What is a power meter? Do I need a power meter? Which power meter is best for me and what features should I look for and be aware of? All these questions and more are answered in our comprehensive guide to power meters, including links to reviews of the latest products

What is a power meter?

A power meter is a device fitted to a bike that measures the power output of the rider.

Most commonly, power meters use strain gauges that deflect slightly when a force is applied. By measuring this torque and combining it with angular velocity, power (measured in watts) can be calculated.

If you want to get the most out of your training then a power meter is the best tool to quantify your workouts.

As ever, there no single power meter that is the best. This will depend on how you intend to use it, your bike, your bike placement options, your budget and if you want to used it with more than one bike.

What are the different types of power meter?

Currently, power meters can be placed in five key areas of a bike. Of course, each has their own advantages and disadvantages. These are:

  • The rear wheel hub
  • The bottom bracket/spindle
  • Chainrings and crank spiders
  • Crank arm
  • Pedals

Hub based systems such as the PowerTap G3 are amongst the most simple power meters on the market. With fewer forces acting on the strain gauges, many engineers regard the hub as the most accurate location to measure power.

Power measurement will be slightly lower here than on a pedal or crank system as you’re measuring what is left, post drive train losses. It also means your power output can be a bit lower if your drive chain is very dirty.

Bottom bracket systems can be accurate and low maintenance. However, installation is more difficult and is made all the more complicated by the varying bottom bracket standards available today.

Bottom bracket systems can be accurate and low maintenance

Factor in that a system of this type may not fit your bike and it is also likely to mean you have to run a different brand chainset to the rest of your groupset. Examples include Rotor INPower.

Chainring based power meters can be very accurate but it is worth factoring that they don’t actually measure individual left/right power. They can estimate it, though.

>>> Should power meters be banned from pro racing?

Similar to bottom bracket systems, they are not as easy to swap between bikes, as say pedals, and there can be compatibility issues. Examples include the fabled SRM (the most popular choice amongst pro riders), Power2Max and Quark.

Crank arm based systems can be relatively easy to swap between bikes, too. Like pedals, they have the potential to be single or double sided and popular examples include the Stages crank arm and 4iiii precision meter.

Power meter pedals. It’s important to tighten them to the correct torque to get an accurate power reading

Pedal based systems are easy to fit and swap between bikes, but can be less accurate owing to the complexity of the force measurement and being exposed, makes them at greater risk of damage.

Popular examples include Garmin Vector and Power Tap P1 pedals. Power meters of this type can also be single or double sided.

Our choice of power meters

Verve Infocrank power meter

Read more: Verve Infocrank power meter review

The verve Infocrank has got a lot going for it. It’s really precise, which makes it a great training tool.

It’s also really easy to fit and has excellent battery life

Buy now: Verve Infocrank from Tredz for £1260

Powertap P1 pedals

Read more: Powertap P1 pedals review

We reckon that this is the most versatile and easy to install power meter on the market.

It works well, too. It records data accurately – just be sure to stay on top of its firmware updates.

Buy now: Powertap P1 pedals for £947.98 from Wiggle

Stages power meter G2 Shimano Dura-Ace

Read more: Stages power meter G2 Shimano Dura-Ace review

This is a great little package from Stages, offering almost all the crank offerings from Shimano, SRAM and Campagnolo.

Plus, it’s compact, lightweight and positively wallet friendly compared to some options.

Buy now: Stages power meter G2 Shimano Dura-Ace from Evans Cycles for £649

Quarq Riken 10R power meter

Read more: Quarq Riken 10R power meter review

The Quarq Riken 10R power meter is easy to pair and calibrate and available in a range of sizes.

More importantly, it’s also really accurate.

Buy now: Quarq Rike 10R power meter from Tredz for £799

Rotor INpower power meter

Read more: Rotor INpower power meter review

300 hour battery life isn’t something to be sniffed at, plus it’s accurate for a single-sided system.

