Power meters to the people

After Stage 8 of last year’s Tour de France, in which Sky Pro Cycling methodically shelled the entire peloton, RadioShack-Nissan rider Chris Horner was interviewed by Frankie Andreu for a post-mortem on what happened that day. Horner said he had pushed more than 300 watts just to keep up on the final climb. The mention of power and watts passed without followup from Andreu for the general audience. It seems even the casual fan knows, at the very least, watts are a common currency.

To review: a watt is a measure of the rate of work you do to propel you and your bike. You can use other metrics to gauge your ability, such as speed, but it’s affected by wind and gradient. You can go slower on a windy day while working much harder. Heart rate is a good indicator of how hard you are working, but is affected by many factors, such as your level of fitness, level of fatigue and even the temperature. One too many espressos at the mid-ride coffee stop can put your heart rate through the roof.

Power, on the other hand, is a consistent measure of the work done by you. The 200 watts you did today are the same as the 200 watts you did three months ago regardless of your heart rate or the conditions in which you were riding. Power is an objective measure of your effort and allows for accurate comparison of your workouts over time. Tracking and comparing of your adaptation to training, along with hard work, are some of the keys to long-term improvement.

Power meters are not just for the pros. For anyone who is interested in improving, whether racing at an amateur level, training for a gran fondo or even a cycling holiday, a power meter is arguably the best investment one can make. And it is an investment as its price starts at roughly $1,000. Furthermore, if you want to ride better this summer, you’ll want to start training with power now.

For this review, I took five of the most common power meters and tested them from May to the end of November. In each case, I zeroed the power meter manually at startup. I also ran several power meters on the same bike simultaneously whenever possible.

::GEARBOX
SRM Dura-Ace 7900 Compatible
US $3.145.00
41030

SRM is the first bicycle power meter and has become a benchmark for others. Located in the crankarm spider, the SRM uses eight strain gauges to measure torque and cadence to calculate power readings.

The competent home mechanic will find the installation has a medium level of difficulty, but is straightforward. You will need to be comfortable installing cranks, as well as adjusting derailleur cables. Once installed, the SRM pairs easily with the company’s own PowerControl 7 head unit, as well as any other ANT+-compatible units. While this meter worked with a set of Shimano Dura-Ace 7900 cranks, SRM has systems that work with SRAM, Campagnolo and aftermarket options, such as FSA and Rotor.

The battery of the SRM is rated for 1,400 hours, nearly two years for the average rider. Unlike the other units in this review, you cannot replace the battery yourself. Once the cell is drained, you must send the whole unit back to SRM, who will replace the battery and calibrate the unit.

The SRM meter I tested operated flawlessly in all weather conditions; there wasn’t a single signal dropped during the test period. The measured wattage was inline with the other units within the test. The SRM does not offer left-side/rightside power readings; it adds 80 g to the regular Dura-Ace 7900 crankset, a fairly minimal penalty.

The SRM comes with SRMWin software, which is used to configure and download data from the PowerControl 7 head unit. The software is very basic, showing average watts, heart rate, speed, distance and cadence within each file. You can also divide your file into segments, but that’s it. There are no training stress scores (TSS), normalized power or any other power metrics, nor are there any long-term reporting functions. You will need to budget for additional software, such as WKO+ or Golden Cheetah. A pay-as-you-go TrainingPeaks account is another option.

With so many bottom bracket standards, you run the risk of future incompatibility problems with crank-based systems, an issue for the SRM, as well as Quarq and Power2Max. If you upgrade your bike or frame every few years, you might run into trouble when you try to bring the power meter over.

SRM’s units are highly accurate and reliable, with a minimal weight penalty. It’s no wonder many professionals choose it. However, it also comes with a professional price tag. The unit’s high cost and that its battery must be replaced by SRM itself means this power meter is for riders with a team mechanic or who want to look professional. Get it if you already have the Pinarello Dogma and Team Sky livery.

::GEARBOX
CycleOps PowerTap G3
$1,600(alloy wheelset)
41031

Available since 2001, the PowerTap by CycleOps is probably the most popular power meter out there. The meter is in a rear-wheel hub. Eight strain gauges inside what CycleOps calls the Torque Tube generate a power reading from the wheel’s rotation.

PowerTap is as close to plug and play as it gets for power meters. Swap your rear wheel with the PowerTap wheel, pair it with the head unit of your choice and done. This simple installation make it very easy to transfer the meter between bikes, such as between your road and cyclocross bike (with the appropriate tire swap). It’s perfect for riders with only a little mechanical know-how or those with multiple bikes and the budget for only one power meter.

I have ridden with PowerTap wheels for four years, through sub-zero winter temperatures and summer downpours. They have been accurate and dependable throughout. However, the latest G3 model shows marked improvements that address nearly all of the shortcomings of previous versions.

