Cycling power meter
Encyclopedia
A cycling power meter is a device on a bicycle
that allows measuring of the power
output of the rider. Most cycling power meters use strain gauge
s to measure torque
applied, and, combined with angular velocity, calculate power. The Technology was adapted to cycling in the late 1980s and was tested in professional bicycle racing i.e.: the prototype Power Pacer (Team Strawberry
) and by Greg LeMond
with the SRM device. This type of power meter has been commercially available since 1989. Power meters using strain gauges are mounted in the bottom bracket
, rear freehub
, or crankset
. Certain newer devices do not use strain gauges and instead measure power through handlebar-mounted units that utilize the principles of Newton's Second Law by measuring a cyclist's opposing forces (gravity, wind resistance, inertia, rolling resistance) and combining these with velocity to determine the rider's power output.
Training using a power meter is increasingly popular. Power meters generally come with a handlebar mounted computer that displays information about the power output generated by the rider such as instantaneous, max, and average power. Most of these computers also serve as all-around cycling computers and can measure and display heart rate as well as riding speed, distance and time. Power meters provide an objective measurement of real output that allows training progress to be tracked very simply—something that is more difficult when using, for example, a heart rate monitor alone. Cyclists will often train at different intensities depending on the adaptations they are seeking. A common practice is to use different intensity zones. When training with power, these zones are usually calculated from the power output corresponding to the so called lactate threshold or MAP (maximal aerobic power).
Power meters provide instant feedback to the rider about their performance and measure their actual output; heart rate monitors measure the physiological effect of effort and therefore ramp up more slowly. Thus, an athlete performing "interval" training while using a power meter can instantly see that they are producing 300 watts, for example, instead of waiting for their heart rate to climb to a certain point. In addition, power meters measure the force that moves the bike forward multiplied by the velocity, which is the desired goal. This has two significant advantages over heart rate monitors: 1) An athlete's heart rate may remain constant over the training period, yet their power output is declining, which they cannot detect with a heart rate monitor; 2) While an athlete who is not rested or not feeling entirely well may train at their normal heart rate, they are unlikely to be producing their normal power—a heart rate monitor will not reveal this, but a power meter will. Further, power meters enable riders to experiment with cadence
and evaluate its effect relative to speed and heart rate.
Power meters further encourage cyclists to contemplate all aspects of the sport in terms of power because power output is an essential, quantitative link between physiological fitness and speed achievable under certain conditions. A cyclist's VO2 max
(a proxy for fitness) can be closely related to power output using principles of biochemistry, while power output can serve as a parameter to power-speed models founded in Newton's laws of motion
, thus accurately estimating speed. The joint application of power meters and power models has led to increasingly more scientific analyses of riding environments and physical properties of the cyclist, in particular aerodynamic drag.
by ANT. Currently, Garmin
, Quarq, SRM (Schoberer Rad Meßtechnik
) and PowerTap have deployed this interface for various purposes on the bicycle.
power meters measure the torque
applied to both pedals via strain gauge
s positioned within the crank spider. A calculation of power is derived from the deflection of the strain gauges and pedaling cadence
.
These units require specific cranksets, but can be relatively simple to interchange between bikes depending on compatibility.
power meters rely on the torsional deflection in the BB shaft, this is done by the shaft having a disc at each end with perforations, these perforations are detected using non-contact photo-electric sensors that detect when torque is applied to the left pedal and then doubled. Data is sent digitally to a handlebar
mounted computer unit.
These units are difficult to interchange and require a different bottom bracket unit for each bike. The only company producing such systems, Ergomo, went into liquidation in 2008.
power meter uses the same strain gauges that are present in the crank power meters but are located in the rear wheel hub and measure the power after the drive chain, because of this, power should theoretically be measured less than the crank based power meters.
Because these units are built into the rear wheel it is simple to interchange between bikes as long as the wheels are compatible.
units is essentially a guitar pick-up that mounts to the cycle's chain stay.
With this system the pick up detects the chain vibration and speed and mathematically converts it to a power output.
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
that allows measuring of the power
Power (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
output of the rider. Most cycling power meters use strain gauge
Strain gauge
A strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
s to measure torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
applied, and, combined with angular velocity, calculate power. The Technology was adapted to cycling in the late 1980s and was tested in professional bicycle racing i.e.: the prototype Power Pacer (Team Strawberry
Team Strawberry
Team Strawberry was a professional bicycle racing team that participated in experiments on human power/performance conducted by their primary sponsor, Balboa Instruments of Newport Beach, California. The Team was founded in 1988 by team captain Alan R. McDonald...
) and by Greg LeMond
Greg LeMond
Gregory James LeMond is a former professional road bicycle racer from the United States and a three-time winner of the Tour de France. He was born in Lakewood, California and raised in Reno, Nevada....
with the SRM device. This type of power meter has been commercially available since 1989. Power meters using strain gauges are mounted in the bottom bracket
Bottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
, rear freehub
Freehub
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism, and the name freehub is a registered trademark of Shimano. A set of sprockets are mounted onto a splined shaft of the freehub to engage the chain...
, or crankset
Crankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...
. Certain newer devices do not use strain gauges and instead measure power through handlebar-mounted units that utilize the principles of Newton's Second Law by measuring a cyclist's opposing forces (gravity, wind resistance, inertia, rolling resistance) and combining these with velocity to determine the rider's power output.