Buy now: Rotor INpower power meter from Chain Reaction Cycles for £700 

Key Features of Power meters explained

Firstly, what is power?

We spoke to Professor Louis Passfield (pictured), currently based at the University of Kent Centre for Sports Studies.

The maths: power (W) = force x distance / time

Watts are the energy required to a move a mass a certain distance in a known time period. 1W = 1Nm/s in other words to move one Newton one metre in one second costs one watt of energy.

So in bike speak, the mass is you plus your bike, and the distance is the ground covered.

Moving a bike, though, is a far more complicated scenario, as its resistance to motion is far from consistent.

In laymans terms, then, this equates as: power = force x velocity

And that is the key to understanding how a power meter works. It’s essentially applying that equation to a given part of the bike – be that BB axle, crank, hub, pedal axle etc.

Accurate measurement of this force is one of the biggest challenges power meter manufacturers face. So the smallest details become important.

For instance, the placement of the gauges, the quality of the gauges themselves and even the temperature of the measured material.

Single sided power meters

These units measure power from one side, usually the left, and then double the reading to estimate your total power output from both legs.

4iiii precision 2.0 power meter 2

A single sided only measurement means doubling a single legs power may not be a fully accurate representation of your power, but it can mean they are more affordable.

It may be worth checking if you have significant inbalances before opting for a single sided meter. Note a 48/52% ballance between legs is common.

Combined power meters

These units effectively combine the power from both right and left legs and do not measure it independently. An example would be a PowerTap G3 hub or SRM.

>>> Are power meters killing the art of cycling coaching

Note that these systems, although accurate, will not differentiate which leg the power comes from.

Left/Right side independent measurement

This is found on more modern and more expensive power meters that have gauges in multiple locations, such as pedals and some crank based units.

This can be useful in establishing if you have an imbalance (one leg much more powerful than another) and for working on pedaling technique.

This can be especially useful if you are recovering from a single leg injury.

This is limited to power meters that measure power in more than one location, such as pedals, but also more expensive crank based units, such as Rotor 2In Power.

Connectivity

The vast majority of power meters transmit via ANT+ (including all in this test) allowing them to connect to most bike computer system, including Garmin.

Newer power meters are also offering Bluetooth Smart connectivity, which is useful for connecting to smart phones or updating firmware.

How much do power meters cost?

Entry level – Typically £400-£700

At this price you are likely to get a single sided measurement, that doubles the reading to estimate both legs. PowerTap hubs are also available at this price. Stages 105 crank £449, Powertap Hub £500 and Vector S £499.

Mid Level – Typically £700-1100

zwatt power meter

Mid price starts to see pedal based systems and dual sided meters. Crank and chain ring systems also become available. Professional athletes are increasingly using meters at this price point. Examples include Power Tap P1 Pedals £999.

Top End – £1200 +

At the top of the market we find dual sided measurement and crank and spindle based systems. Examples include Rotor 2In Power £1200.

How to use a power meter

If you want to learn about how to ride with a power meter, click on the link here. It has lots of useful information about how get the most out of your gadget and how to apply the numbers to your training. Essential for those coffee stop power meter chats.

 

Quarq have a new power meter, a Shimano specific model called the Elsa RS

 


Why is it useful?

Monitoring your speed can tell you only so much about a ride, heart-rate monitors can tell you a bit more, but knowing your power output is a quantitative, repeatable way to assess how hard you are actually working.

Power data can accurately determine the specific performance requirements of a given event/discipline. Basically, they allow you to be more objective with your training.

For example, you might have got a slower time over a given training route, but if your power numbers are up, and your heart rate is reduced then it’s pretty conclusive – your training is working!

Power can also tell you when it’s time to rest. A higher heart rate than normal at a certain power level means it’s probably time to cut a ride short and head for home.

Should I buy a power meter?

