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, was available to fit square taper or Shimano Octalink cranks. It used wires to carry data to its own proprietary head unit, but at for a system, it was an inexpensive entry to power measurement if you had a set of older cranks to hand.
Rotor's INpower also tucks the strain gauges and electronics into the crank axle, but you have to use Rotor cranks with it and similarly the Easton/RaceFace Cinch power meter measures power from the axle.
Look and Garmin are the two longest-established manufacturers of power-measuring pedals. This design allows for easy swapping of the meter between bikes. Refinements to these pedals in the last couple of years mean that with the latest models it's as trivial as just reaching for a pedal spanner.
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, most 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.
PowerTap's P2 pedals are an evolution of the P1 pedals from 2015 rather than a radical redesign. They are a claimed 34g lighter, now coming in at 400g a pair, and the battery life has been extended from 60 to 80 hours, using the same AAA battery. And that’s it, that’s all they’ve changed. Aside from the change from black to silver, there are no other significant changes.
There is the same ANT+ and Bluetooth Smart compatibility, dual-sided power reading, Look KEO cleat interface, 2-year global warranty and 14mm stack height.
It's a good bet that they'll be functionally almost identical to the P1 pedals, which were very easy to set up and use.
When Specialized launched the latest version of the Tarmac Disc, they also entered the power meter market with a range of four power meters, two double-sided models based on Specialized's own S-Works cranks and on the Shimano Dura-Ace cranks, a single-sided S-Works crank and a single-sided Shimano Ultegra crank.
Specialized uses Canadian company 4iiii’s technology but did a whole bunch of its own development and testing with the Locomotion Lab in Boulder, Colorado to ensure the accuracy meets its bold claims.
The accuracy of each power meter it has developed is a claimed +/-1.5% with temperature compensation firmware, and ANT+ and Bluetooth are both supported for easy compatibility with many third-party devices. Specialized has also developed an app for setup and diagnostics.
The lightest setup, without chainrings, is the S-Works carbon dual-sided power crankset, which weighs a claimed 440g for a 172.5mm crank length.
Look's latest power meter pedals are a collaboration with original power meter company SRM, which should be a winning combination of Look's vast pedal expertise and SRM's ability to create reliable power-measuring electronics. The external pods of previous Look power pedals are gone; everything is contained in the pedal's carbon fibre body including rechargeable batteries that Look says give 100 hours of riding time.
As well as the double-sided pedals linked above, there's the inevitable £739 single-sided pedal that measures one side and doubles it, and a £1,949 bundle of the double-sided pedals with an SRM PC8 computer.
Announced in April 2018, the IQ² (say: IQ Square) power meter was supposed to sit between your cranks and pedals so there'd be no need to replace anything. It rapidly smashed its Indiegogo crowdfunding target; at the time of writing orders total well over £1.5 million.
The IQ² folks claimed some very clever manufacturing techniques help keep the price down and of course you wouldn't be buying a crank or pair of pedals to get a power meter. Potential problems included the 32mm increase in the space between your pedals and the patchy history of crowdfunded power meter projects, many of which have started with claims of wonderful products and then collapsed in ignominy and unhappy customers.
It was due to ship in November 2018, later put back to February 2019, and then on May 3 the company announced that they were going to make complete pedals instead because they'd been unable to stop constant changes in the behaviour of the thread from influencing the readings. Downside: further delays. Upside: an SPD-style double-sided mountain bike pedal is promised along with a Keo-compatible road pedal.
The Zpider is a double-sided crank power meter based on an FSA Gossamer crankset. It comes without chainrings, but it's compatible with Shimano four-bolt, 110mm BCD rings, so Team Zwatt is clearly assuming we all have a pair of those already, a reasonable assumption.
The Zpider has a built-in rechargeable battery with a claimed 240-hour life and magnetic charger. It communicates by ANT+ and Bluetooth.
If weight's important to you, there's a carbon fibre version based on an FSA K-Force Light crankset for .
Giant Power Pro cranks — NA
At the moment you'll have to buy a Giant Defy Advanced Pro 0 or Liv Langma Advanced Pro 0 to get a set of Giant's Power Pro cranks, but Giant says they'll eventually be available as a standalone item.
Built, as you can see, into a Shimano Ultegra crankset, the Power Pro communicates with your bike computer via ANT+ and can calculate pedalling angles and force and help you evaluate your pedalling efficiency.
Power2Max makes power-measuring spiders to fit other manufacturers' crank arms, with varying degrees of functionality depending on how much you spend.
