The SRM Dura Ace Compact Wireless Professional Powermeter is identical in every way to the non-compact version, with only one important change: Instead of using 130mm BCD outer and inner chainrings, the Compact version uses a 130mm BCD outer chainring and a 110mm BCD inner ring. It'll come equipped with a 50t Dura Ace 10-speed outer chainring, and a 34t Shimano R700 inner ring.

If climbing is your cup of tea, arming yourself with a 50x34 makes sense for reasons apparent by running some quick calculations. A 50x11 is a bigger gear than a 53x12, and a 34x23 is smaller than a 39x25. To see the math on a gear inch chart, click here. With a 50x34 you give yourself the flexibility for any terrain: On the flat-to-rolling stuff you can go with a nice, tight cassette cluster such as 11x23 so your jumps in between gears will be subtle. When serious climbing is on the menu you can arm yourself with a 12/25 or 13/26 and feel prepared for the very worst.

The Powercontrol VI that comes standard with this system works on the ANT+ wireless platform. This means that it can communicate with any other ANT+ compatible powermeter. Keep in mind, though, that while it is an altimeter, it is not a GPS. Because of this, you don't track speed and distance via satellite (like you do with a Garmin GPS). Rather, this system comes with a small wireless speed pod manufactured by Suunto. You can mount it either on your fork or on your stays (depending on whether you'd like to read speed from your front or rear wheel). Along with the speed pod, this system will also come with a Suunto heart rate chest strap transmitter. While the wireless SRM transmits power data to the Powercontrol VI via ANT+, speed and heart rate are transmitted via ANT (not ANT+) -- something to keep in mind in case you try to use the pod or the transmitter with another ANT+ device.

Along with the speed pod and transmitter, you'll also receive a small BB-mounted bracket impregnated with a magnet. For those of you familiar with the wired generation of the SRM, you'll note that it looks an awful lot like the head of a sensor cable. The purpose of this magnet is to read cadence, and you must install it -- even if you don't care about cadence. Why? It's because Power = Torque x Cadence, so with no cadence reading you get no power reading.

When you first receive your system, you need go through a quick "pairing" process. This creates an exclusive connection between your Powercontrol VI and your Powermeter, your speed pod, and your heart rate strap. By doing this pairing process, it ensures that you won't pick up your riding partner's signals, and it's also the means by which your Powercontrol reads the slope of your Powermeter. (And if you own two Powermeters on two bikes, but want to use just one Powercontrol, you'll go through this pairing process when you move your Powercontrol from bike to bike -- this ensures that the slope will be correct and your power reading will be optimally accurate.)

The only values you'll need to calibrate manually are the zero offset (this is no different from the wired generation of SRM) and altitude. In terms of the latter, you'll note that there's a GoreTex membrane on the back of your Powercontrol -- this is where barometric pressure is read from for altitude data. But for the sake of absolute accuracy SRM advises that you use Google Earth to determine your exact altitude at the beginning point of your ride, and enter this in your Powercontrol.

Some other notes of interest here: This system is built from the Dura Ace 7800 10-speed generation crankset. It is not the 7900 version, and no 7900 version will be forthcoming due to its design. Also of note is that there is NO cross-compatibility between the SRM wired Professional systems and the wireless Professional systems. The only piece, in fact, that works for both systems is the handlebar clamp. The download cable, the charger, etc, etc are all non-compatible.

When you purchase this system, you'll get the following: The Dura Ace Wireless Powermeter in the cranklength of your choosing (170mm, 172.5mm, or 175mm); a Black Powercontrol VI; an oversized handlebar clamp; a Suunto speed pod; a Suunto heart rate chest transmitter; a BB-mounted cadence magnet; a new generation charger/download cable (like an iPod's, this is a dual-function cable); and an instruction manual.

Nothing is more convincing as you consider purchasing an SRM Powermeter as an understanding of the virtues of training with power. We've done our best to provide this with our article "Power: The Ultimate Training Metric". Reading it will be a worthwhile investment of your time, and please feel free to contact us if we can elaborate on any of the topics brought up there.