Power meters are available in a variety of forms and there’s a lot to think about when considering which one to invest in. There is, however, a key difference between the InfoCrank and all other power meters – here’s what you need to know.
What does a power meter measure?
So what does a power meter actually measure? Power is a product of torque x cadence:
Torque is a measure of how much force is acting on the pedal causing it to rotate, i.e. the tangential force per pedal stroke.
Cadence is the speed at which the pedal is rotating around.
Torque x cadence = power (watts).
Direct measurement vs algorithms
Torque can only be accurately measured from the cranks of the bike. Other positions – such as pedals, hubs and spiders – can measure some of the many forces that are applied to make the bike go, but the tangential force, which drives the bike forward, is applied only to the crank.
This fact is really important. It is the distinction between direct measurement (with the InfoCrank) and mathematical algorithmic calculations – the other power meters. The InfoCrank measures torque from within the crank arms at a rate of 256 times per second to provide a true, precise and completely comparable result, regardless of temperature, road surface, slope and all the other variables inherent in bike riding.
The other devices are measuring force somewhere on the bike and then using mathematic algorithms to deduce what they believe the power number to be. Therefore they can be very good at averages and overall output, however the problem is that improvement in anything does not come out of averages, but out of specifics.
Calibration for life or as often as possible?
Being built to measure the right force in the right place means that the InfoCrank power meter does not need constant calibration or zeroing. This happens at the factory and just as the crank maintains the same shape for life, the calibration is also for life.
Zeroing after battery changes is recommended, because a surge is introduced into the system. However, nothing more is necessary. Every other time you ride, you simply pair your InfoCrank with your head unit and ride.
This contrasts with all the other devices, which tell you to calibrate as often as possible – even when running late for that group ride! But when a measurement device itself needs on-going calibration, how can you trust it? When does it start to ‘go off’? At the end of the ride or closer to the beginning? You have no way of knowing. If you are like us, you don’t want to fiddle with equipment constantly to make it work. You want to get on your bike and ride.
So consider what you’re looking for in a power meter – do you want accuracy you can trust or an estimation based on algorithms? Do you want the simplicity of having a power meter that is already calibrated for life or do you want a power meter that requires constant calibration?
Get in touch if you’d like to talk to our experts about which InfoCrank is right for you.
Want to know why the InfoCrank is the most accurate power meter in the world?
This three-part video series covers the 2% myth (the accuracy claim made by numerous power meter devices currently on the market) as well as what validity is, what reliability is and why they are important if you want to be able to trust the data from your power meter.
The series is hosted by Brad Hall, Managing Director of both the Veris Racing team and the Exercise Institute, based in Perth, Australia.
Part one of Brad’s guide to what’s important when it comes to the accuracy of your cycling power meter highlights what you need to consider if you’re thinking of investing in one. This episode reveals the 2% myth – the accuracy claim made by numerous power meter devices currently on the market.
Part two of Brad’s guide to power meter accuracy demonstrates why the InfoCrank is the only power meter you can trust. In this episode, Brad talks about why validity is important and needs to be considered if you’re thinking of investing in a power meter.
The final part of Brad Hall’s three-part series looks at reliability and what you should look for if you truly want to be able to trust the data from your power meter. Brad covers all in this last installment.
A simple way to look at accuracy is from the bottom up. Most people can intuitively grasp the idea that if the original measurement is not accurate then everything that follows from that is going to have a widening degree of error. Measuring forces, and then translating those forces into a wattage number that so many coaches and athletes find useful, is a case in point.
The InfoCrank is a torque transducer. It measures crank torque 256 times every second throughout the exercise whether the crank is turning or not. The targeted aim of the InfoCrank is to achieve 0.5% error maximum at any revolution, so we can work backwards to find out how accurately we need to measure the torque.
Below is a visualisation of four pedal strokes. There’s one wave for each leg, both with measurements of torque at 256 times per second. For a normal pedal stroke, a cyclist pedals at something between 60rpm and 90rpm. Good cyclists pedal faster with the top track riders often between 150rpm and even over 200rpm.
