[This article was last updated on November 23, 2017]
Over the last few years measuring your power output has become a more and more popular part of cyclists’ training. Power meters have become cheaper as new manufacturers have entered the fray and there are more tools available to help you train with power. With meters now available for as little as £600, is it time to power up?
What is a power meter anyway?
When you ride a bike, you do work to overcome the forces of air resistance, gravity and tyre rolling resistance. Power is the rate at which you work, so the more power you can put out, the faster you’ll go. And after all, that's the objective of training.
The problem is, many things affect how fast you go, so it's hard to monitor your progress. Even if you test yourself on the same course every time, variables like the weather can make a difference.
This is less of a problem in other sports. Swimmers, for example, can use timed laps of the pool to measure their fitness, as the resistance of the water is more or less a given. Runners can similarly assess their training progress by measuring pace on a track.
Faster! (CC BY-SA 2.0 Dennis van Zuijlekom)
Measuring your power output gives you a way to directly measure your fitness. A power meter is a device that does just that.
A complete power meter system has two parts: the measurement device itself and a handlebar-mounted ‘head unit’ that reads your current power and stores ride data for later analysis. Power meter manufacturers make head units, or you can use a bike computer such as a Garmin GPS that has the capability to work with a power meter.
Why use a power meter?
Coach and training with power advocate Joe Friel calls a power meter “the most effective tool you can get to go faster on a bike”. Because a power meter measures how hard you’re working it enables you to train very precisely, and to measure your progress.
Before power meters became popular, cyclists relied on heart rate as a proxy for training effort. But heart rate can be affected by more than just how hard you’re working, and the objective of training isn’t just to develop your heart. Rather, you’re aiming to go faster, and that means, all else being equal, generating more power. It’s therefore more efficient to measure power.
It can also save you time. Friel points out that it can take time to get up to a target heart rate even though you’re working as hard as you need to in a training session. With a power meter you can tell instantly that you’re putting out your session’s target power and stay there. If you're strapped for time, a power meter lets you get the most out of your limited training hours.
Types of power meter
Power meters use tiny electronic devices called strain gauges to measure the force you’re exerting on part of the bike’s transmission. From those raw measurements, supporting electronics calculate your power, which is then transmitted to the head unit, usually by a low-energy small area wireless protocol such as Garmin’s ANT+ or Bluetooth.
Power meters have their strain gauges at different points in the path between your feet and the tyre that your effort travels along to propel you forward. The most common placements are in one or both pedals, one or both crank arms, in the chainring spider, or in the rear hub.
SRM crank (CC BY-NC-ND 2.0 by Kevin G Saunders:Flickr
The first widely-available power meter, from SRM, has its strain gauges in the crank spider, between the right hand crank and the chainrings. That means all the forces from both cranks go through the meter to be measured.
SRAM’s Quarq power meter and Pioneer’s system also have gauges in the crank spider, while PowerTap’s C1 chainrings move the measurement point one step along, but effectively do the same job.
An alternative that allows for a less-expensive power meter is to measure the forces in the left hand crank. In theory this might give incorrect data as it’s only measuring the power from one leg, but in our tests the Stages Cycling power meter, which uses this design, gave readings consistent with a PowerTap hub meter and Garmin Vector pedals. Pioneer also offers a left-hand-crank power meter.
A claimed advantage of power meters with the gauge in the crank arm is that they can be more accurate. The makers claim that the position of the gauge allows it to just measure the forces that propel you forward and not the twisting of the crank or other components. Verve Cycling takes this to its logical conclusion with its InfoCrank that has a measurement unit in each crank arm, and Rotor's dual-sided system works similarly.
In the US, 4iiii will install its Precision power meter in your existing left-hand crank arm.
The only bottom bracket power meter, from Ergomo, is available to fit square taper or Shimano Octalink cranks. It uses wires to carry data to its own proprietary head unit, but at €600 for a system, it’s an inexpensive entry to power measurement if you have a set of older cranks to hand, or can pick a set up on eBay.
Rotor's INpower also tucks the strain gauges and electronics into the crank axle, but you have to use Rotor cranks with it.
Look and Garmin are the two longest-established manufacturers of power-measuring pedals. This design allows for easy swapping of the meter between bikes. It’s not quite as trivial as just reaching for a pedal spanner, but it’s fairly straightforward.
Both Powertap and Favero also have pedal-based power meters. O-Synce has shown a system at trade shows but it has not yet become available.
Power-measuring pedals offer the ability to measure each leg’s power independently, and some are able to analyse your pedal stroke too.
On the same principal as left-crank meters, some pedal meter makers offer a single-pedal system that provides power data at lower cost.
PowerTap hub (CC BY 2.0 Glory Cycles)
Measuring power in the rear hub must be fairly tricky, as PowerTap remains the only manufacturer of a hub power meter, almost two decades years after introducing its first hub. Supported by relatively flexible frame ends, and hammered by road forces, the hub is a hostile place for delicate electronics, but PowerTap seems to have solved the problems. You can get a PowerTap hub either built into a wheel or a pair, or on its own so your favourite wheelbuilder can install your rim of choice.
