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The Power2Max is one of the newest crank-based power meters on the market today. Its price point is a bit lower than most other crank-based power meters, though, in the same range as rear-hub based power meters. Since the updated second generation Power2Max units became available back in September – I think the game has shifted a bit and they now offer a more competitive product than they previously did – hence my interest in reviewing it.
Power2Max sent out a unit back in early summer for me to check out and evaluate. Since then, I’ve been using it constantly. In doing so, I’ve got a pretty good grasp on how the unit works and all the inside and out details. Because I want to be transparent about my reviews, as I mentioned above Power2Max sent me the unit as a trial unit. Once that period has elapsed, I will send the whole kit back to them (it’s actually already off the bike!). Simple as that. Sorta like hiking in wilderness trails – leave only footprints. If you find my review useful, you can use any of the Amazon or Clever Training links from this page to help support future reviews.
Lastly, at the end of the day keep in mind I’m just like any other regular triathlete out there. I write these reviews because I’m inherently a curious person with a technology background (my day job), and thus I try and be as complete as I can. But, if I’ve missed something or if you spot something that doesn’t quite jive – just let me know and I’ll be happy to get it all sorted out. Also, because the technology world constantly changes, I try and go back and update these reviews as new features and functionality are added – or if bugs are fixed.
Assuming you purchased the Power2Max as just the power meter itself (without cranks), then it’ll come in a rather small box. Sorta the size of a double-CD case (remember those?).
Inside on top is the user manual:
Below that you’ll find an official calibration certificate of the unit, listing the BCD type, serial number, born-on date and slope – along with the torque specifications for attaching your unit. Do follow these torque values. The below certificate is for the older unit (I did unboxing pics for that), but the new certificate is identical.
Next you’ll see the battery hanging out below it, along with a couple extra screws. Put these in a safe place. They are extras, but I assure you in time you’ll manage to lose them off the battery cover. I lost one, somewhere, while changing the battery one day. They are incredibly small and are easy to just disappear (especially with the unit mounted to your bike).
Ok, finally, the unit itself:
As you can see, we’ll have to add the chainrings and cranks – but we’ll do that in a minute.
That triangle shaped pod is the battery and electronics compartment,you can see the three screws holding it on. Those are the same three screws that they provide two extra screws for. So it’s like baseball and strikes as far as losing screws go. Three strike and you’re out.
Here’s the back of the unit:
Now, in the event that they shipped the unit to you pre-installed with cranks, here’s what it’ll look like:
Since it doesn’t have chainrings on, we’ll still have to take off the non-drive side crank arm, as well as as take off the battery cover to plop the chainrings on.
For everyone else, let’s get this puppy all put together and installed.
When it comes to installation of power meters, I’d put this in the middle range as far as complexity goes. At the easiest end is the PowerTap (already in a wheel), and at the not-so-easy end is the Ergomo. This is roughly half-way. Neither easy nor difficult for the average consumer. It’s made easier however if your bottom bracket is already the correct type. And obviously, harder if you have to swap that out. If you’re already confused in the last few lines, I’d suggest bringing a 6-pack to your local bike mechanic and calling it a night.
That said, over the past 6-7 months I’ve gotten really darn good at installing this thing repeatedly. I can do it in about 10 minutes from a power meter of a different bottom bracket type, all the way to this (including swapping chainrings). But for most folks I don’t expect quite that level of efficiency on the first go.
First up is getting the chainrings on the unit. that’s the simple part. You’ll simply grab a hex wrench and attach the two rings (small and big) and then use the five bolts to attach:
If they sent you the cranks already on it, but without chainrings, then you can just remove the battery cover and ‘snap’ the larger chainring on it without having to remove the crank (like above).
Alternatively, you could connect the spider to the crankarm (drive-side) first. Depending on which crank arms you have, this may require a special tool. In my case, they sent me ROTOR cranks to utilize, which meant a special adapter. And then a vise to tighten the whole thing:
Be warned, if you ever have to remove the drive-side crank-arm, it can be a solid PITA depending on how tight the person attached it. Trust me.
Ok, with things largely in one piece, let’s get it on the bike (I’m going to assume you’ve sorted out any bottom bracket issues, just ensure you’ve got the right bottom bracket on there):
Once it’s in there (and your chain is in there, don’t forget!), then you’ll go ahead and attach the non-driveside crank arm.
If you have a ROTOR crank as I did, be aware that the tightening bolt is a bit funky. You’ll first use a wrench to tighten the cap in place (in the photo above, the hole that would extend into the bottom bracket), and then you’ll tighten the small bolt on the side (in the photo above, the small bolt you see at the right edge of the crank arm, facing up). Note that the small bolt is not meant to come out. If you try, it’ll crack. It makes for a bad day.