The most significant change is the G3’s size and weight. With the hubs at 325 g, the new G3 is more than 100 g lighter than my older Pro+ version. The G3 sits at the centre of a noticeably lighter wheel with an increased stiffness due to smaller and wider hub flanges. Normally, during our office’s weekly morning hill repeats, about two thirds of the way up the climb, I will need to get out of the saddle. With my old wheel, I would get just a bit of brake rub as I wrenched the bike from side to side in a desperate bid to maintain contact with the group. With the new G3, there wasn’t any of that. It didn’t make me any faster or help me close gaps, but it did help me dig deeper psychologically since I didn’t have wheel rub as an excuse.

CycleOps also rearranged the innards of the hub so that all of the electronics, the parts most likely to fail first, now sit on the non-drive-side hubcap. If something goes wrong, simply unscrew the cap that covers the electronic package and send it back for service: no need to send the entire wheel.

The CycleOps PowerAgent software is also the best of the free analysis software supplied with the power meters. It allows you break a ride file into multiple segments with detailed breakdowns of peak power, TSS, normalized power and functional threshold power. It also has the usual array of average and maximum speed, distance and heart rate. A beginner can get pretty far with this level of analysis before needing more sophisticated software.

These improvements make the G3 a noticeably better offering compared to its predecessors. It’s only downside is that you are tied to one wheelset when you want power information. This arrangement may be a deal breaker for the cyclist who already has, or has access to, a quiver of hoops. For those without this problem, a Powertap G3 built into the latest generation of deep-profile carbon clincher rims will come very close to being a do-it-all wheelset with the bonus of power.

::GEARBOX
Polar/Look Keo Power Pedals
$2,300
41028

Polar and Look’s collaboration has created the first, and so far, only power meter built into pedals. By putting eight strain gauges into each pedal spindle, the companies have made a power meter that’s light, easy to install and easy to move from bike to bike. These units also provide left- and right-leg power readings and pedal force analysis. Since each pedal measures power independently from the other, the data sent to the Polar head unit can be displayed as the total power, as well as the left/right split. A magnet is built into the bottom of one of the pedals measures the cadence.

Installing the Look/Polar system is no more difficult than putting in a regular pair of pedals. But you should give yourself extra time for the first installation as precision is required. The spindles must not protrude beyond the inside edge of each crank. (Spacers are provided for this setup.) There is a notch on the threaded end of each spindle that must be aligned precisely, perpendicular to the length of each crankarm. Look provides a tool to help with this process, but it is still a finicky affair. In fact, I received funny readings on my first ride compared to the SRM and PowerTap I was running at the same time. A check revealed that I had the alignment of the notches slightly off, which skewed the readings.

Once that issue was fixed, I had consistent and accurate readings from the pedals, which always tracked closely with the data from the SRM and PowerTap. Post-ride analysis showed averages always between 3-7 watts, well within the ±2 per cent margin of error for all these devices. Look/Polar has built an automatic check of all systems during the startup of the device – essentially zeroing the unit – a good feature of any power meter. The left and right power readings were interesting. The reading varied widely for me and other testers depending on cadence, effort and fatigue levels. The jury is still out on the usefulness of this data.

One blip I had from the Look/Polar pedal was for the maximum power. On a few rides, it gave me a much higher peak one-second power compared to the SRM and PowerTap. How high? It said I was briefly in Mark Cavendish territory: flattering for the ego, but simply impossible. This is something to keep in mind if you are training for sprints, but not something that would affect general training.

Polar is behind the software and head unit, which means the unit uses Polar’s WIND protocol rather than ANT+, limiting computer options to Polar’s CS600x (tested) and CS500. The CS600x is well designed as a speed/heart-rate/cadence monitor. However, it is a legacy unit pressed into service and lacks important power metrics. The only metric that can be displayed is the instant and left-and-right power. The unit cannot show averages, interval modes, TSS or normalized power. Also, it doesn’t show 3-5 second rolling averages. The included software, Polar ProTrainer 5, is limited in its post-ride analysis; however, it is relatively easy to export files into another program, such as WKO+, for a deeper examination.

The good news is that Polar has promised upgrades (appearing soon) to the ProTrainer 5 software for better power analysis. Both Look and Polar have said that future Keo Power Pedals will support the Bluetooth low-energy (BTL E) standard, which means new head units, presumably with richer power features, are in the works. This development also opens up the possibility of third-party head units, such as the forthcoming Wahoo RFL KT bike computer or your iPhone. Look also plans to make BTL E retrofittable for current units.

The Look/Polar Keo Power pedal is a very good piece of hardware with a few software limitations. However, it is the only power meter that will give a genuine left-and-right power split. It also shows much promise with the upcoming BTL E implementation and additional head-unit compatibility.

::GEARBOX
Power2Max Rotor 3D
$1,390
41029

Power2Max is a new power meter from Germany and the least expensive of the crank-based options. The ANT+-compatible device has four strain gauges in the right crank-arm spider to measure torque and an internal accelerometer that takes care of cadence. This arrangement means there’s no need to add a magnet during setup, which simplifies installation. Once you (or your mechanic) have installed the appropriate bottom bracket and crankset, the unit is ready to pair with the ANT+-compatible head unit of your choice.