A hub power meter is the easiest type to switch between bikes, though if you want power readings while racing then you have to train on your racing wheels. Power meter advocates would say that’s a sensible decision.
All your power meter options
What follows is an overview of all the currently available power meters, that's as comprehensive as we can make it. We kick off with the most recently announced models.
This is Italian electronics manufacturer Favero's second go at power-measuring pedals after the BePro pedals. While they don't seem to be available just yet, they look very very promising. The spec is like a wishlist of power pedal features: no external pods, so swapping between bikes is easy; Bluetooth and ANT+ communications protocols; left and right power; torque efficiency and pedal smoothness; Look Keo cleat compatibility; rechargeable; apps for iOS and Android; and a claimed weight of 299g/pair.
There's also a single-sided version, the Assioma Uno, for £455.
They're supposed to be widely available late November, and we have a set on test at the moment. If Favero has delivered on the promise, the Assioma Duos will be the lightest power meter pedals on the market, as well as the cheapest.
The VeloComp PowerPod works out your power by measuring the forces working against you, notably air resistance. It sounds like one of those ideas that's great in theory but can't possibly work in practice, but it's had favourable reports from riders who tried it and compared its data with other power meters. It also has the advantages of being very keenly priced, and easy to swith between bikes, as it sits on a GoPro-style mount under your bars.
FSA's Powerbox power meter crank borrows power2max technology and has an RRP of £599 for the aluminium version (including chainrings), though it can already be found for considerably less. That makes it the cheapest crank power meter we're aware of, and the cheapest meter that measures power from both sides, though FSA has not yet released the firmware upgrade that will allow you to see the left and right hand readings separately. It communicates using the ANT+ protocol and battery life is a claimed 300-400 hours from a CR2450 button cell. A firmware upgrade to allow Bluetooth communication has also been promised. Both it and left/right measurements will be paid-for upgrades.
Fancy a bit of DIY? The Watteam Powerbeat is a pair of sensors that you mount on your cranks yourself. That's right, you quite literally turn your existing hollow aluminium cranks into a pair of power-sensing crank arms by gluing sensors to them. That gives you two-sided power measurement at a bargain price, as long as you already have compatible cranks. Even if you don't, they'll work with Shimano 105 cranks which can be had for as little as £66.
And it works. The Watteam PowerBeat kit turns your cranks into an accurate, consistent double-sided power meter for a very sensible price, and the process of fitting them isn't nearly as scary as it sounds.
If you're happy with measuring power from just one side, there's a left-hand-crank version of the PowerBeat for £255.
Not yet available at the time of writing (November 2017) the Avio Powersense turns your cranks into a left-hand-only power meter. It communicates via ANT+ and Bluetooth and if Avio can actually deliver, it will be the cheapest power meter option by quite a large margin.
RaceFace and Easton's Cinch and is an axle-based power meter that works with the Easton EC90 SL road crankset or RaceFace’s mountain bike Next R crankset. Because the sensors are in the bottom bracket axle, it only measures left hand power, and then doubles it. It communicates with both ANT+ and Bluetooth protocols and has a claimed battery life of 400 hours between charges.
Arofly is a power, cadence and speed meter that attaches to the valve of your rear wheel and weighs only 10g, including its button battery. It sends your cycling data via a Bluetooth connection to be displayed in real time on a custom mobile app on your smartphone.
Dead cheap, dead simple, so what's the catch? It doesn't work very well. We found that it simply doesn't provide measurements that are consistent enough that it can be considered a useful training tool.
Luck Potentiometer — €200 per side
Spanish shoemaker Luck has cooked up a power meter that fits inside its shoes, putting the power sensor as close as possible to the source of your effort. The advantage is that it's trivial to switch between bikes, though you'll nee a pair of Luck's shoes too.
The 4iiii Precision is a crank-based power meter that delivers sound, usable data, as long as you're happy with the limitations of a single-sided system.
The Precision system consists of a tiny pod that's bonded to a non-driveside crank arm. In that way it's similar to a Stages unit. I used the Shimano Dura-Ace version (they're all Shimano) and it weighed just 9g more than the crank I took off, and that includes the battery. A Shimano 105 version is £349, and a Shimano Ultegra version is £429.
Shimano's power-measuring cranks aren't in the shops yet, but they'll have an RRP of £1,300 when they do. As well as providing for consumers, introducing a power meter crank will presumably allow Shimano to get its sponsored riders on an in-house device. It’ll be interesting to see how many of the World Tour teams will be using it next year.
It's crank based with strain gauges in both crank arms, so it can measure left and right legs separately. It has a discreet ‘brain’ that sits within the spider. See it up there (above) between the top two arms? I told you it was discreet!