 

Really, it depends what you want to get out of your training. Here’s the pros and cons:

Benefits of a power meter:

  • Eliminates guesswork from gauging exercise intensity, so training becomes less haphazard.
  •  Quantitative tracking of fitness levels over time (when combined with other physiological data – heart rate etc) that provides conclusive evidence of training adaptations, including overtraining.
  •  Help to define your weaknesses.
  •  Monitor your effort levels (pacing) during an event.
  •  Train more specifically for the demands of your chosen event(s).
  •  Aerodynamic position testing.

Shimano Dura Ace 9000 SRM Chainset

Limitations of a power meter:

  • Best suited to a rider who is interested in analysis and number crunching
  •  It takes patience, learning and dedicated training to reap the rewards.
  • Interpretation of data requires knowledge and experience, either yourself, or with the help of a coach.
  • You can easily get bogged down by numbers. Don’t forget the fundamentals of why you ride a bike – to enjoy it.

Five things we recommend before you start

1) We can’t stress this enough… Have a clear idea about how you intend to use a power meter in order to get the most out of owning one. Bragging rights in the cafe or just getting one because your mates have all got them is likely to be a big waste of your money.

2) Get a fitness test so you can be conclusive about what your starting point is and also provide clear goals/targets to re-evaluate.

3) Understand training zones and the need for rides to be more specific and outcome-dependant. Be aware this may mean some rethinking of your daily rides or habitual old routes.

4) Consider a coach and following a set training plan to ensure your power meter is going to provide the best return for your investment with an upward spiralling of your wattage figures.

5) Be clear about the bike, or indeed the possibility of multiple bikes that you would like to use the power meter on. This will help steer your purchasing decision, and potentially cut down your options.

Rent-a-meter

Trouble deciding to make the leap? Why not rent a power meter?

There’s a whole host of companies across the UK who offer the latest and greatest power meters from testing.

  • Tim Phillips

    I love the way these things on forums always get out of hand and lead to name-calling. Grow up boys! (oh, I’m a PhD physicist too)

  • Anthony Bowles

    Tommy Voekeler won the Tour de Yorkshire using his loaf, not maths!

  • Sebastien Cosnefroy

    This article is so badly written.. “…costs one watt of energy.”: watt is a unit of power not energy!

  • Gav Z

    I’m no keyboard warrior, I’d say it to your face any time, but OK you were just joking. Fair enough. But there IS an anti-geek vibe in your country and mine. The US and UK are falling way behind the far east in hi tech. manufacturing. I worked at a national lab in the US for two years. We have talent, but there are fewer science graduates year on year, certainly in the UK.

  • Harri

    Are you really sure that the “country is going down the tubes” because of a guy making a joke or for the wolly that gets upset by a keyboard warrior (you do know in replying first time that makes you no better then me fam 😉 ) and to help you out you do know the usa produce the greatest scientists and as for engineers? probs the usa as well blud i also know the uk produce a very high level of engineers and scientists as well
    so go back to getting upset about me and my joke
    oh yeah i added no grammar to my reply just to make you more upset about this country going to the dogs
    happy Friday Gav z

  • Gav Z

    Married for 10 years with 2 kids. But yeah, I know yours is the attitude of non scientifically minded people towards the technically minded. Which is exactly why this country is going down the tubes. The Chinese are turning out vast numbers of scientists and engineers, to sell us phones (like the one in your pocket), computers and the tech. of the future. Rejoice in that, why don’t you.

  • Harri

    you guys need to get girl friends!

  • Gav Z

    I agree. It is a fairly decent article.

  • Dan

    Well, I’m not a theoretical physicist. I’m an experimentalist (and we’re talking about a measurement device), and just saying “energy expended per unit time” does nothing to explain to the general audience how these power meters actually work, which was the point of the article. I stand by my conclusion: This article was actually done pretty well, especially for a sports journalist.