Early models of the Power2Max were overly sensitive to temperature changes, which led to anomalous power readings, especially if you took your bike from inside a warm house to the cold outdoors. I never experienced these problems, but I was careful to zero the power meter each time the bike had been out or before each ride. However, Power2Max has addressed the problem. Since September 2012, all units have been equipped with a temperature sensor. Power2Max even sent me one of the new units halfway through the test period to ensure I had the latest hardware. If you already have a Power2Max, you can can send the unit back for a hardware upgrade for a fee. Your unit will also receive a software update so that it can extrapolate left and right power to head units that support that function.

The Power2Max was the most user-friendly of the crankbased systems. Since it didn’t need a magnet, I found it easy to swap between test bikes. There’s no need for recalibration when changing chainrings. Finally, you can replace the battery yourself easily.

The unit’s simplicity brings some limitations. You cannot calibrate the system as Power2Max says there is no need to. However, if you discover a discrepancy, you cannot reset the machine yourself. Instead, you’ll have to send the unit back to the manufacturer. The Power2Max is also rather bulky compared to the other units in this test, weighing about 200 g more than a regular Rotor 3D spider. Included in that weight is some excellent waterproofing. At present, there are limited crank options for Power2Max in North America: the only compatible crankarms are Rotor, Lightening and SRAM S900. The unit doesn’t come with software, so you’ll have to get WKO+ or Golden Cheetah.

In short, Power2Max is an excellent option for those who want the user friendliness of a PowerTap in a crank-based package.

::GEARBOX
Quarq SRAM S975
$2,000
41033
The Quarq sits between the Power2Max and SRM in terms of price. Like the other two meters, the Quarq measures power via strain gauges in the spider of the right crankarm. Installing the Quarq is straightforward, the same as a normal crank and bottom-bracket installation. Like the SRM, the Quarq requires the installation of a magnet to measure cadence. However, Quarq provides a handy bottom-bracket ring mount, so you don’t need to mess with cable guides and derailleur adjustments. There are a range of crankset options that include SRAM, Rotor and Cannondale. But there are no Shimano or Campagnolo Quarq cranksets available.

Since the Quarq is ANT+ compatible, it paired easily with all of the head units used in the test. It provided reliable data with very few dropped signals. It also tracked very closely with the power readings from the PowerTap, usually within a few watts. When the bike is stationary, you can zero the Quarq manually with an appropriate head unit (Garmin or Joule). You can zero on the fly by pedalling backward with 4-5 revolutions while coasting. I didn’t need to replace the battery during the test (the standard battery is rated for 400 hours), but the battery compartment of the Quarq was the most accessible of the units tested – no disassembly or tools required.

One issue with the Quarq is the need to recalibrate whenever new chainrings are installed, such as replacing a worn chainring or installing the power meter on your ‘cross rig. However, you’d have to send the unit back to Quarq for calibration, which is an inconvenience. Fortunately, Quarq has provided a workaround. With an iPhone and a Wahoo ANT+ adaptor, you can download the free Qalvin app from Quarq and do the calibration yourself. The process is not difficult, and the app will walk you through it step by step. But it will take some time and you’ll have to have some accurate known weights on hand.

While the Qalvin app is not actually part of the power meter, it is one of the most interesting features of the Quarq. Not only does it allow you to calibrate the power meter, it lets you check your battery level and update firmware wirelessly. It’s a full diagnostic tool that will be useful to any Quarq owner. Beyond Qalvin however, Quarq does not provide any software for post-ride data analysis. You’ll need to rely on third party software.

Quarq carries similar weight penalty as the Power2Max, approximately 200 g depending on the model. The unit is very SRAM-centric, which will turn off the Shimano and Campy riders. Quarq’s price is similar to the SRM unit. While the Quarq performed excellently in the test, the Power2Max is a better choice for those on a budget. But the advanced user who is able to use the added features offered by the Qalvin app should definitely consider the Quarq.

Displays of Power

::GEARBOX
SRM PowerControl 7
US $900*
41034
Designed for SRM’s power meters, the PowerControl 7 offers a clear display with all of the key training metrics available. It also boasts the biggest memory and longest battery life of the units tested. *(includes speed/distance sensor and heart-rate monitor strap)

::GEARBOX
Garmin Edge 500
$385
41204
The smaller of the two cycling-specific units from Garmin, the Edge 500’s display can be easily configured to show an impressive variety of metrics, including TSS, normalized power, instant and average watts, in addition to the usual array of speed/distance information.

::GEARBOX
CycleOps Joule GPS
$280
41036

With this update to the Joule, CycleOps has added GPS functionality. The big draw is the clear display and the ability to highlight a primary field (such as watts) and see related data fields (average and maximum power).

::GEARBOX
Timex Cycle Trainer 2.0
$275
41035
Straying from their usual watch design, Timex has created the new Cycle Trainer 2.0. It has a magnetic compass, a feature unique to it among the units tested.

::GEARBOX
Polar CS600x
$400
41191

One of only two units compatible with the Polar/Look Keo Power Pedal, the CS600x is our preferred model owing to its smaller size. In power mode, the CS600x will display speed, cadence, as well as left and right power.