Is it Time to Buy a Power Meter?

Is it Time to Buy a Power Meter?

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The pre-release of the StageOnePower power metre is a sign that power data is starting to become available to the Semi-Pro for a realistic price. This coincides with my hunt for a complete data solution for my new training regime. Join me as I break down power and offer my recommendations for the ultimate bike data setup for today and the future.


Is it Time to Buy a Power Meter?


Like the evolution of our phones, bike computers are increasingly getting smarter. Which not only means interpreting the data is becoming more complex, but the way we collect data is becoming an entire industry in itself. Sifting through proprietary wireless sensor network technology (I know right!) and wireless radio technology, combining them with head units, cadence sensors, power metres…you get the point.


Last time I had a coach I turned down the option of training with power. I thought forking out $300 on a Garmin Edge 305 was enough at the time. While it was a massive leap forward when combined with Sporttracks, I was with that coach for 2 years and at times thought about what if I had gone the other way. I wouldn’t say my campaign was a disappointment but I didn’t achieve some of my main goals.


Now I realise a lot of factors go into achieving cycling goals, but at times I felt that I couldn’t hit my magic number in training (the HR number that represents my target range for the racing I was doing) and a lot of my sessions were wasted because of it. Something inside me believes that following an absolute measure of output would have been a better target and gauge of my progress.


This has a lot to do with my personality, and if you are anything like me, you spend your life trying to quantify the world around you. Power metres seem to be the best available way to do that in this context. I approach my training quite systematically and a power metre looks like the pinnacle of that approach. So now that I’m about to embark on a new cycling challenge, more to come about that one, and the prices are coming down, I’m considering buying a power metre, and everything that goes with it. Therefore I’m revisiting the whole idea of power. This is my process of the why, how and what of riding data with a heavy focus on power. At the end of the Nuts & Bolts I’m going to give two options I’m considering today, and one you can buy in January.


Watts. The Best Way to Measure Training ROI. Power is the most tangible form of measurement for cycling improvement.


How is Power Measured on a Bike?


Each power meter has a different way to measure forces and, because of patents, each has chosen to measure them in a different “location.”


Most power meters measure the forces somewhere along the drivetrain: working from the back to the front, the PowerTap measures at the rear hub, the older Polar systems measured along the chain, the Quarq/SRAM, SRM, StageOne and Power2Max measure at the left or right crank or spider, the new Look/Polar and Garmin Vector  (thus far, announced but unreleased) measured at the pedal spindle, the (announced but unreleased) Brim Brothers measures at the shoe cleat, and the deceased Ergomo measured at the bottom bracket. The iBike measures in a completely different way discussed below.


One consequence of measuring at various points along the drivetrain is that drivetrain losses will (or won’t) be accounted for to a different degree; for example, a PowerTap will usually read lower than an SRM since one is “upstream” of most drivetrain losses while the other is “downstream.” This difference is more of a definitional issue than a strict “accuracy” issue (in the sense of, “is gross income or net income a more ‘accurate’ measure of income?” Unless you have a specific use in mind, it’s hard to say which is more “accurate”).


The PowerTap, Quarq, Power2Max, StageOne and SRM use strain gauges, which are small thin foil strips whose electrical conductance and resistance varies as they are deformed. Strain gauges are used in lots of applications (like, bridges) and their properties are well-understood. In general, strain gauges are combined in a “rosette” or “Wheatstone bridge” in order to produce more accuracy and precision (more strain gages usually produce better results), and, when operating properly the Power Tap, Quarq, and SRM are usually accurate to within a couple percent (and, just as importantly, with high precision); this has been verified both statically (using known weights hung from the crank) and also dynamically (using a large powered rolling drum in a lab).


The forces are then combined with a measurement of angular velocity or speed to get power. A virtue of strain gages is that the change in resistance can be measured even when the device is stationary so the cyclist can measure the accuracy of the strain-gage-based power meters at home by hanging weights of a known mass from the crank. A common problem with the strain gage approach, however, is that they can be sensitive to changes in temperature and so need to be “re-zeroed” prior to (and sometimes, during) rides. The new Power2Max (and the old discontinued SRM “Amateur” model) uses fewer strain gages than the current PowerTap, Quarq/SRAM, or SRM models.


The unreleased Garmin Vector and Brim Brothers pedal or pedal cleat power meters are rumoured to use piezoelectric sensors and solid state accelerometers rather than foil strain gauges but until they reach the market all claims about accuracy or precision should be taken with grains of salt. An interesting problem in the design of a pedal- or cleat-based power meter is that the direction of force and the position of the pedal spindle must be known: for example, if you add downward force at the bottom of the pedal stroke, that is wasted force since it does not aid in moving the crank in the correct direction; likewise, if you press down (however slightly) on the upstroke, that will cancel out some of the force exerted by the other leg on its downstroke. Keeping track of the various force vectors is, therefore, the key to getting reliable accuracy and precision.


