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Power meter buyer's guide

By Bruce Lin

You are an engine, and without you, your bike is powerless. Like the engine in a car or motorcycle, the amount of power you produce can be measured. The tool that quantifies your work is the power meter.

A power meter allows riders who are serious about performance and training to monitor their workload, track progress, and pace efforts during important events or races.

Quarq power meter road gravel bike Chris MillimanRiding a bike equipped with a Quarq power meter | Photographer: Chris Milliman

If you’re curious about diving into the world of cycling with power, this guide will explain the ins and outs of how power meters work, the pros and cons of different power meter options, and how to use your power meter to extract the most benefit.

Contents

Why use a power meter

Power meters measure how much work a cyclist is doing on the bike and express it in watts. The ability to measure an athlete’s power is something unique to cycling. Other endurance sports like running and swimming are limited to using heart rate, RPE (rating of perceived exertion), and time to measure work. You may already be familiar with heart rate monitoring. Perceived exertion on a scale of 1-10 is easy for anyone to understand, and anyone who's run a mile can grasp the concept of pacing for a mile or another fixed distance. But those are imperfect tools.

“Heart rate can be affected by a lot of factors — caffeine, sleep, and stress,” says Nate Keck, product manager at Quarq. “It’s also an indirect measurement of what is actually happening. Heart rate has lag while power is instantaneous. If you go into a sprint at a power of 1,000 watts, you see that number instantly. But your heart rate may take 30 seconds, a minute, or even more to respond.

“RPE can measure effort, but when talking about someone’s perceived effort on a scale of 1-10, my 10 is probably different than your 10. People have different pain thresholds. With perception, there’s always some inherent error.”

Quarq power meter road gravel bike Jordan Clark HaggardA spider-based Quarq power meter | Photographer: Jordan Clark Haggard

Heart rate and RPE can be useful for cyclists, but power is the ultimate training tool. It provides the most accurate and complete picture of how much work the rider is doing during a ride, race, or workout. Environmental factors like wind and hills, and ride metrics like speed that may skew your perception, but won’t skew your power numbers. The only thing that matters is the actual effort.

The vast majority of training plans and advice you will find online will use power as the foundation for structured workouts. Measuring your power gives you accurate and consistent targets to hit during a ride so you can train effectively. This allows you to improve specific aspects of your fitness and reliably get results.

It’s always possible to train without a power meter. Many riders still do. But anyone seeking serious improvement in their performance will benefit from using a power meter for structured training and data-driven riding.

How a power meter works

Power equals force times distance over time:

Power = Force x Distance / Time

For a power meter to work on a bike, it has to measure the amount of force a rider is generating, and how fast that force moves (speed = distance / time). When pedaling a bike, the force comes from the torque produced by a rider’s legs pushing down on the pedals. Speed comes in the form of RPM (revolutions per minute).

To measure force, power meters have strain gauges that use an electrical impulse to measure deflection inside the power meter. Deflection changes the resistance in the gauge and this resistance can then be translated into torque. Then accelerometers in the power meter derive RPM. RPM is usually measured at the cranks (a.k.a. cadence) but it can also be measured at the wheel. Multiply torque by RPM and you have power. A power meter then sends that power number to be displayed on your head unit or other display.

Types of power meters

There are myriad power meter options on the market. The main differentiator most riders will notice is cost, ease of installation, and where the power meter is located on the bike. In practical terms, there are really only five locations on the bike to measure power:

The sections below list popular brands and models, an approximate price range for entry-level to high-end options in each category, and their various advantages and disadvantages.

Crank Spider

Popular Options: Quarq, SRM
Approximate Price Range: $600-2,000
Advantages: Accurate, reliable, central measuring location on bike, protected from elements
Disadvantages: Cost, some limited crank options

Quarq Power MeterQuarq DZero power meter installed on a SRAM Red crankset

Power meters located in the spider of a crankset have historically been the gold standard for power meters. SRM was one of the first power meters commercially available. American racer, Greg Lemond, famously began testing one all the way back in the late 80s. Currently, Quarq and SRM are the two leaders in this segment. They enjoy fairly widespread use among professional racers.

“Spider-based units are more accurate because they measure both left and right leg power,” Keck explains. “The spider is like the heart of your bicycle so it's a great place to measure. Also, it’s hidden from the elements more, meaning it’s less likely to get damaged and it stays a bit more sheltered and safe.”

Spider-based power meters are generally purchased as part of a complete crankset or as a standalone spider to fit your current crankset. This can be a limitation if you prefer a specific crankset or bottom bracket standard that isn’t available, or if you wish to easily move your power meter between bikes. You will have to remove your crank to install the power meter which requires a small amount of mechanical knowledge. In some cases, you may need to purchase new chainrings that are compatible with the spider (e.g., if your crankset is equipped with direct mount chainrings).

