How to Choose Between Hub-, Pedal-, and Crank-Based Cycling Power Meters
By Pro Coach Jim Rutberg
Article originally featured on powertap.com
If you’re on PowerTap’s website you are probably already interested in training with power, so I’m not going to spend your time telling you about all the ways a power meter can make your training more effective, time-efficient, and fun. Instead, let’s take a look at your choices and help you get the power meter that best fits your riding style and performance goals.
There are a lot of power meters on the market and the first step to making a choice is to make sure any meter you are considering features direct power measurement. Strain gauges are the best way to measure power because you are directly measuring the deflection caused by applying force. Some power meters try to calculate power from indirect data, but when you can use strain gauges there isn’t much point in using something less accurate.[blog_promo promo_categories=”coaching” ids=”” /]
You also have to consider both the accuracy and consistency of your data, and understand the difference between them. An accurate meter measures power within 1.5% of the actual power you are producing, but consistency is ultimately more important than absolute accuracy. Even if your power meter is measuring 2% lower than your actual power, it is important that it measures 2% low today, tomorrow, next week, and next month. Consistency is ultimately more important than absolute accuracy because it enables you to monitor your training and track your progress with confidence.
All PowerTap power meters measure power directly using strain gauges and have proven to deliver both accurate and consistent data. They all also have user-replaceable batteries and connect to a wide variety of head units. But once you decide to purchase a PowerTap, you still need to choose to measure power at the hub/wheel, chainring, or pedal. Here are some considerations to help you make your choice:
Didn’t I just say all PowerTaps are proven accurate and consistent? Yes, but that doesn’t mean they are all the same. Let me explain. Technically, for greatest accuracy you want to measure power as close as possible to the location where it is being generated. The greater the distance between generating and measuring power, the more power can potentially be lost. This would indicate that pedal-based meters are more accurate than crank/chainring meters, which are more accurate than hub-based meters. There are some special instances (research, mostly) where these differences matter. For most athletes, however, any small differences between the three options are inconsequential because consistency is still more important than absolute accuracy.
What the differences between measuring power at the pedal, chainring, and hub do illustrate is that power meters are only accurate to themselves. If you have a hub power meter on one bike and a chainring power meter on another bike, your data from one bike will be similar to but not identical to the data from the other bike. When coaching athletes who have multiple power meters on different bikes, even when the meters are both hub-based or both chainring-based, we have to be careful when comparing data between different bike/meter setups.
Before buying a power meter you have to make sure it’s compatible with the rest of your equipment. PowerTap chainrings are designed to fit on a 5-bolt, 110bcd crank. View compatibility chart. The P1 pedals use a 3-bolt Look-style cleat, so you will need road cycling shoes that are compatible (the vast majority are). If you are looking to measure power on a mountain bike, you need to go with the PowerTap hub built into a mountain bike wheel. And any athlete considering a rear wheel or wheelset option needs to check their bike for the following information: axle spacing, disc vs. rim brake, and quick release vs. thru axle. If you use a wheel-off trainer that is not a smart trainer (doesn’t contain a power meter in the trainer), you will need to record power using a C1 or P1.
A lot of athletes train on more than one bike and in an ideal scenario you would train with power on all of them. On a scale of time and tools required, swapping PowerTap wheels from one bike to another is fast and requires no tools, although you may need to change tires. PowerTap P1 pedals are easy and fast to swap between bikes and will thread into any standard crank. You only need an 8mm Allen wrench to get the job done. The most time-intensive swap is moving a C1 chainring setup from one bike to another. Even so, it is still a simple process involving only 5 chainring bolts.
The table below summarizes the compatibility of PowerTap’s hub, chainring, and pedal power meters across a range of bikes.
From a practical standpoint, I would make the following recommendations. If you only ride in road shoes and/or travel frequently, P1 pedals are the easiest and quickest option and you can pop them onto a rental road bike or even a hotel exercise bike on a business trip. If cyclocross and/or gravel are a big part of your life, a C1 chainring is a great option because you can use it with either road or MTB shoes, and with a variety of wheels. And PowerTap wheel options are great if your bikes have a variety of crank bolt patterns (4-bolt/110bcd, 5-bolt/130bcd, etc.), you want to use different chainring sizes on different bikes, or you want to build up a really slick set of carbon wheels for training and racing!