The Look/Polar power meter uses strain gauges arrayed along the pedal spindle, and each pedal must be carefully installed so the pedals know which direction the forces are being applied — a special tool is supplied with the pedals to help with the orientation. To simplify the conversion of measured forces to torque values, the Look/Polar pedal allows the use of only four different crank lengths: 170mm, 172.5mm, 175mm, and 177.5mm. Cranks shorter than 170mm are currently not supported. One pedal is the “master” and the other is the “slave”; the slave pedal transmits information to the master which then bundles data from both pedals and forwards it to the head unit.


At the moment, the Look/Polar pedal uses its own transmission protocol and no other manufacturer has yet signed on to provide compatible head units. Early reports on the new Look pedals confirm that the orientation of the pedals is critical: because the spindle of a pedal is small, a small absolute error in alignment can be a large relative error in its angular orientation.


In general, all of the commercially released power meters have been accurate (and sometimes precise) when newly-adjusted and performing under ideal conditions. However, conditions are not always ideal and parts get damaged, dirty, and deteriorate. If accuracy and precision are important then the “design” accuracy (whether based on strain gauges, optical sensors, magnetic sensors, or wind speed sensors) is only half the battle: equally important is the ability to verify a power meter at home so you can tell when they’re off.


Best Place to Measure Power?


Honestly, there is no best place to measure power. The best really comes down to being the best overall solution. As long as they produce an accurate reading, which has been tested, then there are more important factors to consider when choosing a power metre. These are mostly to do with the type of bike you own, do you have race wheels, a second bike etc…oh and the cost.


Why is Power Data so Expensive?


Of all the available data; speed, cadence, heart rate and GPS, power is the most expensive. It’s expensive because power meters use highly-sensitive strain gauges and require careful calibration. A lot of design has to go into working out how to overcome external factors like temperature changes while at the same time producing a light and weather proof system. Obviously, something Garmin hasn’t worked out yet.


Best Power Metre Available Today


SRM. Hands down. It has the longest history of all the power metres so you know they have their shit sorted. If I read ‘Gold Standard’ one more time though! So let’s move past best and into something that is going to be more affordable for the Semi-Pro. I only believe there are 2 options, they happen to be the cheapest way to get power and one of them is not even released yet.


The Best for the Rest – PowerTap & StageOne


StageOne is a game changer. At $699-$899 USD the cost is an appealing attribute. By adding a $300 head unit the StageOne breaks the mythical $1000 price point. A small strain gauge and accelerometer measure the direct force applied by being bonded onto any regular left crankarm and then sends information to the head unit. The crank arm must be purchased with the unit already attached. Then all you need to do is attach the crank arm and calibrate it with your head unit. Accuracy is said to be the same as the big players and it’s light, only adding 20g to your crank arm weight.


The price is low, however, it’s not quite as low as you think. The cheapest PowerTap’s aren’t much higher. The difference though is that for riders that have multiple wheelsets, this allows them to choose whatever wheels they want without worrying about the hub in it.


The big question is does it work. The lack of any users and feedback from the community is the unknown factor. Relying on the release date is also a gamble at this point. New companies will have bugs to workout, using the Vector pedals as an example, Garmin is a smart and large company and they are still being delayed.


It’s something to think about considering you could buy a proven product today. The closest rival at the less expensive end of the market is Cyclops’s PowerTap, which has been around for over 10 years and has a solid reputation. Things to remember here are all models but the G3 will be phased out over time. This is important because there is $350 difference between the PRO model and the G3 at the time of recording.

The Ultimate Bike Data Setup?


Sports devices have a long lifecycle so it would be good to ‘recycle’ some parts when upgrading or adding to your data capabilities. Personally, I am going to transfer my Garmin Edge 305 kit into a new tech kit.


Now I’ve split these into two main categories. Non-smartphone and smartphone. The difference for you will depend on your situation, for example whether you own a iPhone 4S already, whether you train and race with a computer etc. For me, I won’t be racing anytime soon but I am going to be training for a sportive, and want the flexibility and convenience that training with a smartphone will provide. If you’re a hardcore racer, then a phone just won’t cut it, especially if you race something like XC mountain biking. The other element is today versus tomorrow, meaning a setup you can order right after this podcast or one you will have to wait for, probably January sometime. OK, here’s my breakdown and options that I am considering.