In general, spider-based power meters are reliable, provide consistent and stable power numbers, and are well-regarded. Many serious cyclists and racers who need accurate and consistent power data, are willing to spend the extra money on spider-based units.

Quarq power meters are popular, easy to service, easy to change batteries on, and very accurate. SRM units are known to be impervious to the elements, but they require factory service to change the battery (which lasts 2-5 years). Newer SRM Origin models, however, are rechargeable and many SRMs can be upgraded to rechargeable.

Crank Arm

Popular Options: Stages, 4iiii Innovations, Pioneer
Approximate Price Range: $300-1200
Advantages: Cost, simplicity, large variety of compatible options
Disadvantages: Single-side measuring, slightly more exposed to elements, potential error for left-foot-forward riders, potential frame clearance issues

Stages ultegra crank arm power meterStages Ultegra power meter crank arm

Crank arm-based power meters gained instant credibility when Team Sky, one of the most dominant cycling teams of the last decade, moved to Stages power meters in 2014. One of the major claims for making this move was improved consistency because crank arm power meters only measure on one side and eliminate the variance between the legs. Most crank arm units measure power from the non-drive crank arm and then double it to give power numbers that are inline with spider- or pedal-based systems.

Crank arm-based units are more cost-efficient than spider-based units and are easier to install. They require you to remove the non-drive crank arm and replace it with a compatible power meter crank arm. Manufacturers produce a wide range of units that are compatible with all bottom brackets, giving riders a lot of options.

Stages, Pioneer, and 4iiii also provide a “factory install” option. Riders can send compatible cranksets to the manufacturer and have a power meter installed on their current crank arms. This saves money and reduces waste.

Though single-sided power measurement is consistent and effective, some argue that it provides an incomplete picture.

“It only gives you a portion of the story,” says Keck. “Rarely do cyclists pedal and produce power at a perfect 50/50 split. It’s very common that one leg is anywhere from 2-9% off compared to the other leg. Your numbers and data could be significantly off.”

There are dual-sided crank arm power meters available from Stages, Pioneer, and 4iiii, but they are currently limited to specific crank models (Shimano Dura-Ace and Ultegra are the most common). Dual-sided units, however, are typically no less expensive than their spider-based counterparts.

Stages Ultegra crank arm power meterCrank arm power meters have a few potential issues. The housing for the electronics and battery protrudes from the inside of the crank arm. This can cause clearance issues with certain frames (manufacturers provide specs for how much clearance is necessary for their products). Some off-road riders who ride with their left foot forward have seen erroneous power spikes when coasting with pedals level through rough terrain. Crank arms are also slightly more susceptible to damage than crank spiders, especially from heel rub, crashes, or trail debris.

All this being said, crank arm-based power meters are incredibly popular because of their cost, ease of use, wide range of options and compatibility. The technology is constantly improving and crank arm-based units are a great option for everyone from beginners to expert power users.

Pedal

Popular Options: Garmin Vector, PowerTap P1/P2, SRM EXAKT
Price Range: $800-1600
Advantages: Easy to install, dual-side measuring, portable, swappable between bikes
Disadvantages: Limits pedal choice, exposed to elements, batteries

Garmin Vector 3 power meter pedalsGarmin Vector 3 power pedals

Pedal-based power meters are less common than spider- and crank arm-based units, but are a solid option for riders who don’t want to replace or modify drivetrain components on their bike.

Older pedal-based power meters required the use of “pods” which hang off the spindle of the pedal to house the electronics. As technology has improved, so has packaging and most new power meter pedals house all the electronics within the pedals. This adds weight and a small amount of bulk to the pedal, but it is fairly discrete and will only be noticed by tech-savvy riders.

Power pedals are easy to install and remove. This is beneficial if you want to swap one power meter quickly between multiple bikes. This only applies to road bikes, however, as there is no widely available mountain bike power meter pedal on the market.

Because there is a power meter built into each pedal, they provide left and right leg power similar to spider-based and dual-sided crank arm power meters. They’re also able to display other advanced power metrics beyond left and right power like seated and standing time, platform center offset (where on the pedal you’re applying power), and phased power (how much power you apply throughout the circular pedal motion). Data-hungry riders can use this to really nerd out how their body is working, but not every rider will need that information.

However, riders will be committed to whatever cleat and pedal system the power meter is designed around. This could be an issue for picky riders or those who want the greater float afforded by Speedplay pedals. Power meter pedals may also compromise in terms of stack height, ground clearance, and q-factor, compared to their regular pedals, but new pedals from Garmin, PowerTap, and SRM are closing the gap.