Training using a power meter is increasingly popular. Power meters generally come with a handlebar mounted computer that displays information about the power output generated by the rider such as instantaneous, max, and average power. Most of these computers also serve as all-around cycling computers and can measure and display heart rate as well as riding speed, distance and time. Power meters provide an objective measurement of real output that allows training progress to be tracked very simply—something that is more difficult when using, for example, a heart rate monitor alone. Cyclists will often train at different intensities depending on the adaptations they are seeking. A common practice is to use different intensity zones. When training with power, these zones are usually calculated from the power output corresponding to the so called lactate threshold or MAP (maximal aerobic power).
Power meters provide instant feedback to the rider about their performance and measure their actual output; heart rate monitors measure the physiological effect of effort and therefore ramp up more slowly. Thus, an athlete performing "interval" training while using a power meter can instantly see that they are producing 300 watts, for example, instead of waiting for their heart rate to climb to a certain point. In addition, power meters measure the force that moves the bike forward multiplied by the velocity, which is the desired goal. This has two significant advantages over heart rate monitors: 1) An athlete's heart rate may remain constant over the training period, yet their power output is declining, which they cannot detect with a heart rate monitor; 2) While an athlete who is not rested or not feeling entirely well may train at their normal heart rate, they are unlikely to be producing their normal power—a heart rate monitor will not reveal this, but a power meter will. Further, power meters enable riders to experiment with cadence
Cadence (cycling)
In cycling, cadence is the number of revolutions of the crank per minute; roughly speaking, this is the rate at which a cyclist is pedalling/turning the pedals...
and evaluate its effect relative to speed and heart rate.
Power meters further encourage cyclists to contemplate all aspects of the sport in terms of power because power output is an essential, quantitative link between physiological fitness and speed achievable under certain conditions. A cyclist's VO2 max
VO2 max
VO2 max is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual...
(a proxy for fitness) can be closely related to power output using principles of biochemistry, while power output can serve as a parameter to power-speed models founded in Newton's laws of motion
Newton's laws of motion
Newton's laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces...
, thus accurately estimating speed. The joint application of power meters and power models has led to increasingly more scientific analyses of riding environments and physical properties of the cyclist, in particular aerodynamic drag.
Interfaces
Most cycling power meters use a set of wires to transmit power information to a computer mounted on the bicycle; this system has a serious disadvantage of having fine electrical cables being run all over the bicycle, making it harder to clean as well as using a fair number of fasteners to hold them up. However as of late 2008/early 2009, there is a general trend to move towards wireless systems . A popular wireless system is ANT+ANT+
ANT+ is an interoperability function that can be added to the base ANT protocol...
by ANT. Currently, Garmin
Garmin
Garmin Ltd. , incorporated in Schaffhausen, Switzerland, is the parent company of a group of companies founded in 1989 by Gary Burrell and Min Kao , that develops consumer, aviation, and marine technologies for the Global Positioning System...
, Quarq, SRM (Schoberer Rad Meßtechnik
Schoberer Rad Meßtechnik
Schoberer Rad Meßtechnik , or Schoberer Rad Messtechnik, is a company which created the first mobile ergometer for bicycles. Formed in 1986 by Ulrich Schoberer, the name literally means "Schoberer’s bike technical measurement." The SRM Powermeter uses built-in strain gauges to determine the power,...
) and PowerTap have deployed this interface for various purposes on the bicycle.
Crankset
CranksetCrankset
The crankset or chainset , is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain, which in turn drives the rear wheel...
power meters measure the torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
applied to both pedals via strain gauge
Strain gauge
A strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
s positioned within the crank spider. A calculation of power is derived from the deflection of the strain gauges and pedaling cadence
Cadence (cycling)
In cycling, cadence is the number of revolutions of the crank per minute; roughly speaking, this is the rate at which a cyclist is pedalling/turning the pedals...
.
These units require specific cranksets, but can be relatively simple to interchange between bikes depending on compatibility.
Bottom bracket
Bottom bracketBottom bracket
The bottom bracket on a bicycle connects the crankset to the bicycle and allows the crankset to rotate freely. It contains a spindle that the crankset attaches to, and the bearings that allow the spindle and cranks to rotate. The chainrings and pedals attach to the cranks...
power meters rely on the torsional deflection in the BB shaft, this is done by the shaft having a disc at each end with perforations, these perforations are detected using non-contact photo-electric sensors that detect when torque is applied to the left pedal and then doubled. Data is sent digitally to a handlebar
Bicycle handlebar
Bicycle handlebar or often bicycle handlebars refers to the steering mechanism for bicycles; the equivalent of a steering wheel. Besides steering, handlebars also often support a portion of the rider's weight, depending on their riding position, and provide a convenient mounting place for brake...
mounted computer unit.
These units are difficult to interchange and require a different bottom bracket unit for each bike. The only company producing such systems, Ergomo, went into liquidation in 2008.
Freehub
A freehubFreehub
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism, and the name freehub is a registered trademark of Shimano. A set of sprockets are mounted onto a splined shaft of the freehub to engage the chain...
power meter uses the same strain gauges that are present in the crank power meters but are located in the rear wheel hub and measure the power after the drive chain, because of this, power should theoretically be measured less than the crank based power meters.
Because these units are built into the rear wheel it is simple to interchange between bikes as long as the wheels are compatible.
Chain
At the heart of chainBicycle chain
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics. Nickel also confers a measure of...
units is essentially a guitar pick-up that mounts to the cycle's chain stay.
With this system the pick up detects the chain vibration and speed and mathematically converts it to a power output.