In general, once you’ve got everything set, I highly recommend doing a couple of trainer rides before you head outdoors. That’s my general mantra anytime I work on my own bike (I have more trust in a bike mechanic than myself).
I figure if something is going to go wrong in that area of my bike, I’d much rather it be in front of my TV, than descending at 30MPH.
The Power2Max utilizes a Renata 2450CN coin cell user-replaceable battery. Note, I specifically called out the brand here – Renata, as I’m told that other 2450CN batteries are actually not compatible. So if you buy a small stock of batteries to have around the house, then you’ll want to ensure you get the right brand.
In general, I recommend that you get a few batteries and stash one in your car or bike bag, just to have there. Much easier to buy them now, rather than when you get the low-battery condition.
In any case, the battery pod is accessed via the three screws we discussed earlier. It has two o-rings to keep it weatherproofed. Interestingly, if you look carefully at that little white label, the ‘SN’ is actually the ANT+ ID – making it easy in the event you need to know your ANTID for pairing purposes (normally, you can just search, but if you were in a group setting and forgot to pair in advance then there ya go).
The battery lasts 300-400 hours of active cycling time. The unit will automatically shutoff after a couple minutes of inactivity (any movement). To wake it up, simply move the crank arm and the accellerometer will turn on the unit and start broadcasting.
Day to day use (with ANT+ head units):
This section will be short, since I cover much of it elsewhere in this review, and in the various head unit reviews.
The Power2Max uses ANT+, and thus, an ANT+ head unit is required. The major choices come from Garmin, Timex, CycleOps (Saris), O-Synce and a handful of others. On the phone front, you can use some Android phones that includes ANT+, as well as an iPhone with the Wahoo Fitness ANT+ adapter.
When it comes to pairing, most power meter head units operate the same way. For the photos below, I’m using an Edge 510 – but again, most are roughly the same. You’ll be going into your bike profile, which is where the ANT+ accessories are typically stored on bike computers. Within that section, you’ll be enabling the power meter sensor:
After which, you’ll commence a search for nearby ANT+ power meters. You only need to do this once, and it’ll remember the data for any future rides. Just be sure to do this with no other bikes with power meters around you. In other words, a group ride is not the time to do an initial pairing.
Once that’s completed, you’ll want to complete an initial manual calibration, per the next section.
The Power2Max supports a few different calibration and accuracy related options and features. One of these is new to models produced after September 2012 (temperature correction). But the rest are common across all Power2Max units.
First, it supports auto zero. Auto zero means the unit is automatically calibrating itself at specified points in time. In the case of the Power2Max, this is anytime you stop pedaling for two seconds. There is no end-user notification that this has (or hasn’t) occurred however, nor can you turn it off. Functionally, this is no different than pressing the ‘calibrate’ button.
This is unlike most power meters, as the power meter unit doesn’t allow you to turn this on or off. For example, compare below a photo (first) of the PowerTap, and then secondly of the Power2Max configuration screens. Note the lack of Auto Zero option on the second photo (Power2Max):
In addition to auto-zero, you can also manually calibrate the unit at any time by going into the settings on your bike computer (they’ll all differ slightly), and press calibrate. Note that you need to have stopped pedaling to do so. If you’re pedaling, then the unit will produce an error.
Assuming the calibration is successful, it’ll spit back a value at you – though there’s admittedly not much you can do here, since you can’t otherwise take this number and do anything with it other than monitor it:
Next you can do a static torque test – though the Power2Max folks would prefer you not do so. Steve Irwin has written up the most clear instructions for doing so on his post about the first generation of the Power2Max unit. A static torque test involves using a known weight source and then some math afterwards to validate the numbers being given. For 99% of users, it’s not something you’re going to venture into. Here’s what they (Power2Max) noted in an e-mail to me:
“We don’t recommend a static weight calibration test. Dynamic calibration (i.e. with the crank turning) is more precise than static calibration. We calibrate our power meters dynamically and recommend, if people want to verify the calibration, to check the values against those they get from a Cyclus 2 ergometer (it also has an accuracy of ±2%).”
Finally, one new feature in the second generation Power2Max units (those made after September 2012) is temperature correction. This is quite frankly the singular reason why the Power2Max went from being ‘so-so’ to ‘perfectly fine’. Prior to this, many users would see ‘drift’ of numbers over the course of a given ride due to shifts in temperature (in many cases upwards of 40 watts!). For example, starting at 8AM the temperature might be 45*F, and then at 12PM it could be 65*F. Within that timeframe as the temperature rose, the strain gauges were being impacted by the temperature change but not updated accordingly.
