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After using the SRM wireless for nearly 4 months now, I was wondering what it would be like to get and use the much cheaper Polar W.I.N.D. power meter to add to my CS600 that I have had for about 16 months (bought when my Polar 720i died, replaced under warranty). The SRM is widely considered the gold standard of power meters and their pricing reflects this. A SRM, if you didn’t already know measures force applied through several strain gauges in the crank. This force multiplied by the lever arm gives torque and multiplied by cadence (rpm) you get power. Pretty straight forward physics.

The Polar system measures chain tension and chain speed to give power applied. Chain tension is measured by detecting the vibrational frequency of the chain. So, with the Quid plumbing new depths versus the dollar I ordered a sensor kit from ProBikeKit (~200 GBP, $295 USD shipped). After about 9 days, I got the part in the mail and installed it on my TT bike (converted Kuota Kebel).

My thoughts behind this is that I could get a reasonably accurate power reading for training and pacing during time trials. And it would be with both my training wheels and my disc wheel.

Setup took about 30-40 minutes to get all the parts out and installed. The kit comes with bolts for Shimano (2 types) and Campy. I have a SRAM Force RD on my bike. I took the bolt out and looked it. Both the Shimano and the Campy looked right on the thread end, but I went with the Campy one due to the taper on the head end. (The Polar website suggests to call customer service, but they were already closed for the day.)

Chain speed sensor on RD.

So with all of I fired up my CS600 and started to look at the settings. The required settings are:

• Chain weight: 304 g (0.206 g/mm)
• Chain length: 1473 mm
• Seatstay length (C/C): 420 mm

After confirming it all worked, I weighed my chain (Ultegra) and the numbers for my chain were 251 g / 1360 mm (0.185 g/mm) and my seat stay was 400 mm. So I put the new numbers in a brought my bike upstairs for a 20-25 minute recovery trainer ride / test drive.

Battery pack on seat stay & chain vibration/tension sensor on chain stay. Note the chain sag…the sensor has a strong magnet in it.

The data that was coming out of the meter seemed to be reasonably accurate. I was doing a recovery type ride in the 190-200W range which felt about right. I took it up to higher wattage (~300W) to see if it felt correct and it did. Once I move the speed sensor to the rear wheel, I can make a direct comparison since I have so much speed/watt data for my Kinetic trainer to match it up with my SRM. But even if it is off 10% from my SRM, it will helpful in working on power / position on my TT bike by allowing comparison from day to day or position to position.

Here is the graph from my ride. One of the interesting quirks that I noticed right away when testing is that when backpedaling, the power reads crazy high (500W+ it no power getting applied at 1:30 and 11 minutes). For my purposes, I doubt this will be an issue since who really backpedals on the road?

I am not sure about the crazy HR readings. This was an easy ride that I doubt had a HR ever about 110-120 bpm. This is not a new problem, I had these issue on the road before.

So far things are looking good. Searching for info/opinions on the internets before bought this system lead me to believe this system is a unholy nightmare. At this point, it seems like a good value especially if you already have a CS600 head unit (half the cost if you are starting from zero) and/or for a second bike situation like this. I will give an on-the-road type report when I give it a go next week. For now, I am headed west to race the Hell’s Kitchen road race in NW Arkansas (near Fayetteville).