As you can see, there is a huge range of possibilities that need measurement. In this case, the top torque on a pedal stroke was 86.5541nm and only 0.8secs later the lowest point was recorded on that pedal stroke of -13.0476nm. The measurement has to be within the maximum error margin that entire time and also trace the shape – hence the high speed reading.
If we accept that the electronics themselves will allow some error to creep in, we want to be able to measure torque more accurately than the maximum error allowed, so let’s assume that we aim to be accurate to 0.25 watts.
Firstly, what would most people think that means? For the average cyclist, they would think that if I said the InfoCrank measured to 0.5% accuracy it would mean that if their bike computer showed 200w, then they know that their actual wattage is between 199.5watts and 200.5watts. So to be sure of achieving that, we need to measure the base measurement – crank torque throughout the entire curve of each pedal stroke at a certain maximum level of error.
Since the higher the speed of crank rotation actually increases the wattage error for the simple reason that watts = torque X speed of crank rotation, we need to read accurately at the highest crank rotations and let the low ones look after themselves. Once again, the maths tells us simply that to be accurate in wattage (allowing for error in the electronics beyond the actual measurement) we need to read each torque signal at least at 0.016nm if we assume that the maximum rotation is 150rpm.
A key part of the measurement system is the Analogue to Digital Converter (ADC). The best in the world currently is a 20-bit converter with an ‘accuracy’ of +-5ppm. It is deemed suitable for:
High speed data acquisition
Portable or compact instrumentation
Industrial process control
Low power battery-operated instrumentation
This is the type of product that is needed after precise placing and bonding of strain gauges to read the signals with the accuracy needed to ensure that the wattage errors can remain below 0.5%. Now to put this into perspective. If you wish to buy one of these for each crank, as long as you buy more than 100 at a time, they will only cost about $41 USD each.
Considering that one of the leading selling power meters sells to the bike manufacturers for about $75, you can guess that they are not using top components. By the way, a quick check of the ADC marketplace shows some 8-bit ADC with accuracy at +-2% – sound familiar? You’ll see this claim repeatedly made about power meters that use cheaper components and retail for around $300.
Of course, most people think that it is all in the strain gauges, but that is another story. Not much use using top quality strain gauges if you cannot read with high definition. Which leads us onto the final question, what is your power meter worth? If you want to install more than a gimmick to your expensive road bike (which you have no doubt spent months researching), then spend a fraction of that time understanding the truth of power-measurement and do yourself and the road bike justice.
Indoor cycling now incorporates a fully-fledged competitive domain and has somewhat inevitably followed the well-trodden human path of play becoming game becoming sport. The fundamental nature of sport is debated, but it is in part the process of formalising play just enough to preserve both a sense of fairness and the necessary unpredictability of outcome. This process benefits participants and spectators alike, since if the outcome of sport is either predictable or grounded upon inequity then it ceases to be fun, which is the fundamental nature of play.
But to borrow some legal terminology, has this transformation from indoor cycling to virtual racing occurred mutatis mutandis? That is, has all necessary formalisation been considered and included on the road between play and sport?
Whilst high-profile virtual racing events take place in a singular location including both participants and spectators, by its very nature virtual racing usually occurs in a global network of self-funded pain-caves, interconnected by online platforms such as Zwift. This fortunate convergence of technology has enabled a new order to emerge out of the chaos, and in some ways has revolutionised what we think of as cycle-sport. But many participants and spectators are already sensing unease regarding the question of in-race power validation, which threatens to undermine the sport’s credibility.
As in any new market, there is a proliferation of brands vying for market share by creating the best products they can and which they think the participant needs to enjoy his or her pastime. Also as in any new market, there is much that is different between these products and therefore much room for an unintentional reduction in fairness or too much unpredictability to creep back in and erode trust in those at the top of the leaderboard.
When Pain Cave A represents 280W on-screen for an actual rider effort of 300W, and Pain Cave B represents 300W on-screen for an actual rider effort of 280W, we can see how Rider A becomes very quickly disadvantaged.
It is easy at this point to resort to scientific claims about this and that, but in the spirit of collaboration we can attempt to conceptualise the above challenge in terms we can all agree on. Watts is the unit of power and is the result of measuring objective quantities such as metres and kilograms and then accurately mapping these measurements against time in seconds – legs having both extension (size) and mass and moving in circles at certain speeds are fundamentally analysable within these terms.
