2011 Power Meter and Head Unit Review
Part I of II: Power Meters
By Lang Reynolds - 3/2011
A lot has happened in the power meter marketplace since my last review a few years ago. The advent of the ANT+ wireless transmission standard has opened a whole new world of possibilities in head unit selection and some exciting new power meters are on the horizon. Other products have failed and been taken off the market, which is mostly a good thing in those cases.
Power meters are still expensive, but they are also still the most effective tool you can add to your arsenal if you’re looking to improve performance. By providing a complete record of your effort on every ride, you can measure your fitness level in the different physiological systems, determine your strengths and weaknesses in races, and track your overall training stress over longer periods of time. Power meters can also be used prescriptively, to ensure a precise workout and harness correct pacing in time trial and solo efforts.
When shopping for a power meter, it’s best to start by determining your budget. Then, consider the equipment you have – how many and what type of bikes do you want to use with your PM, and what kinds of wheels do you have? No matter which PM you choose, you will have to make sacrifices in equipment choice. Getting a PowerTap locks you into using that wheel (although you can move it between bikes) while getting an SRM lets you use any wheels, but locks you into one bike. Unless PM prices fall dramatically there is just no way around these compromises. So after determining how much money you have to spend, take a little time to decide which equipment sacrifices you are willing to make. Just remember, the data from a power meter (when analyzed correctly) are far more valuable in improving performance than a few grams of weight or some carbon wheel.
One thing that cannot be compromised, however, is accuracy. I hear a lot of people say (regarding certain cheaper PMs that are not accurate) “well, even if it’s not accurate, as long as it is consistent it should be fine.” First of all, absolute accuracy is very important because it allows you to make comparisons across individuals, and also within an individual’s data set over time. If you buy one PM today and another one two years down the road, you need to be able to compare your data from your first PM with that of your new one.
Secondly, and more importantly, these PMs that are not accurate are also not consistent. This is very important because changes in fitness over the course of a season can sometimes be very small, on the order of just a few percent or sometimes even less than that. If your power meter is not sufficiently accurate, it is impossible to determine whether the changes you are seeing in the data are due to changes in your fitness, or just the capriciousness of your PM. If you don’t have confidence in your data, then the PM is not an effective tool because you have no concrete connection between the training stress you’ve applied and the changes in fitness you are attempting to measuring. An inaccurate PM, therefore, is a useless PM. PMs are not like race wheels or bike frames, where you can buy a less expensive product that delivers a large percentage of the performance of the higher-end model for a fraction of the cost. In the world of PMs, there is an accuracy threshold below which the products are not worth buying. Unlike a lot of other publications in the cycling industry, I’ve actually performed my own extensive testing on many of the products in the marketplace, and I’m not afraid to point out the ones which have failed these tests.
Without further ado, here is a rundown of the PMs now available:
PowerTap is still the industry leader in PMs as they continue to provide the best combination of accuracy, affordability, reliability, ease of use, and user serviceability. At +/-1.5%, PowerTaps remain the most accurate factory-rated PM on the market. CycleOps hasn’t changed too much about the PowerTap line since I last wrote, but they have updated all of their wireless models to the ANT+ standard for use with the next generation of head units such as Garmin GPS computers. They’ve made their top of the line hub lighter and added ceramic bearings, and they’ve also introduced more affordable low- and mid-range models. At $600, the wired Comp model is the most affordable PM on the market and the go-to choice for the cyclist on the budget.
Featureing great realiability, PowerTaps also have user-serviceable batteries; both hub and head unit batteries can be changed in minutes for a cost of about $5.
PowerTap hubs are available in road, track and MTB configuration. Here’s a quick breakdown of all the PowerTap models and the differences between them (Prices are for hub only):
ANT+ Wireless Hubs:
SLC+ $1849, 15mm Alloy Axle + Freehub Body, Carbon Hub Shell, Ceramic Bearings 402g
SL+ $1349, 15mm Alloy Axle + Freehub Body, Carbon Hub Shell, 412g
Pro+ $949 , 15mm Alloy Axle + Freehub Body, Alloy Hub Shell, 466g <--- Best Wireless Value
Elite+ $849, 15mm Steel Axle + Freehub Body, Alloy Hub Shell, 583g
Comp $599, 15mm Steel Axle + Freehub Body, Carbon Hub Shell, 576g <--- Best Overall Value
Equipment tradeoffs: The PowerTap locks you into one wheel, but by getting a PowerTap laced to a rim strong enough for training but light enough for racing, such as a carbon clincher, you can have a wheel that does it all and won’t hold you back on race day. Add a WheelBuilder.com wheel cover and you also have a disc wheel for TTs that tests faster in the wind tunnel than many disc wheels .
Buy a PowerTap if: You want to use a PM on multiple different bikes.