No product lasts forever, but PowerTap power meters have a great track record for durability. Even so, it is good to at least think about long-term wear and tear before making a purchase. Hubs with cartridge bearings are pretty much bullet-proof when it comes to wear. You’ll have to change batteries and eventually replace the bearings, but the rim will give out well before the hub does. On the C1 you will eventually have wear on the chainrings themselves, especially if you are not good about keeping your drivetrain clean and replacing your chain with reasonable frequency. Fortunately, the chainrings are replaceable at a fraction of the cost of a new power meter. P1 pedals are also extremely durable. The only thing to keep in mind is that, of the three options, the pedals are most susceptible to impact damage if you crash or smack your inside pedal into the road while pedaling through a turn.[blog_promo promo_categories=”bucket list” ids=”” /]
5. The Big Picture
A power meter is a long-term investment in your progress as an athlete. There will always be a cheaper option, but in the long run athletes are best served by shopping on value over price. After 15 years of training athletes with power, the value you are paying for is the years of testing, product refinement, and quality control. And don’t underestimate the value of buying from an established company with the customer service and production infrastructure to be responsive to customers’ needs. If you bought a car from a company that just started making cars and the car frequently needed repair from an understaffed and inexperienced service department, you’d get frustrated pretty quickly. If you just want to use your power meter instead of futzing with it, buy a PowerTap.
Jim Rutberg is a Pro Coach with CTS and the co-author of 8 books on training and sports nutrition, including “The Time-Crunched Cyclist”. He is also a 10-time finisher of the Leadville 100 MTB Race and 2-time finisher of the Dirty Kanza 200 gravel race. For more information on personal coaching, training camps, and CTS Bucket List events, visit www.trainright.com.
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Hi – I have been using Stages spin bikes (with stages crank arm). How comparable will these be to other set ups that are being used through Zwift? Does Zwift have any impact on FTP/watt readings or is it just the output and the bike setup/calibration of power meter are the most important?
I currently run a quarq elsa RS on my cannondale and was looking to add power to my Giant tcr.. Was looking to add a stages left arm PM but wondering if it makes sense to do the investment as i must admit i ride the cannondale more than the TCR due to it having the Power Meter.
The cannondale is compact whilst the TCR is standard 53/39. Need some quick advice. Want to know if the data will be comparable enough where it is useful or i should continue to ride without power and find something more useful to spend the funds on.
If consistency is more important than absolute accuracy, then an iBike Newton is every bit as good a choice as any strain gauge power meter. Plus, it’s completely portable to any bike. Just add another user profile. Too bad this is was simply an infomercial for Powertap.
I too thought this would be informative instead of just an infomercial for PowerTap. Very disappointing. I don’t disagree with much of what is said, but the title of the article is very, very misleading.
My SRM is now going one 1 year. It got me through IM training and IMLP. I love it, but it has 2 downfalls. I am dreading the day when I need to send it back for batteries, and I wish I could afford another for my road bike…
This article talks about durability of the powertap hub. I have found that the guts of the hub itself are solid. However, mine is now two years old and I have had to replace the freehub twice and the rim is now cracking at the spokes, I’m not so sure that I call that dependable. I have two bikes, and don’t switch the wheel between them so I only use the powertap bike a little over half the time. My Campy Euros wheelset are stiffer, more responsive and don’t keep breaking down.
I have been using an IBike Newton+ for years. This opposing force power meter is every bit as accurate as any strain gauge power meters. Just get a power meter and learn how to use it. And if you are any more anal than that you got your head up your ass.
Other than the “infomercial,” I find this beyond useless. I have two PowerTaps at present on two bikes. One’s an old 9-speed Campy, the other an 11-speed (about 7 years old, now!). The “new” G3 power meter has bearings/freewheel failing – second time in two years. I’m looking for something that fits SPD-SL pedals and Campy chainrings – and PowerTap doesn’t answer either. And I’m not switching all my bikes to Look, just to use a pedal power meter!
Have you checked out Garmin Vector 2, and the Shimano conversion kit? Since these are pedal based, you can use a Campy crank (I do). And while you’ll be buying Garmin Look-compatible pedals, you’ll be able to swap the insides over to Shimano Ultegra compatible pedals (I don’t know – are Dura Ace pedals compatible w/Ultegra?).