There is therefore an objective and correct fact-of-the-matter about how much power a cyclist produces and we can in some sense call this The Truth. Whereas the cyclist experiences The Truth as effort, it is the sports scientist who represents, or more accurately Re-Presents The Truth to themselves mathematically and conceptually.
But if we can say that we’re all interested in The Truth, what then of the variation in numbers displayed by differing power meters? This is sometimes characterised as a difference in degree of accuracy. Yet Accuracy, unless carefully characterised, is not really something that admits of degrees – to say something is 2% accurate is actually in some sense conceptually incoherent. This is because the Accuracy of any stated value relies on the underlying measurements generating those values having two aspects, the measurements must be both:
True – The measured quantity is as close as possible to that quantity’s actual value, and;
Precise – The degree to which two or more repeated measurements show the same results each time.
It is possible for measurements to be True and not Precise, just as my stopped clock may tell the right time twice a day. It might happen to be six o’clock when I check but this is simply coincidence. Equally, it is possible for measurements to be Precise and not True, just as my clock always being set 15 minutes behind, unless I am aware of this I will always be late for my meetings.
Where the Infocrank excels is that its measurements are both True and Precise. To extend the analogy, it is in effect an operational clock that is set at the correct time. When I look at the clock I can know that what I am seeing is an accurate Re-Presentation of The Truth, that is the actual time.
For Accuracy to admit of degrees the way in which the measurements are being taken must in principle be able to converge to True, assuming sufficient sensitivity of the measuring device. Measuring some kind of causally associated yet distant change within the cycling drivetrain (such as deflection in the spider or the tension in the chain) and processing the measurements to generate the power numbers cannot be said to be Accurate, simply because it is not possible in theory for such a measurement to converge to True.
Only when measurements are taken directly, that is of the literal force applied by the cyclist on the pedal down-stroke measured as crank-arm deflection, can the measurement in theory converge to True, and therefore stand a chance of being Accurate. Everything else is some measurement or other run through an algorithm, and this is what you actually see on your graphs, but InfoCranks do not need to conceal the lack of True with an attempt to secure Precise. This is why we can talk in terms of percentage of error from The Truth.
For another view consider the words of Sports scientist and coach, James Spragg, in Cycling Weekly recently: “Before virtual racing came along, power meters needed to be relatively accurate to themselves, to use as a training gauge. As a training tool they work fine. But when you start comparing the values from a Stages crank to an SRM then you start to get issues. Because they were never designed to do that…. Between two SRMs you could have an eight per cent swing. Between two Stages power meters you could have a 12 per cent swing,” he says, referring to data from the 2017 study. This expresses the challenge faced by virtual racing in an alternative way.
Spragg makes a similar point to Verve, but as we have seen already Accuracy has two components, True and Precise. We can therefore see the common misconstruction mentioned earlier expressed in Spragg’s words “power meters needed to be relatively accurate to themselves”, which means on the most charitable reading Precise and which we now understand is only one of the aspects necessary for Accuracy to even be possible. This is why many claims about 2% Accuracy are nonsensical, because they are not being made in relation to The Truth. Most would now concede that “Accurate to themselves” is synonymous with ‘uniformly and consistently wrong’.
What is needed then is a benchmark, and in virtual racing the benchmark has to be accurate power numbers, or the objective and correct fact-of-the-matter, or simply the Truth. Top eSports team Canyon ZCC chose Infocrank precisely because Verve are in the business of truth, and we are playing our part in preserving the sense of fairness and unpredictability of this new discipline, but we understand that more is needed.
This isn’t a difficult problem to solve, in fact it already has been, but what is required first is helping others to understand what Accuracy really is, not what they are told it is. At Verve we firmly believe that the truth is always out there and rarely any more than one step away if you know where to look. So, back to the original question, has indoor cycling’s transformation to virtual racing occurred mutatis mutandis? Quite simply, no, but it is happening more quickly with the help of Infocrank.
In the world of competitive cycling and coaching many things are said about the accuracy of power meters. What is acknowledged by all is that knowing and training the power of the athlete is the single most important determinant for success. The energy (watts) expended by the cyclist in driving the bicycle forward determines everything else.