Based on what I’ve seen, along with what many others have seen over the last few months – this change seems to have resolved these issues.
Cadence is how quickly the crank arm is rotating, typically displayed in Revolutions Per Minute (RPM). In general, most people tend to have cadences in the 80-95RPM range. There’s a whole religious battle around cadence and where the most appropriate place to be (or not to be) is. I won’t get into that. That’s all training stuff and nothing to do with the product. Instead, I’ll simply note how it works here in relation to the Power2Max.
Unlike most crank-based power meters on the market today the Power2Max does not require a cadence magnet. Instead, the unit includes an accelerometer to automatically determine your cadence. In doing so, it’ll then transmit that cadence information to your head unit, which will display it in the appropriate data fields (typically cadence). As well as record it for later reference:
The Power2Max has a range of 30RPM to 200RPM. And while I never had good reason to go down to 30RPM, I have tested it as high as 190RPM without issue. Looking through my files, here’s one data point I was able to find showing it in the mid-160’s during a workout:
As one who does a LOT of cadence related drills, I can say that the cadence here appears pretty spot-on with a standard cadence magnet setup (either in a power meter or in a separate sensor). There’s a tiny bit of a delay compared to a standard cadence magnet, but not terribly noticeable if you didn’t otherwise know.
Left/Right Estimated Power:
In addition to the temperature compensation, the Power2Max second generation units have introduced power balance information.
The goal of power balance is to emulate Left/Right power (as in, from your left leg and right leg). The unit does this by measuring the power output of the stroke across two sections (both on the right side however). The first half of the stroke is measured from 12PM to 6PM (as if looking at the crank from the side with the chain rings), and the second half of the stroke is measured from 6PM to 12AM. Normally this is referred to as the down stroke and upstroke. For most cyclists, they will exert the vast majority of their power output during the down stroke (first half), while pressing down. During the second half of the stroke, the left leg would then be on the down stroke (since pedals are oppositely arranged/connected). Thus, the Powr2Max makes the assumption that power outputted during the second half of the stroke is actually coming from the left leg.
To help illustrate this a bit, I’ve taken the crank and divided it up into the two sections. When the pedal is within the first section (down stroke), it’ll report the power exerted as right-driven. While in the second section (up stroke), it’ll report the power as left-driven.
The indirect left/right power measurement and estimation is most noticeable in a simple one-legged drill. In this case, I would alternate between my left leg and right leg for 30 seconds at a time, whereby I would entirely remove my non-primary cleat from the pedals entirely (meaning I unclipped and let it rest on the back of the trainer). You can see that despite being fully on a single leg, the Power2Max will report that I’m closer to about 80-90% of one leg, rather than 100%. Whereas as a pedal-based power meter will report 100% or 0%.
If I really focused on the upstroke, I could actually increase the right power even further (incorrectly). Conversely, if I attempted to remove all of the upstroke, then it would get much closer to zero. However, that would somewhat defeat the point of the drill (and make it more difficult to pedal). But, the general point here shows that it’s not a foolproof system.
Which, gets to the deciding on the exact value of power balance. Like even true Left/Right power (such as on the Polar/Look Keo system), there exists very little guidance on what or how it’s best used in a specific training setting. There exists many thoughts on how some of the specific pedal based power meters could be used by changing cleat position to increase power output, but very little is out there today on how to truly use left/right power data. In many ways, it’s being looked at like cadence – that ultimately self-selected cadence may be the most appropriate option for most riders.
I do think that over time, there will be better research in how exactly to use left/right power data to increase cycling fitness, but even once those recommendations are made – the ‘estimation’ factor of the current Power2Max implementation would likely mean that they wouldn’t be realistic to utilize it in a left/right setting due to the lack of accuracy in the estimation method (assumption of no residual power). In fact, even Power2Max themselves says there’s little value in it other than from a marketing standpoint (quote at Eurobikethis year).
That all said, here’s how the data shows up on the head unit. First, the Power2Max actually doesn’t transmit true left/right information directly to your head unit. Instead, it transmits total power, and right % of power – per the established standards on how to transmit power balance information. Then, the head unit (according to ANT+ specifications) will go ahead and determine the left power percentage and wattage. Simple grade school math for the most part.
Once that’s done, you’ll see it display on your head unit. Today, supported units includes the Garmin Edge 500/510/800/810, Garmin Forerunner 910XT, and the Joule GPS.
Below, you can see me having Lap Balance configured, as well as Average Balance.
Outside you can see the same thing, along with a rare occasion where my balance was spot-on. Very rare. It is relatively easy to shift your balance and get them to line up – but again, there’s just little value in doing so.
