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’s 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 use 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
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 drivetrain losses. It also means your power output can be a bit lower if your drivechain 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.
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.
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.
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.
Our choice of power meters
You may notice that the majority of our favourite power meters are crank based. We’ve found many of these to be reliable – whilst others, pedals in particular, can be a bit vulnerable in poor weather. Hub based options have proven themselves hugely reliable, too, but they do limit you in wheel choice.
We’ve included some examples below – with each product is a ‘Buy Now’ or ‘Best Deal’ link. If you click on this then we may receive a small amount of money from the retailer when you purchase the item. This doesn’t affect the amount you pay.
PowerTap G3 Hub
Read more: PowerTap G3 hub review
Hub based power meters have been overlooked a bit in recent years, their lack of popularity largely comes down to the way they limit wheel swapping between training and competition. However, a crank based power meter limits you between bikes, and the G3 from PowerTap is a hugely reliable piece of kit.
Tester Ollie Bridgewood called it “highly recommended” and CW’s Michelle Arthurs-Brennan has used an older generation version for over six years without reliability issues. Battery changes can be a bit fiddly, but that means the unit is incredibly water tight – which results in next to zero problems. It’s a shame you don’t get left/right power but not a deal breaker.
The hub weighs 325g, so it does add a bit of weight in an uncomfortable place at the rear wheel, but it’s not a huge price to pay for detailed and trustable numbers.
Quarq DZero power meter
Read more: Quarq DZero power meter review
A winner in our 2018 Editor’s Choice awards, the Quarq proved to be accurate, durable and reliable, without being anywhere near one of the most expensive on the market.
Our tester escaped dropouts and power spikes during testing, and found the data reliable – reading about four watts above a Wahoo Kickr, which is a reasonable number accounted for via drivetrain losses.
Our tech editor Symon Lewis put this one up for its Editor’s Choice award, concluding” “The Quarq DZero power meter is a solid unit for those seeking easy, reliable and accurate numbers from a power meter.”
S-Works Power Cranks
The S-Works cranks from Specialized come fitted to some of their top end bikes, pre-installed, but the unit is available aftermarket too.
Specialized has used the technology created by 4iii – but it’s housed it within its own external crank, with a major focus on ensuring sufficient waterproofing.
The strain gauge itself is within two black pods, on the inside of the cranks – these weigh just 15g so there’s no real penalty.
Our tester Rupert Radley found the unit reliable, and didn’t suffer with dropouts or power spikes, stating “my whole experience with the product has been close to flawless” – the only downer was that it was a tad fiddly to fit.
Shimano Dura-Ace R9100-P power meter
Read more: Shimano Dura-Ace R9100-P power meter review
Shimano’s first crack at a power meter is a reliable and easy to use dual-sided meter that looks the business.
We’ve listed in our ‘best of’ guide, because it’s an option under high demand. Touches like the USB recharging port are great, and tester Richard Windsor found it was easy to calibrate and change batteries.
It wasn’t perfect though, being a first generation we’d expect some of its issues to be rectified through updates. For such a high price, it’s worth considering if other options might suit your needs and save you some cash too.
FSA Powerbox power meter
Read more: FSA Powerbox power meter review
With its comprehensive range of chainsets, a power meter is a natural extension of its product portfolio for FSA. It paired up with German power meter experts Power2Max to develop the Powerbox crank based power meter.
When we tested the Powerbox, we found that it was accurate and reliable and also coped well with the odd dousing with a hose pipe. It’s ANT+ and Bluetooth compatible, comes in carbon and alloy versions and with a wide range of chainring size options, including supercompact options.
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.
Used by British Cycling and the Australian Institute of Sport in the past, you know it’s going to be a decent piece of kit which provides a lot of information – such as m power and cadence, left/right balance, pedal smoothness, and torque effectiveness.
It’s also really easy to fit – just like a normal crank – and has excellent battery life. It uses ANT+ transmission, though the weight is a bit higher than others, at 691g.
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 layman’s 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.
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 imbalances before opting for a single sided meter. Note a 48/52% balance 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.
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 pedalling 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 2InPower.
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 3 £500.
Mid level – typically £700-1100
Mid-price starts to see pedal based systems and dual-sided meters. Crank and chainring systems also become available. Professional athletes are increasingly using meters at this price point. Examples include PowerTap P1 Pedals.
Top end – £1200 +
At the top of the market we find dual sided measurement and crank and spindle based systems. Examples include Rotor 2InPower £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.
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.
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.
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.