Because of the power meter’s location at the pedals, it is more susceptible to damage from pedal strikes and crashes. This would be unfortunate because power pedals are likely the most expensive pedal you’ll ever purchase.

Dual-sided systems like pedals also require two batteries which can mean replacing batteries twice as often. There’s generally a slave and master pedal. The master communicates with the head unit and the slave communicates with the master. One device is doing more work so the batteries will wear at different rates.

Overall, pedal-based power meters have a smaller but growing market share. The cost is still fairly high for a small component but that may change as more options come out. They are the simplest power meter to install and a good option if you just want to buy one power meter for multiple road bikes. Advanced dynamics are also the perfect treat for the nerdiest of data nerds.

Rear Hub

Popular Options: PowerTap G3
Price range: ~$500
Advantages: Classic option, out of the way location on the bike
Disadvantages: Limits wheel/hub/axle choice, drivetrain losses can affect measurement, losing popularity

powertap g3 power meter hubPowerTap G3 hub

Hub-based power meters used to be common. In recent years, however, their popularity has waned. The way they function and measure power is similar to how spider-based power meters work because they rotate on the same axis.

However, hubs are part of the wheel. Hub-based units are less appealing these days because they constrain riders to one rear wheel. If you have a particular rim you want to use, you’ll have to custom build a wheel. If you like swapping wheels you’re limited. If you’re changing between frames, you’ll need one with the same axle and brake standards. Some riders also have particular hub preferences, and using a hub-based power meter means you can’t get fancy Chris King or Industry Nine hubs. The hubs also use bearings which can affect your power meter’s performance as they degrade.

Unlike power meters located at the cranks, they don’t measure cadence. If you’re interested in displaying cadence, hubs like the PowerTap G3 can approximate it with an algorithm that looks at power spikes. Riders experience varying levels of accuracy with this.

Hub-based power meters also measure power after drivetrain losses due to friction. All other power meters measure power before drivetrain loss.

“Depending on how clean or efficient your drivetrain is, the difference could be small or very noticeable,” Keck explains. “If your bike goes from clean to dirty, the actual wattage measured at the hub could change during a ride. Power meters that measure pre-drivetrain loss don't change as the drivetrain gets dirty.”

Hub-based power meters are still around, and many riders still ride and love classic PowerTap hubs. There’s nothing wrong with them. They are a great option to get into the power game when buying power meters on the used market. They’re just falling out of fashion with the ease of use and ubiquity of crank-based options.

Crank Spindle

Popular Options: Race Face/Easton Cinch, ROTOR INpower, Team ZWATT
Price Range: $600-800
Advantages: Discrete, hidden inside bike, broader compatibility with mountain, gravel, and cyclocross bikes using RaceFace/Easton cranks
Disadvantages: Single-side measuring, needs recharging, few crank options

Spindle-based power meters are a fairly new option. For riders using RaceFace and Easton cranks, this is a great option as it allows you to keep both of your crank arms and only swap out the spindle. Those using the carbon Next and EC90 SL cranks can maintain the low weight and aesthetics of their expensive cranks. The Race Face/Easton option is just a rebranded Team ZWATT product. The only other major option comes from ROTOR and works for their INpower cranksets.

Spindle-based units are all single-sided, similar to crank arm-based units. They measure power on the non-drive side and double it. Like spider-based units, they are tucked away in the heart of the bicycle so they are discrete and protected. The Rotor product uses a standard AA battery while the Race Face/Easton and Team ZWATT power meters use a rechargeable battery that connects to a standard micro USB cable.

Other than the brands listed here, there are no other prominent options. It is a fairly new style of power meter that may see additional development and growth in the future.

Accuracy and calibration

Power meter manufacturers make a big deal about accuracy. They generally express the accuracy of their products as within +/- X%. Accuracy is good because it means the power number you end up seeing is representative of the truth.

If you don’t have accurate power meters, then it becomes harder to objectively compare your power numbers against the numbers of other riders (the importance of this may vary depending on your goals or ego). If you ride multiple bikes with different power meters, especially if they’re from different manufacturers, your power numbers will likely be off between bikes. These are important considerations, but ultimately, the thing that is most important when using a power meter is consistency.

As long as a power meter’s readings are consistent from ride to ride, it will be useful for measuring your performance and tracking your progress. For performance-oriented riders, the most important person they need to compete with is themself.

“The holy grail of power meters is one that is accurate and consistent,” says Keck. “But really as long as what you’re using is consistent from day to day, then that’s what’s most important.”

To provide consistent information, power meters require regular calibration. For the end-user, “calibrating” technically refers to zeroing the power meter. Zeroing, or setting the "zero offset," is the equivalent of hitting the tare button on a scale. It gives your power meter an accurate starting point for measurement. All power meters have some form of zeroing or calibration associated with them. This is usually done by positioning your power meter in a neutral position and sending a calibration command with your head unit. Some power meters can also receive a calibration command through a smartphone app.