But confusion runs rampant and logic is totally lost due to the misinterpretation of the simple word – accuracy.
Most athletes and their coaches try to explain accuracy in terms of consistency. They say that the only thing that matters is that the results from their power meter are somewhat consistent.
In this case, half right is totally wrong. It is logically impossible to know (as an athlete or coach) if your power meter is consistent if you do not know if it gives true results. That is why the actual definition of accuracy is defined as having two parts:
Trueness. – is the closeness of a measurement quantity to that quantity’s true value. In other words, it is the extent to which the measurement is error free.*
“Precision” – is the degree to which two or more repeated measurements show the same results each time. Sometimes precision is referred to as the reliability or consistency of the measurement.*
It is possible if you have extensive testing facilities to determine whether your device shows consistent results, without necessarily ever showing true results. But for the cyclist on the road and the coach looking at results, it is impossible.
With the advent of the InfoCrank, acknowledged as the power device that is both true and precise the whole time, there is a sea change about to happen. The InfoCrank has been independently tested for both torque (measured 256 times each second) and for power (watts) which combines the torque and the cadence to a level of accuracy (both parts of the definition) that in simple terms, the number on the screen of the athlete is always the correct wattage number.
For the first time, leading federations and coaches are realising that they now have a tool to help with selection of athletes for teams. Because they have trueness and precision all the time on every bike, they can directly compare each athlete and make selections accordingly.
Many commentators may have assumed that this was happening before, but it was not the case. Some federations knew that their devices were quite consistent, but not directly comparable bike to bike or rider to rider. This has now changed.
However, some competitive amateurs also knew it, but not because of expensive measurement tools. Riders who use certain indoor spinning machines with a crank based power device go to extremes to mark their favourite machine. They have learned that their perceived effort differs machine to machine and has no relationship to the number being shown on the head unit.
A break-through is now easily predictable. Over the next years, say leading up to the Tokyo Olympics, there will be very significant improvements in cycling performance and not because of the chemists and doctors.
With only consistency (at most) to go on, it was quite a random exercise to have anyone other than podium athletes really train at the specified level. The data was only viewed after the event, so normally only averages were observed. As the cyclist changed bikes from the road to the track or vice versa, the numbers differed greatly as they did in different environments.
The Cyclist did not know as they rode their intervals how closely they were maintaining their workload and so nearly all riders, even with all the technology available, have been training on Perceived Effort with numbers to prove it. This is why well-known professional riders say they do not ride with their power meters. They are very well tuned to Perceived Effort and the power estimator does not add particular value to them.
Have a look at the 50 second excerpt below from a steady ride (on a real climb) where the athlete was attempting to maintain 250 watts. The InfoCrank showed the right number each pedal stroke as it has been independently tested to do.
The other power device (claimed to be accurate to 1.5%) showed numbers that varied second by second in a 100 watt range, both negative and positive. For the rider who wants to measure his effort, he truly has no idea what power is being ridden.
Many coaches might be satisfied with the uploaded data after the event, because after all the fluctuations, the average result is OK. The rider, the one who is riding the effort in order to improve, never had any idea what pace he was riding and does not know until later.
No wonder that professional riders when asked what they want from a power meter, say simply, “ I just want the right number”.
The advances in cycling performance will come from a combination of things that follow from having true and precise numbers all the time.
Firstly, the Bio Feedback loop, (what the legs are feeling, what the head unit is showing and what the eyes are seeing) will enable the athlete to control their efforts more closely than just by using Perceived effort and power estimations.
This in turn will enable controlled breakthroughs in thresholds and improvements in maintaining them. The coaches will be key here as they adapt from averages to true numbers.
The pedal stroke itself will come in for significant improvement as that same feedback loop uses the intra-pedal stroke accuracy to voluntarily improve individual muscle performance and train fine motor skills. The biomechanics, the bike fitters, the physiologists will all be key here as they ensure that the rider and the machine are optimised for his/her event.
All that will need to have to happen for a quantum leap in cycling performance to occur is to listen to the riders – They want the right (true) number and they are getting the point!
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