How accurate is the power function of the Ciclosport HAC4? How does it compare to the Polar unit?
No it's a big guess! uses weight and speed to calculate power. ride into a 25mph head wind with a slight grade of 2% it's way off.
The HAC4 calculates power like the poster above said. I have the HAC4.
I believe the Polar unit actually measures power by measuring strain or something on the chain.
There's other products that will measure power directly/better. It all matters how much you want to know and spend.
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Originally Posted by Bontrager
I believe you are correct. I actually read a report that compared the different systems that measure power. At the top of the list was the PowerTaps being the most accurate, with the Polar unit slightly behind the PowerTaps. What they didn't like about the Polar unit was that the power reader is a bit difficult to work with because it seems to slide off the chain or around the chain at times.
Both units are pretty expensive, although the PowerTaps is far more expensive than the Polar.
I had a HAC4 and now have a PowerTap and the difference is huge. Do not use the HAC4 as any kind of power meter - it is simply too far off. Perhaps indoors with no wind or gradient it would be closer but in the real world it is way off. Keep in mind that the HAC4 only records once every 20 seconds so it often 'misses' gradients and does not take into account winds.
For example, I compared PowerTap recordings to HAC3 recordings over the same route/conditions and the readings averaged 30-50% off and sometimes even higher on climbs.
I liked the HAC4 and think it is a fine cycling computer but it is worthless as far as watts go. . .