If we were to follow Stephen Colbert’s example and let the market be the arbiter of all things, then Polar’s first generation power meter was a flop. I don’t know a single person who still uses one, and those who did don’t have many good things to say about it. Now Polar is back with a second version, the CS600 with Power. While the essential components and algorithms of power measurement remain unchanged, they’ve been reconfigured for easier installation and made wireless.

 

What is it?

 

The unit is actually a few separate modules. You can buy the CS600 ($419.95) as an HR computer only, then add a wireless fork sensor ($54.95) to make it a cyclometer. A cadence sensor ($54.95) is also available. Finally, the Power Output Sensor ($359.95) can be added to make the whole package a power meter. Or you can buy everything together for $709.95 (the package doesn’t include the cadence sensor, as the Power Output Sensor has one built in). Correction: the fork sensor is included in the base unit for $419.95.

 

The computer is chock full of more bells and whistles than can be covered here. My favorite is the live readout of your left/right output. I’ve always had a severe imbalance in my pedal stroke, and no amount of time spent on Powercranks or one legged drills could fix it. But the instant feedback of the Polar readout got my left/right ratio from 40/60 to 49/51 in a matter of weeks. 

 

The CS600 can also measure the roundness of your pedal stroke. On a scale from 1 to 100, with 100 being perfectly round, 30 is very good. Interestingly, I’m easily over 30 on the rollers, and way under 30 on the road. You can also select intervals on your workout to see if your stroke breaks down under pressure. Another cool feature (which I didn’t use) is the ability to upload workouts to the computer, and then having it cue you for your intervals.

 

The Power Output Sensor works like an electric guitar. A magnetic pickup/power sensor sits next to a string/chain and registers the pitch of the vibrations. The pitch is dependent on string/chain length, density, and tension. You measure and input chainstay length and chain weight and length (from which the CS600 derives density), the sensor reads the pitch, and the computer calculates chain tension, which is your pedaling force. Another sensor mounted on the lower derailer pulley measures chain speed. With force and speed you get power. Simple and foolproof, right?

 

Installation

 

Well, apparently not. Unlike strain gauge power meters, the components of the Power Output Sensor aren’t neatly tucked away in a controlled environment. As you shift gears, chain to sensor distance and chain length change. Road vibrations add noise to the data. Chain density is measured by the user, and is only as accurate as your scale. Amazingly, for a device that’s so dependent on proper installation for good results, the instruction booklets (each module gets its own booklet!) are terrible. Here’s some tips I gathered from talking to the Polar people, none of which are in the booklet:

 

*The pickup resides under a round dot on the sensor unit. That dot needs to be at the midpoint of the chainstay, where the signal is strongest and purest.

 

*Rubber risers are supplied to lift the sensor up to the chain. You’ll need to double them up to get the sensor close enough (the gap should never exceed 3cm). Polar recommends a 2mm gap when you’re in the small/small combination, but since you’ll probably never use that crossover gear, the chain can be touching in this gear.

 

*The cadence magnet needs to be oriented horizontally when the crankarm is at 3/9 o’clock.

 

The good news is that it’s just as easy to install the unit correctly as it is incorrectly, and after a couple of tries it can be done in a matter of minutes. You could easily remove the power sensor for a big race and use the CS600 as a cyclometer, then reinstall for training.

 

So does it work?

 

I put in a few hundred miles with the CS600 alongside a Powertap, then compared numbers in Cycling Peaks WKO+ (check bottom of article for data). After several rides it became clear that the Polar was reading about 6% higher than the PT, so I inputted a lower chain weight (247 grams / 1.06 = 233 grams). Since tension is directly proportional to chain density, the Polar power numbers dropped 6% as well. Once I did this ‘calibration’ the two power meters matched very well, on the road and on rollers. The numbers for entire rides were always within 3% of each other (except for one ride, see data section below).

 

The first thing you notice while riding with both power meters is that the CS600 reacts to wattage changes slowly. The CS600 needs to take a few seconds of data to filter out stray road vibrations from its readings, so if you accelerate or deccelerate, it’ll take 3 or 4 seconds for the readout to catch up. As a result, the CS600 will miss big spikes in power – you won’t be able to register gawdy max wattage numbers. But for real life training situations, the CS600 is more than accurate enough.

 

Once I got things pretty squared away I did some tests. First I rode 2 minute minimum intervals without shifting, hoping to see if accuracy varied with chain to sensor distance. I really couldn’t discern a trend, though the CS600 did pretty badly on this test. However, this was a pretty flawed test, as I was spinning at 130+ rpm’s in some gears and 40 in others. True, this is the kind of thing that doesn’t bother strain gauge based power meters, but the CS600 is optimized for typical riding situations.

 

Next I tried some 5 minute intervals at 210, 230, 250, 270, 290, and 310 watts. I hid the Powertap display from myself so I could only see the Polar readout. I wanted to know how well the CS600 worked as a workout tool. In other words, if I targeted a certain wattage for an interval, would the CS600 be accurate enough guide me to the right wattage? The CS600 did remarkably well there, especially as the wattage increased. It was harder than using a Powertap, as the Polar’s delay had me yo-yoing with my effort until I hit a piece of road with a steady grade. But based on this test, I’d have no problem doing all my training with the CS600.

 

Time for Hate

 

Ok, here we go. First of all, it’s ugly. The CS600 really junks up your rear triangle. Secondly, there seems to be some QC issues with early runs of the CS600. There’s an enormous message board thread detailing transmission dropouts, with the likely culprits the battery pack or cable connections. Once I had things up and running I enjoyed a few weeks of perfect data transmission, with absolutely ZERO dropouts. Then, just as I started to gloat, the dropouts hit me. I was, however, able to fix it in every instance by pushing the connections in. At the same time the dropouts started I got some odd power spikes. That, or I can do 2000 watts seated.

 

Finally, I have to point out that Polar sent me 3 units before I got one that worked perfectly. Now, the one I’m using now is purring along nicely, but this should give you pause when you consider the CS600.

 

Perhaps the next version will have more robust connections and (as suggested on the cyclingforums thread) a rechargeable battery pack you can hide in a seat bag. That would be nice. Polar is working on improving the instruction manuals.

 

So where does that leave us?

 

The Clif Notes version of the CS600 with Power goes like this: It’s a $700 power meter that can work almost as well as ones that cost two or three times more. You don’t have to replace any of your beautiful components, and you can quickly rip it off your bike for an important race. Whether it’s the right power meter for you, then, becomes more of a Myers-Briggs test. Are you a type A rider whose every pedal stroke must be recorded to perfection? Must you compulsively upgrade your components until you have the best of everything? Do you throw things against a wall when they don’t work perfectly right out of the box? If so, stay away. If, however, you like to save a buck, have a bit of MacGuyver in you, think it’s normal to surf the web for tips, and believe that the world will still revolve if your mighty sprint goes undocumented, then you might want to give the CS600 a serious look.

 

Data

Here’s the gearing test. I did two minutes minimum in each gear on rolling terrain. I can’t discern a trend there. 

 

This is the interval test, where I didn’t look at the Powertap display to see if the CS600 could guide me to hitting my target wattage.

 

Here’s some sprints. This is the one workout where the CS600 didn’t come within 3% of the PowerTap for the entire ride. If you look at how it falls short on the sprints you can understand why. Interestingly, during a 19 minute span where there were no sprints, the CS600 read at 97% of the PowerTap. For the sprints, I’d ignore the minimum and average numbers, as grabbing identical 15 second intervals in the two files is pretty impossible.