1. Today – Non-smartphone

  1. Garmin 500: $300
  2. Garmin GSC-10: $35 (Already Own)
  3. Garmin HR Strap: $40 (Already Own)
  4. Power Metre: Road Powertap G3: $1360 or MTB 29er Powertap: $1250


Total Road: $1660

Total MTB: $1550


2. Today: Smartphone

  1. iPhone 3GS (Already Own)
  2. Garmin GSC-10: $35 (Already Own)
  3. Garmin HR Strap: $40 (Already Own)
  4. Wahoo iPhone Key: $50
  5. Power Metre: Road Powertap G3: $1360 or MTB 29er Powertap: $1250

Total Road: $1410

Total MTB: $1300


3. Tomorrow: Non-Smartphone

  1. Garmin 500: $300
  2. Garmin GSC-10: $35 (Already Own)
  3. Garmin HR Strap: $40 (Already Own)
  4. Power Metre: StageOne – Shimano Ultegra: $799


Total: $1100


4. Tomorrow – Smartphone

  1. iPhone 4S: $650
  2. Blue SC: $60
  3. 4iiii’s Viiiiva Bluetooth Smart and ANT+ Consolidator Heart Rate Strap: $100
  4. Wahoo RFLKT ANT+ & Bluetooth Smart: $120
  5. Power Metre: StageOne – Shimano Ultegra: $799


Total: $1729


Its clear prices have come down, and the flexibility of iPhone apps has increased, but the cost is still really high. I just sold a bike for $1500, turning around and spending this on a power metre still sounds crazy to me. It’s interesting to me that I even with the introduction of the StageOne power metre, I would only save $300 if I bought it for my situation.


This does not even consider the gamble I mentioned earlier about buying a product that is unproven in real life yet. I’m actually still unconvinced. Sure the price is still half of what it was the last time I looked into this around 2008. So, for now, I’m going to hold off until I work out the bike I’m going to buy, then figure out my budget.


Tech, Hacks & Products Section


Another type of power, willpower. Getting out and doing the work takes self-control and focus, as does doing great work. I think it’s important part of the brain to conquer in setting and achieving cycling goals. I’m getting ready to gear up so i went hunting for some literature to keep me on task and I found these two great books. I don’t want to come across all preachy about this stuff so I have the titles and descriptions on the post page of this show. Check them out if this stuff floats your boat.


Two book recommendations.


Willpower: Rediscovering the Greatest Human Strength by Roy F. Baumeister & John Tierney


Willpower shares lessons on how to focus our strength, resist temptation and redirect our lives. It shows readers how to be realistic when setting goals, monitor their progress, and how to keep faith when they falter. By blending practical wisdom with the best of recent research science, Willpower makes it clear that whatever we seek—from happiness to good health to financial security—we won’t reach our goals without first learning to harness self-control.


The Power of Habit: Why We Do What We Do in Life and Business by Charles Duhigg


In The Power of Habit, award-winning New York Times business reporter Charles Duhigg takes us to the thrilling edge of scientific discoveries that explain why habits exist and how they can be changed. With penetrating intelligence and an ability to distil vast amounts of information into engrossing narratives, Duhigg brings to life a whole new understanding of human nature and its potential for transformation.


Along the way, we learn why some people and companies struggle to change, despite years of trying, while others seem to remake themselves overnight. We visit laboratories where neuroscientists explore how habits work and where, exactly, they reside in our brains. We discover how the right habits were crucial to the success of Olympic swimmer Michael Phelps, Starbucks CEO Howard Schultz, and civil-rights hero Martin Luther King, Jr. We go inside Procter & Gamble, Target superstores, Rick Warren’s Saddleback Church, NFL locker rooms, and the nation’s largest hospitals and see how implementing so-called keystone habits can earn billions and mean the difference between failure and success, life and death.


At its core, The Power of Habit contains an exhilarating argument: The key to exercising regularly, losing weight, raising exceptional children, becoming more productive, building revolutionary companies and social movements, and achieving success is understanding how habits work.


Habits aren’t destiny. As Charles Duhigg shows, by harnessing this new science, we can transform our businesses, our communities, and our lives.





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2 Responses to Is it Time to Buy a Power Meter?

  1. […] My show, Semi-Pro Cycling, is a podcast that analyses and addresses cycling issues from the riders’ perspective. As part of the show, I revisited the idea of buying a power meter for my training. This post is a summary of those findings. For a full analysis and recommendations on the ultimate data setup for your bike, check out Episode #17 – Is it time to buy a power meter? […]

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