Power Meter Comparison – PT P1 Pedals, PT Hub, Stages

I purchased my first power meter in 2009… a rather pricey (at the time) PowerTap hub as part of a wheel build from Wheelbuilder.  I’m a big fan of training and racing with power meters, as they really help quantify your actual output.  They don’t care about fatigue, wind, temperature (assuming temperature compensation), hydration level, etc… they simply give you the (sometimes) harsh reality of what your body is actually producing for power and work.  Combined with a good training program like TrainerRoad, they can help you significantly improve your cycling speed over time.

Over time I’ve used several PowerTap hubs, most of which have been purchased used on eBay.  I’ve really had nearly no trouble with the hubs, other than some brake rub caused by the very first hub I purchased.  The unit has performed flawlessly from a power measurement standpoint, but I had purchased a “low weight” alloy axle model, that proved to have too much flex in the hub when I pushed hard on climbs.  I’d like to think it was simply that I put out too many watts, but the reality is with a FTP of around 3.8 w/kg… I wasn’t producing super-human power levels, and a Google search showed others had had similar problems with these hubs. When I had the wheels rebuilt later after my accident, Wheelbuilder replaced some of the alloy axle with steel, and the problem was solved.

Recently I’ve decided to try a couple of other different style power meters… a set of PowerTap P1 pedals and a Stages single side crank arm power meter.  Here’s the pro’s and cons for each type of power meter, based on my experience:

PowerTap Hub – Pros & Cons:

  • Pro – Moving from bike to bike is as simple as swapping out the rear wheel.
  • Pro – The technology has been around for many years, and the reliability / repeatability of the design is high.  Other than the problem above, I have had no other problems with the 4 PT hubs I own.
  • Con – They are not easy to swap between wheels, so you either need to choose to put them on your racing wheels or training wheels, or buy two power meters.
  • Con – Unless you buy a wheelset with the wheel, it will cost you to have the PM installed in your wheelset.  Typically this involves new spokes (due to different hub sizing), which can be quite pricey if you buy spokes like Sapim cx-Ray.
  • Con – Switching from 10 speed to 11 speed cassettes require a new updated hub.  For older models with a 12mm axle, PowerTap does not (currently) provide a replacement option, but I found an aftermarket version that worked for my unit here.

PowerTap P1 Pedals – Pros & Cons:

  • Pro – Moving from bike to bike is as easy if not easier than the PT hub.  Simply swap the pedals and you are ready to go.  Unlike other pedal power meters, the PowerTap P1’s do not require special torque requirements or calibration.
  • Pro – Because they are so easy to install / move, they are GREAT to take when you travel and borrow or rent bikes.
  • Pro – They measure each leg independently, so you can see (and hopefully improve) your left / right leg power balance.  With some software platforms, you can also get feedback on pedaling efficiency, for each leg.
  • Pro – They are great for using as a comparison tool.  Besides the comparisons shown for this article, I’ve also used them as test basis for checking the accuracy of power meters from people I coach.  Simply put them on the bike and you can compare to hub based PM’s, spider, crank or even options like my Wahoo Kickr.
  • Con – They are expensive… no getting around it.
  • Con – Subjectively looking at the data, they are more prone to data spikes than hub based systems (slightly higher NP values).  My guess is they are probably more accurately reflecting the actual stress put on my legs… but it’s just slightly higher than I see with hubs.
  • Con – You are stuck with Garmin’s proprietary cleat design and there’s no option for things like standard SPD pedals for mountain bikes (although I’ve used my road shoes with these pedals on my gravel bike and my mountain bike).

Stages – Single leg PM – Pros & Cons.

  • Pro – Initial installation was easy.  Simply remove the existing left crank arm and replace with the crank arm from Stages.  It could be moved bike to bike, but it would be more time consuming that swapping a wheel or pedals (at least for me).
  • Pro – Doesn’t require a special pedal / cleat system, and can work with any wheel… race or training wheels can be swapped out with no changes required with your power meter.
  • Con – Single side power reading may be a problem if you have a leg imbalance, resulting in some lack of accuracy or reliability.

Naturally I wanted to see how these PM’s compared to each other.  Although not the detail providing in one of DC Rainmaker’s write ups, I simply wanted to have a practical understanding about the differences between pedals, hub and a single leg power meter.  I chose a course with a lot of short hills and turns to help drive up the potential for power spikes, to see how the PM’s would compare.  I then broke the ride (about 29 miles each way) into a series of 8 segments so I could compare the power meters at varying points along the ride.  The comparison between the PowerTap P1’s and the Stages single-leg power meter was:

PowerTap P1 vs Stages

PowerTap P1 vs Stages… very little difference in readings, well within the level of accuracy between both units.

The comparison between the PowerTap P1’s and the PowerTap hub is:

PowerTap P1 vs PowerTap Hub

PowerTap P1 vs PowerTap Hub – More difference in this comparison, but the primary difference is due to drive loss causing the P1’s to read higher power numbers.  This has been consistent in every hub I’ve tested.

Note that the two tests were two different days, so the power per segment from test 1 and test two were different depending on how hard I was pushing on that particular day.  Of course the power meters being compared were recorded simultaneously, with two different Garmin units, and each PM was calibrated (zero offset) before the ride, and around 20 minutes into the ride before starting the segments.

The results were very close, well within the tolerances of each power meter.  The only substantial difference was between the hub and the pedals, which was basically due to the difference in drive losses (chain, cassette, etc.). Deducting the drive losses, the power meters would have been extremely close as well.

In the end, there is so much testing and emphasis on power meter accuracy these days, that I think most of the major (and seasoned) power meters will have sufficient accuracy and repeatability for the typical user.

So… here’s my thoughts, based on owning these three styles of power meters:

  • My favorite all around design is the pedal based PowerTap P1.  I like that they are so easily swappable between bikes, easy to travel with and provide additional metrics. Hopefully this design will continue to drop in price… or even better if something like the Limits power meter is actually built and shipped (I have an order in for one of these). As an alternative, I have two athletes that I coach with the Garmin 2S single leg power meter, which is considerably less expensive and still provides portability… but the PM seems a bit more finicky than the Garmin product.
Yes... that's PowerTap P1 pedals and a Garmin 520 on a bike borrowed from my father-in-law in Florida. You can never get too much data...

Yes… that’s PowerTap P1 pedals and a Garmin 520 on a bike borrowed from my father-in-law in Florida. You can never get too much data…

 

  • I’ve been really impressed with the Stages power meter so far.  I have it on my gravel bike, so it is seeing some pretty rough roads and has had no issues. Likewise I’ve been really pleased with the accuracy relative to my other power meters  Based on my experience, I’d have no problem recommending this unit / style, and personally don’t see an issue with single side power meters for most people.  One alternative of Stages is the 4iiii Precision Power meter, which can be installed on your crank arm for $399. This is of course assuming your crank arm and bike frame are compatible.  I actually ordered one of these units for a bike I was in the process building (Trek Domane), and had to cancel the order as I couldn’t provide a picture to 4iiii’s demonstrating there was enough room for the PM (didn’t have the frame when I tried to order the PM).
Stages on my gravel bike.

Stages on my gravel bike.

 

  • PowerTap hub.  I still like this style, but it does have a drawback of being mounted to a single wheel.  This is fine if you only use one rear wheel, but if you use different wheel sets, it’s better to consider other options.  I own both the newer G3 hubs as well as the other style hubs.  The G3 hubs are lighter, but functionally, they perform very similarly (the zero offset reporting is slightly different).

For more on power meters and the in depth reviews, DC Rainmaker provides fantastic overviews here.

 

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