Do You Really Need a Power Meter?

The little red box attached to Bjarne Riis’ handlebars as he raised his arms, resplendent in the Danish champions jersey, to celebrate his victory in the 1997 Amstel Gold Race was a source of great curiosity in the peloton. Inside that little box was a computer directly recording his power output as measured by his then state-of-the-art SRM power meter – data which I was astounded to discover can be downloaded and examined in excel here.

The first win with a power meter installed – Bjarne Riis, Amstel Gold Race 1997

Whilst SRM’s power meters had been around for at least 10 years prior to that day, their bulky design confined them to stationary bikes and training rides only. But that changed when Riis won that day, and as the technology developed over the next 10 years, increasing the accuracy of readings and reducing the weight penalty of the instrumentation, power meters became an unavoidable presence on almost every professional roadies bike. These days you would be hard pressed to find a single bike on the start line of the Tour without one.

So that must be it, right? If they’re all using them, I just need one? Well, in my opinion that depends on your answers to two key questions.

  1. How would you describe yourself as a cyclist?
  2. How much disposable cash do you have?

I’ll work through these one by one and try to give you a hand in deciding whether or not to pull the trigger.

How would you describe yourself as a cyclist?

Now I’m not a huge fan of pigeonholing cyclists into the increasingly irrelevant road or off-road, racing or touring buckets and I don’t recommend you do either. But when deciding whether you really need a power meter, it is definitely a good idea to start with a bit of honest introspection.

If after a few minutes of deep meditation you consider yourself to be a performance-driven cyclist – someone who wants to ride fast, race hard and train harder – then buying a power meter becomes a much easier question to answer. Whilst it is possible to train effectively on basic metrics like riding time, perceived exertion or the slightly more techy hear rate, none can give you a direct reading of your performance. You could be doing anything in the time you jot down at the end of a ride. You might perceive your ride to be hard because you had a few too many drinks the night before. Your heart rate might be high because of stress, or low because of fatigue. But with power, there are none of these ambiguities – there is just your power output in Watts, a direct measurement of the most important performance metric in cycling, especially when combined with weight (W/kg) for climbing or drag coefficient (W/CdA) for time trials and track. By using your power output to calculate your functional threshold power (FTP) and training zones, you can take your training up a notch with structure workouts that are simple to follow and easy to analyse.

An example of a power curve, a useful tool when training with power.

Ok, I need to be honest, there are still some imperfections with power meters – most tend to be accurate to within 1-2%, most will need to be re-calibrated from time to time, some only measure power on one side and double it and some will be measuring power output after efficiency losses in the drivetrain (eg. Hub based models). But the thing is, as long as your power meter is recording consistently, even if it is slightly off, it will still provide you with the benefits mentioned above.

Of course not everyone will see themselves as performance driven, so do those people still need a power meter? Well, no, they don’t need one, but they might still find that a power meter enriches their riding experience. Some folks just love data and there’s nothing wrong with that. It can be a great feeling to finish a ride and see that you’ve set your highest average power on a ride, even if you have no intention of showing that off at your local crit later in the week. But the difference for these people is likely to be question 2…

2. How much disposable cash do you have?

If this was a post advising you on sensible personal finance practices, then this would be number 1. But we’re all cyclists here so we know things don’t always work like that in our heads.

The fact is, despite prices falling in recent years thanks to a lot of competition and innovation in the market, power meters are still not cheap bits of kit.

The cheapest models at present are normally the single-sided crank based versions, from the likes of 4iiii and Stages, which you can find for as little as £250 in some places. These calculate your power output by measuring the flex of the non-drive side crank arm through a potentiometer and doubling this value to estimate the output on the drive side too. This means that accuracy is often a bit sketchier and you aren’t able to view your left and right balance, which might be a problem for a performance-driven cyclist – but is probably fine for the more casual user.

A Stages left crank arm power meter – one of the cheapest ways to get into training with power.
Favero Assioma Duo – my pick for the best value for money.

Pedal based models start at around £400 for a single sided model by Favero Assioma, up to £1000 for a dual sided Garmin Rally model. These types are particularly popular due to the ease with which they can be switched between bikes and the Favero Assioma’s are generally regarded as one of the best value options on the market, but are only available for road 3-bolt cleats (unless you want to do a DIY SPD conversion).

Then you have spider-based meters, from the likes of Quarq and SRM. These can be found from £350 – but you’ll need to provide your own crankset and chainrings for that price. A full crankset with power meter will be closer to £600. Historically these were the most accurate types, partly because they were the first type to be developed, but they aren’t easily transferable between bikes and a new frame with a different bottom bracket type could mean you need a new power meter too.

A standard Quarq power meter setup

If you’re going for performance, then those prices might seem like great value, particularly when stacked up against the prices of some less useful bits of kit (I’m looking at you Silca). But for others, it might seem like an extravagant spend. This bit really comes down to how you want to handle your money.

Conclusion

So, where do I sit on the matter? Well, I race very infrequently, maybe once or twice a year, and I certainly don’t have a structured training plan to follow in the run-up to those events. But I still have a power meter and a smart turbo trainer. There’s something about seeing what your body is capable of, in a unit that you can think of in terms of a number of slices of toast grilled, kettles boiled or lightbulbs lit, that puts your performance into some strangely enlightening context. Plus I’m always ready to start training for that tilt at the Tour as soon as Ineos give me the call.

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