Most manufacturers recommend riders calibrate their power meters anywhere from once a week to before every ride.

“I suggest doing it before the start of every ride,” says Keck. “It’s important, especially before something like an FTP (functional threshold power) test, an important interval workout, or a race. Recalibrating often ensures your power meter is at its most accurate.”

It’s typically best to calibrate your power meter in the environment you’re going to ride in. If it’s extremely hot or cold outside, calibrate outside rather than indoors where the temperature is controlled. Manufacturers do build their power meters to compensate for temperature shifts. Quarq, for example, builds in what it calls “10K Temperature Compensation.”

“We run a power meter through a heat cycle and program 10,000 data points that help it know what impact temperature fluctuations have on the torque in the strain gauges,” Keck says. “That being said it’s nice to calibrate in specific conditions to remove as many variables as possible.”

Some manufacturers are also starting to introduce automatic calibration into their high-end power meters. These power meters calibrate themselves whenever they sense the rider is coasting and there is no strain to ensure accuracy throughout a ride.

“Quarq uses what is called ‘Magic Zero,’” Keck explains. “When you’re coasting it’ll take data and set a new zero offset. The power meter is constantly checking itself and you don’t have to manually do it anymore. It’s now available as part of our current firmware.”

ANT+ vs. Bluetooth

Power is useless unless a rider can see their power data. Most riders will view their power on a head unit (Garmin or a Wahoo are popular options) mounted to the bike. Older power meters required a wire to transmit data to a head unit but all new power meters transmit data wirelessly.

For wireless transmission, ANT+ has long been the standard, but Bluetooth Smart (or BLE/BTLE) has sprung up as an additional transmission option on most new products. Riders new to using power may wonder if they should select one transmission protocol over another.

“Historically ANT+ has been a bit more stable and trusted,” Keck says. “But Bluetooth has really improved over the last few years. Most new head units now have the ability to do both. They’re both fairly reliable now.”

Most power meter manufacturers still recommend using ANT+ simply to reduce compatibility issues. Some devices still don’t support Bluetooth Smart and some may have issues displaying power properly. If you’re curious, experiment switching between them on your own devices and see if you notice a difference. Personally, I only use Bluetooth for connecting to my smartphone or laptop for indoor training sessions.

Final thoughts

Quarq power meter Jordan Clark HaggardTraining with power | Photographer: Jordan Clark Haggard

Power meters are not cheap. But if you are committed to improving your riding performance, they are a great investment. Personally, I’ve gone back and forth between riding with and without power meters. I’m a data-driven rider who likes to see numbers. They satisfy some part of the obsessive nerd that resides deep inside me.

Power meters are an important tool for my training leading up to big target events. I recently bought an Easton spindle-based power meter for my new bike so I could prepare for the Dirty Kanza 200, the biggest race of my year. It’s allowed me to stay on target with my workouts. Seeing my power numbers improve has been key to maintaining my motivation. Also, during the race, I'll watch my power to pace my effort so that I can finish strong.

I have used several crank arm-based power meters from Stages and Pioneer in the past and had great reliability and results. If I get the opportunity to build my future dream bike, it will likely have a Quarq because it is an integrated option in the new SRAM AXS drivetrains. 

"Power meters are becoming less of an aftermarket upgrade," says Keck. "Bikes from major manufacturers are coming spec’d with them now because they've become an expected feature for serious riders. That’s why you see it a lot on a lot of Red and Force AXS drivetrains now."

For riders with the ambition and discipline to make huge improvements in their performance, a power meter is the only tool you’ll need. If you’re more interested in riding without rigid structured training, a power meter can be nice to have, but it won’t be quite as useful. Personally, I like having on even if I’m not training. It’s just fun.

Still, it is liberating at times to take a break from the numbers. When I ride without power, it allows me to disconnect from my brain a bit and reconnect with the experience of riding. Breaks like this help me remember why I love bikes so much. But I usually end up relapsing. The craving for power data always comes back.

 

Do you use a power meter or shun it? What type of power meter do you prefer? Let us know in the comments! 


2 comments


  • Hey Christian, 
    Thanks for your question. There are phone apps that can display power. It’s easiest if you can connect your power meter to your phone via Bluetooth. Stages has a phone app that will display real-time power and let you calibrate your power meter. Cyclemeter is a really popular app that essentially turns your smartphone into a cycling computer. You could mount your phone as a head unit and it will display power as long as your power meter connects. I hope that helps. 

    Bruce Lin on

  • Can the current watts data be read without a head unit hardware? Is there an app that can display realtime efforts?

    Christian EVans on


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