Inboard chain top view
Outboard chain top view
Elevation view
Mount, side view
Mount, close-up
Detail of cadence magnet
There have been many reports that power readings from a Polar S710 power unit are sensitive to the way it is installed, and some users have switched to either the SRM or the Power Tap in their frustration.
I hasten to add that I tend to hear from people who are having problems, so I cannot comment on how common these problems are; I can only say that these problems do exist. Some S710 users appear to have no problems at all, and report good results. Nonetheless, it appears clear that the S710's power unit can be sensitive to the way it is installed: a good installation may produce reliable data, but a bad installation definitely does not. Worse, the installation instructions are not clear enough--the people who report problems have often tried reinstalling several times.
If you would like to see data from a poorly-performing S710 and how to test to see if your data are reliable, click here.
Here are links to three sites that show S710 power units:
Here are some photos of (yet) another S710 installation. Bill Pence spent quite a bit of time on this installation, in part because his bike has curved chainstays and a triple chainring. Bill says:
"The Polar is certainly not an easy gadget to mount. I suppose if you had the right bike (whatever they used to develop the mounting system) it would be fairly straightforward. As it is I would classify their...'mounting scheme' not ready for prime time. That said, if you figure out how to set it up, it works quite well. [The chainstays on Bill's bike are curved] and so I had to get creative. I did take extra care to insure that the main axis of the sensor was parallel to the center of the chainline. I have a Record 10 speed triple and the envelope of chain angles and heights is pretty extreme. If you are running a double it might not be such a problem. The biggest problem I had was in getting the sensor close enough to the crankarm to see the cadence magnet. When you are in the 53x13 there is very little clearance between the crank and the chain. The chain must be within spec vertically and needs to pass over the sensor laterally, even if it only skims the edge."
Click on these thumbnails to see expanded images.
Inboard chain top view
Outboard chain top view
Elevation view
Mount, side view
Mount, close-up
Detail of cadence magnet