If you’d like to continue using Shimano SPD-SL pedals and a Campy crank/chainrings, Colin is correct in that Garmin makes a conversion so you can use SPD SL with Vector pedals. The other, albeit much more costly, option is getting a Campy SRM. – Jim Rutberg, CTS Pro Coach
Charlie – +1 on the Garmin Vector 2… they now have a conversion kit so you can move the spindles over to the bodies of a Shimano SPD SL pedal – the 6800 carbon bodied Ultegra model (to be exact – DuraAce have a second set of bearings so the conversion will *NOT* work w/ DA peals). I’ve just installed the setup, did the swap of innards myself, and have a week or so on the system… happy so far! Curious to see how the cycling dynamics info can assist w/ improving my form/smoothness. (Hint hint – Jim R – how about an article on how to leverage this info!) Haven’t moved the system to a different bike yet but may do so to my fixie this weekend. The Vector 2 is *much* easier to install than the first version.
Have to agree that this seems to be an undisguised infomercial. From the title I expected something more. Would like to have learned specifically the differences, pros and cons, of the top power meters on the market, particularly SRM and Quarq, the ones I have on my two bikes.
Powertap asked me to write an article to help athletes choose between measuring power at the hub, pedal, or crank/chainring. They published it on their site and we decided to publish it on our site as well. The factors discussed should be considerations when looking at any power meter brand. When it comes to SRM and Quarq, for instance, you have the benefit of being able to run any pedals and wheels you want. You can also put your bike on a wheel-off trainer and still use your power meter (although most wheel-off trainers are smart trainers), or use a traditional wheel-on trainer and still use your power meter. Portability is a bit of a pain with both, in that you have to move the entire crank assembly between bikes (which can lead to compatibility issues regarding bottom brackets). However, you can also change the chainrings on both, so you can go from a road setup to a cyclocross setup. – Jim Rutberg, CTS Pro Coach
Although I did read the whole article, the statement at the top (originally featured on powertap.com) pretty much admitted that this was going to be a thinly disguised infomercial. The sentences “Strain gauges are the best way to measure power because you are directly measuring the deflection caused by applying force. Some power meters try to calculate power from indirect data, but when you can use strain gauges there isn’t much point in using something less accurate.” totally exposed your bias. Correct me if I am wrong, but do you not receive compensation, in the form of equipment use, if not money, from a direct force power meter company?
Please stick to coaching and leave gear review to those who employ engineering analysis can maintain objectivity in their conclusions. I’ll get my gear review from DC Rainmaker from now on.
I’ve read some of DC Rainmaker’s reviews on power meters and he isn’t always objective either, particularly in his data analysis.
Regardless of the products being compared, I stick by the statement that direct measurement with strain gauges is preferred over indirect measurement. You can find strain gauges in power meters from Powertap, SRM, Stages, and Garmin, to name a few. – Jim Rutberg, CTS Pro Coach.
KNOWN FOR THEIR ATTENTION TO EVERY DETAIL OF THE TRAINING AND RACING PROCESS, TEAM SKY RELIES ON STAGES CYCLING TO PROPEL THEM TO VICTORY.
TEAM SKY RIDES
” Years on Stages: 2
After extensive testing and validation, Team Sky chose to exclusively use the Stages Power meter in 2014. In 2015 they continue to choose and ride Stages Power.
Team Sky rides on a Stages Power meter applied to a Shimano Dura-Ace 9000 series crank. The meter’s ultra-lightweight, and seamless integration with the top-of-the-line Dura-Ace 9000 series, adds a mere 20 grams of weight, without disrupting the integrity of Shimano’s premium drive side crank and chainring configuration.”
Team Sky uses a Stages power estimator for 1 reason and that’s because Shimano pays them big dollars through their sponsorship of the team. So they have to use a power estimator that is compatible with Shimano.
I’m sure you are right that Team Sky uses Shimano because they get paid for it. If you notice Carmichael has a sponsorship or they might call it a partnership with powertap and so why would you expect anything other than an infomercial?
As one who owns 2 PT hub based meters and 1 stages , Powertap is the hands down winner for consistent reliable data . The Stages has problems with fast high force calcs , sprint numbers are too high . Great customer service at Powertap as well .