Since our last edition, SRM has also gone wireless with their crank-based power meter, joining the ranks of ANT+ transmitted PMs. The most expensive PM on the market, SRM is in the same class of accuracy as the PowerTap, rated at +/-2%. With ANT+ data transmission, you can use any ANT+ head unit including SRM’s own PowerControl 7 or third-party units such as a Garmin or even the CycleOps Joule 2.0.
SRMs are accurate and reliable, but they are also the most expensive PMs on the market and have a few small drawbacks. One annoying fact is that most of them come from the factory calibrated with the wrong slope value, and must be user-calibrated after installation to give truly accurate readings. The slope value must also be re-calibrated when changing the chaingrings. They are also not user-serviceable and must be sent back to the SRM Service Center in Colorado when the batteries die, for a hefty servicing fee of $100+.
The SRM is also available in Road (Standard or Compact), Track and MTB configurations. For road cranks, it is available built into a variety of popular crank choices (SRAM, FSA, Shimano, Cannondale and Specialized) and ranges from $1895-$2945 for the crank only
Equipment Tradeoffs: As a crank-based PM, the SRM locks you into using just one bike, unless you are sufficiently mechanically competent and confident to switch cranks between bikes frequently. For some crank varieties (such as Cannondale) this is easier than others.
Buy an SRM if: You have plenty of money to spend and only one bike you want to use your PM with, or if you are comfortable enough mechanically to frequently switch cranks between bikes.
One of the newer PMs on the marketplace, Quarq is a crank-based unit like the SRM, but is much less expensive. With ANT+ wireless transmission, the Quarq is also compatible with all ANT+ head units. While factory rated with +/-2% accuracy my own research has shown multiple Quarq units to have accuracy no better than 5%, which is not sufficient for use as a PM. Quarq has insisted it has remedied the accuracy issue but I have not been able to re-test any units since the improvements were announced. Additionally, because the Quarq auto-zeroes its torque reading when the crank is pedaled backward, some of our clients have had issues with their Quarqs auto-zeroing while in the start house for a TT, leading to inaccurate power readings during the TT.
While it is a promising product, until Quarq adequately resolves these accuracy issues I do not recommend purchasing one.
Garmin “Vector” Pedal-based PM
Announced to much fanfare in late 2009, the then-MetriGear Vector was to be the first pedal-based power meter. This product created a lot of buzz because, if sufficiently affordable, a pedal-based PM could potentially avoid many of the equipment compromises demanded by other PMs currently on the market. However, publicized release dates of Q1` and Q2 2010 came and went without so much as a public working prototype and despite being purchased by Garmin in late 2010, the Vector is still vaporware. While its purchase by Garmin suggests a viable product is actually in the works, the length of time the Vector has been in production and the lack of any pre-release prototypes has convinced me that the Vector is at least a year from reaching the marketplace, if not more.
Additionally given the track record of numerous bugs in the first batches of other PMs, even if the Vector is released in the next year I wouldn’t recommend buying one until after the first production run has been in the marketplace for a period of time. Therefore, my advice to those waiting on the Vector is: stop waiting. Buy an SRM or a PowerTap now, start reaping the benefits of using a PM, and in two years when the Vector has been out for a while and all the kinks have been worked out, THEN think about getting one.
Polar Pedal-Based PM
Basically the same thing goes for the Polar pedal-based PM as for the Vector. This thing is a long way from the market and it does not make sense to wait for it when there are solid products already on the market. I hope to be writing about this product in a couple years’ time after it comes out, but until then get a real PM that already exists.
The iBike calculates power by measuring all of the forces acting against the motion of a cyclist: aerodynamic drag, gravity, and rolling resistance. Unfortunately there are so many measurements necessary to make these calculations that the iBike is not accurate enough (except on hills) to be considered a true power meter. Additionally the calibrations necessary before initially using the iBike, and those necessary before each ride are so numerous and cumbersome that they make using one an exercise in frustration. Lastly, the user-interface is extremely non-intuitive and very difficult to use.
However, because the iBike can now function as an ANT+ head unit for a regular PM, it can act as a very useful training tool. When paired with a regular PM, the iBike’s wind-measuring sensors give it the ability to calculate aerodynamic drag, essentially turning your bike into a portable (and very cheap compared to the real thing) wind tunnel. Using the iBike as a wind tunnel, you can test time trial positions and equipment, and also determine your most aerodynamic position on your road bike.
I owe iBike an apology: when I wrote my first PM review I mentioned some customer service issues one of our clients had with the company. After getting some more information, it’s become apparent that iBike provides some of the best customer service in the industry and is extremely responsive in resolving any issues their customers have.
Buy an iBike if: You already have an ANT+ PM and would like to perform aerodynamic testing
Ergomo is now out of business, which is great because their PMs were not accurate, due to the fact that they only measured power from one crankarm. If you come across one of these in the secondary market (i.e. eBay, a friend selling one, etc.) run far away and don’t even think about buying it.
Stay tuned for Part II: Head Units
Questions about Power Meters or Training with Power? Contact Coach Lang at Lang@cycleu.com.
Cycle U has Power Tap wheels for demo or purchase, call or stop on in.