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Power meters: 7 hidden hassles you'll want to try and avoid

Power meters are a definite Force For Good to the performance-minded cyclist... but they can sometimes do your head in too!

If you're a performance-orientated rider or you just want to get the highest level of fitness from a limited amount of time on the bike, a power meter is a great weapon to have in your armoury... but it has its downsides. Here are some of the irritating and sometimes downright frustrating experiences that we've suffered and heard about over the past few years.

Figures aren't comparable between devices

Power is an absolute measurement that is the same whether you have a headwind or a tailwind, whether you're going uphill or downhill, whether you're on a 10 grand superbike or a £200 supermarket special. That's why it's so valuable to cyclists. 

Garmin Vector 3 pedals.jpg

However, put two power meters on the same bike and they probably won't give you the same power figures. Some measure strain in the pedals (Garmin Vector 3 pedals, for example), some in the cranks (Stages), the spider of the chainset (power2max), the bottom bracket axle (Rotor INpower), the rear hub (CycleOps PowerTap G3)... They take their measurements and make their calculations in different ways. Some power meters are better than others at picking up sharp peaks and troughs in your power output too.

Find out how to choose a power meter

shimano_dura-ace_r9100-p_power_meter_figure_3.png

This (above) shows power measurements from a Shimano power meter (pink) and a PowerTap G3 hub (blue). The two lines are similar but not identical

Also, check out the marketing literature and you'll also see that manufacturers always give a margin for error. CycleOps claims that its PowerTap G3 Hub is able to deliver +/- 1.5% accuracy, for example, while Specialized claims the same for its Power Cranks (most claim somewhere from 1% to 2%, although they rarely specify whether that claim refers to a specific wattage and cadence). 

Say, for the sake of argument, you're putting out 300 watts. The PowerTap G3 Hub might give you a reading of 296 watts, the Specialized Power Cranks might say 304 watts. Each would be accurate to within its manufacturer's claims.

Even two units of the same power meter can give different power figures.

CycleOps_g3_rear_powertap1

All of this means that you can't really compare figures from different power meters in a meaningful way. Fortunately, that doesn't matter for most of us. We're most interested in how our power output alters over time, and a single power meter is good for gauging changes.

There's a new language to learn

Okay, so you've bought a power meter and you're getting some extra numbers on your bike computer. Great. Now what?

All the new figures and terms that you encounter can be intimidating, especially if you're not naturally number-orientated.

Shimano Dura-Ace R9150 Di2 - crank 1.jpg

Buying a power meter won't make you faster... Not in itself. It's using a power meter correctly that will help make you quicker or enable you to use your time on the bike more efficiently. That requires you to either learn how to use the data or to enlist the help of a coach or an online/app based system like Sufferfest​ or TrainerRoad that will give you power-based training plans and structured workouts to follow.

Thankfully, a lot of things stem from FTP, or functional threshold power – the average power you can produce for an hour. Get that sorted and you can build from there.

Go to our power meter reviews

We're not saying it's the most complicated thing in the world (unless you want it to be!) but you do need to be prepared to do some background work to get the most out of a power meter.

You'll make mistakes

At some stage you'll make mistakes with your power meter. 

Early on, for example, you might confuse your average power with your normalised power (which is used to allow for changes in ride conditions in order to give a more accurate depiction of the power expended) or compare an average power with the zeros left in (when you're coasting) with an average power with the zeros removed, leading you to wonder why your level of fitness has suddenly changed.Verve Cycling - 1.jpg

Even experienced power meter users make mistakes. You should 'zero offset' most power meters before every ride, for example (the Verve Infocrank never needs re-zeroing, according to the manufacturer). This simply means having the system measure the power at zero load and then having it use this value as the baseline for power measurement. It takes just seconds, but unless you have your bike computer prompt you to do it at the start of every ride, you're bound to forget occasionally and the accuracy of the data will suffer.

You'll get obsessed by numbers

A lot of cyclists are already preoccupied with numbers: distance, speed, cadence, elevation, gear ratios, heart rate, calories, weight, you name it! Introducing a power meter into your life gives you a whole lot more.

SRM CSM

Do you want to see your current power as it currently is, or as a 3-second, 10-second or 30-second average? Then you have to think about your FTP (functional threshold power), normalised power, power to weight, left leg/ right leg balance... the list goes on.

There's nowhere to hide from your power figures. You can't blame weather conditions or your riding buddies like you can for a low average speed.

Of course, all this information is great for honing your training and perfecting your race performance, but there's just that danger that you'll get obsessed!

There's temperature to consider!

A change in temperature can have an impact on the performance of a power meter because it causes the strain gauges to torque slightly. Thankfully, most power meters compensate for changes in temperature as you go. 

Stages R9100-L.01

For example, Stages says, "The strain gauges used in a power meter – regardless of whether it’s crank based, spider based, pedal or hub based – are made of metallic elements which are affected by even slight changes in temperature which, if not factored, can lead to inaccurate ride data. For this reason, Stages Power meters are equipped with active temperature compensation firmware, which automatically adjusts for temperature changes during your ride, so you can trust your data."

If your power meter doesn't have active temperature compensation, performing a zero offset (see You'll make mistakes, above) will achieve the same thing (accounting for any extra torque in the strain gauges). Obviously, stopping to zero offset your power meter isn't always an option, particularly if you're mid-race or riding in a group, which is why some power meters have an automatic zero function, meaning that they'll perform a zero offset during your ride. p2m_NGeco_FSA30.jpg

"It is possible to repeatedly set the zero point [of a power2max NG power meter, above] at the head unit, but it isn’t necessary!" says power2max. "This is performed by the system automatically when it is not under power. 'Not being under power' means a stop in l for at least two seconds during a ride. If a de-powering as described above is not possible, for example during a long mountain climb, then your power2max NG power meter automatically compensates for temperature."

All that said, you hear plenty of people complaining about various power meters giving inaccurate readings due to large temperature changes – Shimano's power meter chainset was initially criticised for having poor temperature compensation, for example – which suggests either a helluva lot of user error or that some manufacturers haven't yet got this completely right.

Dropouts in data... Grrr!

Some people complain about power meter data dropouts – you're riding along and the power figure is no longer there, or it's erratic, or it's just plain baffling. It's frustrating, to say the least. 

Some power meters are more prone to this than others. Frequent issues include a dodgy battery connection within the power meter, and the Bluetooth or ANT+ signal between the power meter and the head unit getting blocked. 

We obviously can't give you a solution to every issue here, but hopefully it's of some comfort to know that we feel your pain! If you're experiencing an issue, chances are that someone else has too, so your first port of call should be the manufacturer's FAQs and the 'support' section of their website.

You might be disappointed by what you find out!

If you're used to checking out the power files of pro riders from big races, you might well find yourself a little disappointed when you find out your own power-to-weight ratio. Even if you're king of your local chaingang, chances are that you're going to have your Tour de France dreams dashed. Sorry.  

Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now pushing 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.

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