  • Gav Z

    Dan, I’m a Ph.D. physicist too (really). I have a Ph.D. in theoretical nuclear physics (with computational physics). At its simplest power is related to energy, and,granted, that does not have to involve mass per se. But the SI unit of power is defined using mass (as you know), and of course we have mass energy equivalence, E = mc^2. 🙂

  • Dan

    Ok, I’m a Ph.D. physicist, really. Both sides are a bit right here. It’s true that the moving mass is not directly involved in determining power for steady motion especially. The resistances to that motion are, things like wind… which doesn’t depend on the mass at at all.

    However if we look at power from the perspective of the bike on the whole instead of the pedals (yes you can do that) then power is the applied force at the ground times the velocity (there are some definition technicalities to work around here, but it’s all ok). But velocity means by definition the center of mass motion so it’s not such a terrible linguistic mistake to talk about the force acting to move a mass. Yes some forms of power don’t even involve mass at least if viewed narrowly enough, like radiative power. However that doesn’t involve force either. Radiative power is calculated only from the fields.

    The statement did not clearly say that power depends on the amount of mass, and having dealt with quite a bit of scientific reporting, I can say that this is actually quite good and certainly much better than average. It’s amazing how many sellers of energy related products even get these things wrong, especially regarding electricity, batteries etc.

    There is a very interesting point in here for cyclists though. Weight of your bike doesn’t matter nearly as much as you think. All that energy in the moving weight helps keep it coasting longer. The energy isn’t gone and it doesn’t suck up more power during steady motion.

  • Paul Appleyard

    Yes, likely true. The simple aero drag formula has air (or ‘fluid’) density as a coefficient.

  • Barney Laurance

    Agreed. And mass matters in surprising ways. In air resistance it’s the mass of the air which matters, not the mass of the bike or the rider. I believe that’s why hour record attempts are made in uncomfortably warm veloodromes – warm air is lighter.

  • Paul Appleyard

    OK, the people writing the article don’t know physics for toffee, but mass is at the heart of the definition of the Newton (the unit). And in mechanics power is force times velocity. But OK power in its purest sense doesn’t have to involve mass at all, eg. the power in electric currents or EM waves.

    They should have just said the “energy expended per unit time”.

  • Barney Laurance

    (In steady riding on flat road power is used to overcome a combination of rolling resistance and air resistance, proportionally more of the latter at higher speeds. Neither are mentioned in the article.)

  • Barney Laurance

    I’m aware of the definition of the Newton. As you said, it’s the force needed to *accelerate* 1kg at 1m/s/s. The mass matters if you’re accelerating or climbing, but not much for cruising on the flat.

    The article implies that a Newton is a measure of mass, which is wrong.

  • Paul Appleyard

    Wrong. Mass is very much at the heart of the definition of power. The definition of the Newton (unit of Force) is force needed to accelerate 1 kilogram of mass at the rate of 1 metre per second squared. The definition of the watt is joules per second, but that is derived from Power = Force * Velocity. The SI unit equivalence for the watt is 1 kg·m^2/s^3 – you’ll note the kg in there. So really mass has everything to do with it!

    Some A level physics needed methinks.

  • Guest

    Wrong. Mass is very much at the heart of power. Definition of the Newton is

  • Barney Laurance

    I think your sentance – “Watts are the energy required to a move a mass a certain distance in a known time period.” is misleading. Watts are not energy, and its about force, not mass. Mass has very little to do with it, except when you are accelerating or climbing. Newtons measure force, not mass.

    Power is force times speed, so its how hard you are pressing the pedals multiplied by how fast the pedals move in the direction you press. If you press the pedals with a force of one newton (roughly equivalent to the weight of an apple) while moving it at one meter per second, then that’s one watt of power. Double either the speed or the force and you double the power.

    Multiply that by the time you continue and you get energy. One watt for one second is one joule.

  • Lee

    You made it sound more complicated than it really is. Power is simply a measure of how hard and fast you are pressing the pedals.