Power players

With new power metres hitting the market, is now the time to start watching your watts, or is there more to come?

These days we live in a digitally obsessed world, thriving on measuring and assessing almost every aspect of our daily existence. Thanks to a boom in available portable technology, cyclists are now logging more data during a few hours on the roads than an F1 team during track testing a few years ago. Average speeds and heart rates won’t cut it in the post-ride cafe chat nowadays. If you want to hold your own you’ll need to be packing more stats than that, and the one you need right at the top of your personal Top Trumps is ‘power’.

It’s a situation that benefits both sides of the market: gadget-loving cyclists can find countless ways to fill their heads and handlebar displays with numbers; while the manufacturers are rubbing their hands with glee as they can cash in on ways to give the data junkies their fix. But for anyone salivating at the chance to spank the credit card on more techno-wizardry, there is still a pertinent question to ask: ‘Why do I need a power meter?’ 

Game changer

The ability to measure a cyclist’s power output outside the confines of a laboratory has undeniably been the most significant development for observing the intensity of cycling since the advent of the heart rate monitor. It’s now the most important metric for determining performance potential and training effectiveness.

PowerTap’s Jesse Bartholomew says, ‘Ten years ago power output was considered far too technical for most, whereas now it’s accepted that even the most basic goals can be helped along with the proper use of a power meter.’

Stages Cycling’s Matt Pacocha has a similar opinion, saying, ‘Power meters are now being integrated as performance-oriented technologies, and they are accepted, just like electronic shifting.’ As such, watts have become the new currency for anyone serious about their cycling, but measuring power is not as new a concept as its recent boom in popularity might suggest.

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Go back as far as the 1980s and you’ll see Greg LeMond keeping an eye on his wattage with a set of SRM cranks (the first commercially available portable system). The SRM crank-based system has certainly stood the test of time, and two decades on it is still considered the industry gold standard. What has changed, however, is the number of smaller, simpler power meters available.

Largely due to the continual miniturisation of electrical components, power meters have become more compact, which is great news for the end user, as they are now neater and lighter than ever. As Garmin and Polar have proved, it’s now possible to fit a power-measuring device inside a pedal. This makes the usability of power meters more attractive to those who don’t want the hassle of fitting a new crankset to their bike. What hasn’t really changed, however, is price.

The cost of power

Regardless of the model, power meters are still expensive commodities, which is why the market has yet to be flooded with affordable products. But where does the bulk of the cost lie? Stages’ Pacocha says, ‘Much of the cost isn’t in the components themselves but actually comes from the design IP [intellectual property] and programming know-how that allows us to pull the relevant data from the sensors.’ Quarq’s engineering director, James Meyer, is more blunt: ‘If you are building a sophisticated measuring instrument that is both lightweight and durable, then that flat-out costs money, no matter what you do.’ Garmin’s European product manager, Andy Silver, agrees: ‘The components are precision measurement instruments and the development process is highly involved and hence cost is significant.’ However all are in agreement that as the technology matures, costs may gradually come down, and cheaper alternatives will undoubtedly appear, but this is unlikely to happen overnight.

Meyer goes on to say, ‘As with most electronic devices technological advancements both improve the functional aspects of the product, hence they tend to get more sophisticated, while making them simpler for the consumer to use and understand.’ And within that statement lies the crux of a possible turning point for power meters and their appeal in the mainstream. Products that previously were only associated with sport scientists, top pros and coaches are evolving into something that no longer requires a science degree to understand and use.

That is clearly demonstrated by the most recent crop of power meters on the shelves. Products have focused on simpler fitting so you don’t need to be a qualified bike mechanic to install and maintain many of the devices, and it’s easier to understand the software too. Many now base the set-up and calibration on smartphone apps, something that most people use daily. The bottom line in Meyer’s eyes is straightforward: ‘If it’s too complicated no one would use it.’

CycleOps and its PowerTap hub was ahead of the game when it came to realising simple fitment was a key driver for sales – just swap out the rear wheel. This has clearly been a priority for the latest pedal-based systems from Garmin and Look/Polar, where the fitment element should not be beyond anyone’s capabilities. Even the most recent to join the party, Stages Cycling with its left-hand crank system, should not be beyond the realms of someone with only basic mechanical skills.

Internal affairs

While manufacturers have clearly established that simplifying fit and usage would help power meters to reach a wider audience, it’s important these attributes are not delivered at the expense of reliable and accurate data. In Silver’s opinion, ‘Cyclists want simplicity of installation and operation, and flexibility of usage, but they also need the data to be reliable, accurate and consistent. That’s the challenge and it’s not an easy balance to strike.’

At the heart of the internal circuitry of all the most credible power meters is the strain gauge. These tiny electrical components are responsible for gathering the necessary information to convert your pedalling input into the number you read on your display (it doesn’t appear by magic). The number of strain gauges in any given device varies, but don’t be fooled into thinking more is better. With complete unanimity all of the sources we contacted for this article were clear in their view that there are far more important considerations than the sheer number of strain gauges affecting the quality, and ultimately accuracy, of the data. Placement of the strain gauges is the priority – a classic case of it’s not what you’ve got, it’s what you do with it.

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Quarq’s Meyer says, ‘It’s feasible to build an incredibly accurate power meter with one single strain gauge. You only add further strain gauges when a mechanical shape requires it. Adding more per se doesn’t increase accuracy.’

One interesting problem facing manufacturers is highlighted by Bartholomew at CycleOps: ‘A significant challenge facing engineers is that in many cases the areas we most want to measure power [the drivetrain] are also areas where stiffness and efficiency is of top priority, and in order to get good power meter measurements you actually need to measure something bending or twisting.’ And Dr Auriel Forrester of SRM UK tells us, ‘The best place to measure power output is as close to the source as possible. Cranks make good sense logistically, because there is more space to work within them than, say, a pedal.’

This means that the options for future power meters are limited, but one possible exception is the shoe/cleat interface. Measuring directly under the sole of your foot is theoretically a great idea, although no system has reached production. 

Stages Cycling’s Pacocha suggests there might still be some interesting directions to explore: ‘It may be a while before we see another appreciable drop in component costs, so it’s likely instead we’ll be able to add features and interesting data streams, like g-force or lean angles, due to improvements in the hardware.’

So it could be that your little screen will soon be able to display even more data that you ever imagined, but remember one thing: power is nothing without understanding. All the data in the world will be useless to you if you don’t know what to do with it.

Watt the hell?

So what is a watt? Well, it’s more than just a number on the screen…

In lab coat tongue, Power is represented by the equation: 

(Force (N) x Distance (m) ) ÷ Time (s)
Force x Distance can also be termed
‘work done’ as it refers to the force
causing a displacement. 

1W = 1Nm/s and 1N = approx 102g 

So, on paper at least, it would take 1W of power to move a 102g mass a distance of 1 metre in a time of 1 second. But this is a very simplified model, as it assumes no other forces would act to resist movement. 

In non-boffin speak then, watts are simply a numeric value to represent the amount of torque (force on the pedals) you’re able to produce over a certain number of pedal rotations in a certain amount of time – in other words, how much work you are doing in a given time. That’s what makes watts such a valuable metric for performance monitoring. It’s a measure of actual energy output that is repeatable and comparable unlike, say, heart rate, which is merely reactive to the energy cost and also hugely susceptible to variation.

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