It can be paired to third party displays, such as Garmin Edge bike computers. The system checking and firmware upload can be operated by your smart phone or tablet PC through a Bluetooth connection.
SRM — it stands for Schoberer Rad Meßtechnik, TLA fans — makes a wide range of power meter cranks, taking the original manufacturer’s right hand crank and installing its measurement unit in place of the crank spider. It’s a robust design with an excellent reputation for accuracy and reliability, backed by a three-year guarantee.
You can buy a PowerTap hub on its own or built into a pair of wheels for £849.50. The latest version seems to have ironed out the reliability niggles of previous PowerTaps, and is easier to get serviced if things do go wrong.
PowerTap says it has spent five years developing its pedals, a figure that’s believable considering how long others have taken to go from announcement to shipping product. Our first impressions are of a successful meter that’s consistent and easy to install and use.
There's also a single-pedal option, the £550 PowerTap P1S.
Find a PowerTap dealer
Read our review of the PowerTap P1 pedals
Read our review of the PowerTap P1S single-sided pedals
Verve Cycling’s InfoCrank comes backed by some big hitters — the company says it’s been commissioned by the Australian Institute of Sport to design versions for track, mountain biking and BMX. It’s claimed to be more accurate than other crank meters thanks to sensors in both crank arms; and to only need calibration after a crash.
With pedals and a rear hub too, PowerTap now has all the popular power-measuring points covered. It’s claimed to be the cheapest meter that measures power from both legs, which seems like a reasonable claim even if you have to buy a chainset to go with them. It comprises a sensor unit and a pair of 110mm chainrings, made for PowerTap by FSA. The whole shebang fits any 110mm five-arm crank; PowerTap is clearly going for the largest possible installed base for starters, but no doubt there will be four-bolt versions in the future.
The second incarnation of Garmin’s power meter pedals, the Vector 2 is available in two versions with meters in either the left pedal or both of them. The one-pedal version can be found for £474.99.
The improvements make the pedals easier to set up and switch between bikes. It's an expensive system but one that can give you a ton of information, and that will appeal to a lot of data-hungry riders out there.
The next generation of the Vector pedals — unsurprisingly dubbed Vector 3 — is due to land in shops next month. Garmin has done away with the pods, and the new version has both ANT+ and Bluetooth communications.
The Stages Power meter is lightweight, easy to fit and, according to our tests, it gives results that are comparable with those of systems costing twice as much. The meter is housed on a left (non-driveside) crank. You buy the crank with the power meter already installed and swap it for your existing left-hand crank. Stages offer various different models.
The range of power meter chainsets from SRAM and technology company Quarq stretches from basic models without chainrings up to the SRAM Red Quarq PowerMeter with an RRP of £1599.99 (but available for about £1300).
Pioneer makes both single- and dual-sided crank meters that have been received favourably. They’ve not been easily available in the UK, but that’s set to change as they recently picked up a distributor here.
An unusual feature of the Pioneer system is force and direction of force measurement. It measures 12 times per revolution and can display force in real time, so you can use it to analyse your pedal stroke.
Read more about the Pioneer power meter
Read more about Pioneer’s single-sided power meter
Find a Pioneer dealer
Rotor makes several models of power meter, both double- and single-sided as well as the stealthy Inpower meter whose electronics are tucked into the bottom bracket axle to protect them from damage. Rotor non-power cranks are among the lightest on the market, and the company has tried to keep the weight of its power meters down too.
Read more about the Rotor Inpower crank
Read more about the single-sided Power LT power meter
Find a Rotor dealer
Look was the first company to ship power meter pedals, in 2012, but sometimes being first to market just means you’re demonstrating to everyone else what not to do. While all other power meter makers were adopting ANT+ and Bluetooth, Look went with its own communication system that only worked with two head units from Polar. Nobody was very impressed with that.
The third-generation version is ANT+ and Bluetooth-compatible, opening up the full range of head units. There's also a single-sided version, dubbed Essential, for £670.55.
Aside from that the Keo Power has a good reputation for reliability and accuracy, but the price is still painful, especially now it’s no longer the only system that measures power from both legs.
Included for completeness as it’s not clear whether Ergomo is still available, this is the only power meter bottom bracket we’re aware of. It has a wired connection to its head unit, but the price for both is very reasonable.
Our official grumpy Northerner, John has been riding bikes for over 30 years since discovering as an uncoordinated teen that a sport could be fun if it didn't require you to catch a ball or get in the way of a hulking prop forward.
Road touring was followed by mountain biking and a career racing in the mud that was as brief as it was unsuccessful.
Somewhere along the line came the discovery that he could string a few words together, followed by the even more remarkable discovery that people were mug enough to pay for this rather than expecting him to do an honest day's work. He's pretty certain he's worked for even more bike publications than Mat Brett.
The inevitable 30-something MAMIL transition saw him shift to skinny tyres and these days he lives in Cambridge where the lack of hills is more than made up for by the headwinds.