I've been using Polar Power setups on both my bikes for over a year, and up till now have been very pleased with the degree of consistancy through most of the gear comibinations (although it has to be said, not at low cadence in 39x23 or similar) However, one has just suddenly started giving strangely low readings - I'm buzzing along at 35kph and it's reading a steady 80w or so. A week ago it was fine and would be reading over 200w for similar perceived exertions.
The cadence and speed have continued to run fine from the power sensor. I've been through and checked all the cables, there's a little wear on the rear mech sensor but nothing much, and the battery is only a few months old. I've moved the chainstay reader a little closer to the chain, but that didn't make any difference. I've also checked the settings on the watch unit. I just wondered if anyone had any thoughts before I popped it in the post to Polar, as goodness knows when I'll see it again if I do that 😎
this is a familiar story - both my polar power meter and that of my training partner worked satisfactorily for about a year each, then all of a sudden the readings mysteriously became either way too low, or non existent.
first instinct was to check the proximity of all the sensors and change the battery, but to no avail.
in the end, having seen the value of power training but grown to hate the problem with my polar, i splashed out on an SRM (at a great additional cost that i did not incur lightly!) my friend is now contemplating this difficult decision.
i have had my two polar power units for 1 year and 1 3/4 years, and have rarely, if ever had a problem. i DID have a problem with erratic readings a few months ago and it turned out to the battery in the handlebar set. i checked the battery last since it was the newer of the 2 units and i just assumed the battery would have lasted longer.
assuming your chain weight & length settings haven't changed, and your sensors are properly placed, i would buy a $5 battery and start there.
Rob, I had a similar problem, especially when climbing in a low gear eg 39x25. It may have been due to the rear unit moving a little on the chainstay (which is likely as thats curved and the unit is flat, so no amount of zip tie torque will stop that, especially if you factor in a wet surface from rain). Resolved it by moving it a little, but as I realised the whole set up is sensitive to movement, prone to error and won't handle measuring sprints, am changing to power tap. Good luck 🙂
Another issue is the speed sensor. Mounting it too close can cause a double reading, making the speed HIGHLY inaccurate. Too far will also cause a problem...
Ditto on the cadence. IMHO, this is what is causing the error.
Also check for dirt on the chain speed sensor. Since it only works with ferromagnetic chains and most chain "dirt" is actually finely divided chain steel, buildup of this "dirt" can cause problems.