You can get the spider on its own if you have Rotor, SRAM, Cannondale or Specialized cranks, or get it the NG models installed in FSA, Rotor or Campagnolo cranks.
The three models for road bikes are:
NG Road with claimed +/-1% accuracy, ANT+ and Bluetooth connectivity, and the ability to measure left/right balance, pedal smoothness and torque.
NGeco Road with claimed +/-2% accuracy, ANT+ and Bluetooth connectivity, and an optional firmware upgrade to measure left/right balance and pedal smoothness.
Type S Road with claimed +/-2% accuracy, ANT+ connectivity, and left/right balance.
All three measure cadence too.
And the award for the most imaginatively-named new power meter goes to…
Joking apart, third time's the charm for these pedals. Garmin has completely redesigned its Vector pedals, and the Vector 3 system is excellent. You get accurate power readings, they're even easier to swap between bikes, they look much neater and they're even a bit lighter. Add to that the fact that the RRP has dropped to £849.99 and they're an enticing proposition.
The Vector 2 system's weak point was the transmitter pod. It was an extra thing to remove and swap, and the connection was a bit fiddly, but most of all they were a bit prone to failure: I've had to buy at least two new ones, at £60 a pop.
The Vector 3 is an entirely new design, and it does away with the pod completely. All the electronics are contained within the new pedal body. Everything has been redesigned: the electronics are new, of course, but so is the pedal body, and the axle, and the bearings. There's really nothing left of the Vector 2.
These pedals transmit on ANT+, so you'll be able to pair them up with your Garmin/Wahoo/[insert your GPS manufacturer here] head unit and get all your data. New for the Vector 3 is Bluetooth Smart connectivity. You don't get all the metrics that you get with ANT+, because the Bluetooth protocols don't support some of it. But it's easy to get power and cadence on Bluetooth devices, and that could be really useful.
Benchmarked against a PowerTap hub and a Kickr smart trainer, the Vector 3s are consistent and accurate, and provide a serious nerdfest of data.
The Vector has really come of age with this redesign. It's always been a good quality system with repeatable and accurate power measurement, but pretty much everything about the new pedals is an improvement. They're probably the best power-measuring pedals you can get.
This is Italian electronics manufacturer Favero's second go at power-measuring pedals after the BePro pedals. 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 £400.
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 switch 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 one of the cheapest crank power meters we're aware of, and the cheapest meter that measures power from both sides. It communicates using the ANT+ protocol and battery life is a claimed 300-400 hours from a CR2450 button cell. A recent free firmware upgrade allows you to see the left and right hand readings separately, and enables Bluetooth communication.
If the PowerBox Aluminium's not-unreasonable 750g weight is too much for your best bike, there's a 585g version with carbon fibre arms for about £1,130.
Now shipping, the Avio Powersense service turns your cranks into a left-hand-only power meter that communicates via ANT+. You send in your crank, and Avio sends it back with the power-measuring unit attached, or you can buy a complete chainset with the device fitted. We're hoping to get a set in for test soon, but it has to be said you can't argue with the price.
Avio now offers a £225 DIY kit that includes all the gubbins necessary to turn a Shimano left hand crank into a power meter. Alternatively, you can buy the device fitted to a 105 or Ultegra left hand crank, or as part of a complete crankset.
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.
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, or you can get a complete Praxis Works Zayante M30 crankset with the 4iiii meter attached for £420.
Shimano's power meter is 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 from £624. 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.
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.
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 for Shimano, FSA and Cannondale cranks.
Stages has also recently introduced double-sided models built into Ultegra and Dura-Ace cranks.
The range of power meter chainsets from SRAM and technology company Quarq stretches from basic models with aluminium arms up to the SRAM Red AXS Quarq PowerMeter for £1,070.
Pioneer — NA
Pioneer makes both single- and dual-sided crank meters that have been received favourably, but they don't seem to have a distributor in the UK at the moment.
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.
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.
Look Keo Power Dual Mode pedals
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 was ANT+ and Bluetooth-compatible, opening up the full range of head units. With the advent of the Look/SRM Exact, they seem to have just about vanished from retailers.
Included for historical interest as Ergomo Systems' website has vanished, this was the only retrofittable power meter bottom bracket we’re aware of. It had a wired connection to its head unit, and the price for both was very reasonable, but it's clearly been superseded by wireless power meters built into modern cranks, pedals, hubs and so on.
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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.
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