusion:
This device... Sucks. A 64 watt range was generated just by shifting gears. Most power meters on the market publish an accuracy of 1.5-3%. This polar power meter is accurate within 25%. I bet most people could guess better than that!

Full Disclosure:
The power meter I had was the older wired version. I went through two of them because the wires are a real weekness and they broke. Both had the same performance so don't think you'll get a better one. The new power meter might be better, at least they did away with the wires.

Future Plans:
I purchased a PowerTap. Looks for more updates soon.