The Problem with Power Meters

Power meters are fantastic pieces of equipment. However, there is one huge problem with them: each one gives a different reading, and some vary wildly in their accuracy. Can power meters actually be relied upon, or are they just expensive random number generators?

Welcome 0:00
Categories of Power Meters: Pedals, Cranks & Hubs 0:25
Power Pedals & Power Cranks 2:39
Accuracy of Power Meters 3:12
Does price affect accuracy? 5:03
Can you make a power meter more accurate? 5:28
How seriously do you take your training and data analysis? 6:39
What power meter would we suggest? 7:22
Conclusions – Tell us your experience in the comments 8:04

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power meters are fantastic pieces of equipment however there is one huge problem with them and that is because each one reads differently and some of them vary wildly with their accuracy so can power meters actually be relied upon or are they just really expensive random number generators let’s [Applause] discuss if you’re new to cycling or perhaps just not a tech nerd like me this is probably a problem you’re not really aware of but it’s a problem you need to be aware of so you don’t go out and blow all of your cash on a product which doesn’t live up to your expectations also if you are new to cycling it probably means that you haven’t subscribed to gcn Tech so if you’re able to please do now then parameters fit into a number of different categories and work in a number of different ways you’ve got pedals which is the hardest place to measure as there is lots of different input forces and they’re susceptible to damage knocks and wear but the advantage is that you can swap them easily between bikes next you have cranks and spiders this isn’t as easy to install as pedals but are often more accurate and robust as a general rule the units that were designed to be power meters from the ground up rather than non-p power meter cranks then retrofited with sensors tend to be more accurate next you have the Hub which is the easiest place to measure accurately as there are far less complicated input forces but you have less flexibility in terms of your wheel choice being Downstream of the pedals and cranks the power reading can be slightly lower this is due to drivetrain losses typically around a couple of Watts they can be super reliable but not that common anymore with regards to pedals and cranks you can opt for a single-sided version which is the budget friendly option as it measures just one leg and then doubles it but these are far less accurate and physiologists believe they can lead to an imbalance between the left and right legs because you subconsciously learn to push a little bit harder with a leg that is being measured that said they are still useful if you’re on a budget and want a good idea of the power that you’re producing most brands will claim an accuracy of somewhere between plus or minus 1 to 5% however that isn’t always the case so much so that for scientific studies scientists have to be really careful with the parameters they choose to use and as a general rule fixed SGS or SRM units are what they tend to use there’s always going to be a small variation between units however some can be out by a considerable margin I mean we all seem to have that one mate on the group ride who reckons their FTP is 500 watts but we all know it definitely isn’t now this problem isn’t something new but it is a problem lots of people myself included seem to have forgotten about and I recently highlighted this in a video where I’m trying to compare heart rate against Power and the two power meters that I was using to record my efforts gave fairly different readings the power pedals gave a reading of 323 wats whereas the power crank gave a reading of 342 wat which is quite a difference over a 10 km climb on the subjects of accuracy a power meter could be inaccurate but consistent so that would mean it say reads 10 to 15 watts higher all of the time or the slope could be off this would mean that at generally lower power readings the power meter could be out by just a couple of Watts but higher power readings it could be off by say 10 to 20 wats now this is a problem especially if you have more than one power meter and you’re trying to compare your efforts on different bikes but a more common issue that we’re often asked about is where people are using an indoor smart trainer with an inbuilt parameter to do their efforts and training and then they head out onto the road using a pound meter fitted to their bike and then wonder why some of their efforts seem increasingly harder or easier than they first had planned and this is down to the difference in readings between the pales on your bike and the smart trainer indoors if you are fortunate enough to have two different Power meters it’s important you know how they track against each other to monitor this you can dual record so if you’re looking at a smart trainer and an on-bike power meter you could use two headge units to record the two devices separately and ride at varying intensity levels over different periods of time so you can do 100 WS 200 WT 300 WT 400 WTS and then throw some Sprints in the mix as well that way you can retrospectively compare how the two power meters stack up against each other now a difference of say 2 to 5 watts should be considered comparatively normal but this isn’t always the full picture because we’re just looking at recording it indoors if you were to head outside over some extreme conditions say riding over cobbles for example can make it increasingly difficult for power meters to remain accurate because of all of the different vibrations that traveling through the bike once you’re aware of all this stuff and take it into account you can then make sure that your power meter is more accurate compared to your different devices and you’re aware of it to make sure your training is as accurate as possible and it’s not price which is really affecting the different readings and accuracy of parameters because there are lots of budget friendly options out there which have been proven by lots of different people to provide accurate and reliable power meter readings and there also are some bigname Brands and expensive power meters out there which those same people have proven to be fairly inaccurate and inconsistent with their readings [Music] so what can be done about this issue well some parameters can be adjusted using specific software to allow them to update the firmware zero offset them or maybe even calibrate them now if you want to get super nerdy about it you can use some of this software to accurately calibrate your power meter this is where you hang weights of a no Mass off of the cranks but then in reality most of us are unlikely to do this however you should engage in best practice and that is to complete a zero offset before every single ride this is usually done using your head unit but confusingly some head units label this as a calibration but in reality you’re not doing a calibration it’s more like pressing the zero on a set of weighing scales it’s also worth re-zeroing your power meter if you’re doing a long ride then there is a huge change in temperature that’s because the temperature affects the strain gauges in a significant way some power meters such as those from power to Max will have automatic temperature compensation to account for this but it is just good practice to keep your power meter reading consistently it’s also worth noting that it’s important to stay on top of firmware updates so that your power meter is updated and as accurate as possible in which case is this problem really as huge as I said it is at the start of this video well it kind of depends on how serious you want to take your training and your analysis of the kind of data that you want to dive into I mean for most people provided your par meter reads consistently that is going to be more than enough for you to make improvements to your Fitness and monitor your training I mean if you plan on taking on the tour to France or you’re perhaps someone lucky enough to have two bikes and two power meters and you really want to dive to the next level of data analysis well it probably is going to be a bit of a problem for you so what would I suggest the majority of people do well I think i’ probably suggest you head out and you buy an affordable single sided power meter because I think that’s more than accurate enough to give you like a Gateway into power and make Fitness improvements and single sided power meters represent the best value for money and more than enough for what you actually need to get training with power but let’s be clear want and need are two very different things because even though I know that single Sol parameter is all that I need like many of you out there I still feel like I want something like this which is dual sided and represents the latest in technology anyway hope you’ve enjoyed this video and found it interesting to hear a different take on the differences between parameters and I am Keen to hear your thoughts on this so please do let me know in the comments section down below your experiences with parameters be that good or bad and of course if you want to see more Bike Tech related videos much like this one subscribe to gcn Tech and turn on your notifications so you don’t miss out on future uploads right I’m out of here see you later