When it comes time to display the data on sites, different platforms show it differently. For the sake of keeping this simple, I’m just going to use Garmin Connect. Below, you can see my power balance data as displayed on the chart. You can see that according to this particular ride, I was more right-leg heavy than left-leg.
This same information is displayed along the left side as well. For example, you can see the Left/Right balance shown at 47/53%.
As I said before, balance information is an interesting bit of trivia, but it’s not super-useful except for scenarios of recovering from an injury in one leg and the distortion between the legs is so vast that it becomes immediately clear in the balance information.
I often note that there are few things I despise more than doing in-depth power meter accuracy tests. Primarily because it’s excruciatingly difficult to do correctly (especially in a non-lab environment), and because nobody is ever happy with how you executed the test. The reason being that you have to correlate multiple power meter files from multiple head units, and hope that all head units operated properly every time. No skips, jumps, crashes, or other funkiness.
For example – are all units installed correctly? Are all units calibrated (correctly) at the start of the ride? Are they re-calibrated and/or zero offset updated at some point after the unit warms up? Are they all started at exactly the same time? Same recording rates? Do any units auto-pause (like the Joule) once started? If you stop mid-ride, are they all stopped at the same time? How is change in weather or temperature affecting it?
Hence you can see why virtually everyone that does detailed power meter comparison tests does so indoors and in a lab environment where the rider is typically given a set timeframe to ride and all devices can be monitored by a 3rd party concurrently.
That said, I’ve done some basic comparisons. I’ve had the Power2Max on my bike since earlier this summer, and then swapped it again a few months ago with the new unit. All of the data you see here is using the new Power2Max unit with the temperature compensation.
These tests each compare it against other power meters or trainers, both inside and out. I don’t however make any claim that one is more accurate than other because quite frankly there’s no way I could know that. In general, I’m simply noting that the data ‘is what it is’. Make sense?
As a general rule, all units are manually calibrated at the start of the the ride, and then typically again about 10 minutes into the ride. From there, I let each units internal technologies deal with correction/compensation. Note that I am working with some folks to standardize these tests going forward, likely for reviews starting in February.
1) Indoor Trainer:
Units compared: Power2Max, PowerTap G3, Kinetic inRide Trainer
This was a pretty standard slightly less than one hour trainer ride. It included a variety of drills and different segments from low cadence to high cadence.
Here are a few of the different segments of the workout:
As you can see, all three units tracked incredibly closely. There was very little variation, with the low-cadence work being the one area we saw a tiny bit more variant than normal – but still within 2.7% of each other – or less than the difference between the two units when it comes to claimed accuracy (overlapping).
2) Outdoor Ride:
Units Compared: Power2Max and PowerTap G3
This ride was more in line with a standard ride for me outdoors. It started out just before dawn and then lasted until after sunrise. It’s interesting in that the temperature changed a bit during the ride – which makes the data more relevant to the Power2Max temperature compensation aspects.
Here’s the power graphs, with a 10-second smoothing to make them easier to read:
Zooming into it a bit, you can see they track pretty closely. Though, it’s admittedly a bit hard to see given the spikes (even with 3s averaging in the graphs below):
For fun, I’ve picked out two 5 minute chunks at random. I decided on the 15-20 minute marker, and then the 50-55 minute marker, and just wanted to see what the average power looked like for those sections. I thought this might be an interesting indicator to see if any drift was occurring over the course of the ride:
Now, there does appear to be some difference there – especially in the first section. However, keep in mind that that first section had a number of stops/starts in it, which may represent slightly different handling of quick changes in power.
For the entire ride, the data looks like:
Full Ride Averages and Max’s: PowerTap Average: 192.9w Power2Max Average: 186.9w Average Variance: 3.2% PowerTap Max: 514.3w Power2Max Max: 484.0w
As you’ll note, the PowerTap is reading slightly higher than the Power2Max (normally it would be the other way around). However, at 192.9w, +/- 1.5% would mean on the low end 190w, and the Power2Max at +/- 2% would mean on the high end 190.5w. In other words, they are both within the margin of error of being pretty darn close. No way of knowing who is more correct.
Power Meter Market Comparison Chart:
Here’s a comparison chart of units on the market today that I have reviewed or otherwise ridden. Note that I don’t include units that I haven’t used in there, since it seems silly to include ones that I can’t provide direct feedback on.
I do however (based on popular requests for other products) include units that are pending shortly, in those cases, I’ve put a TBA/TBD in the data fields as appropriate. Note that the below chart is updated dynamically in real-time from a database, with the most recent update listed at the bottom. If products are updated (such as a firmware release), you’ll see the table update.
Finally, you can click to expand the table and get a whole lot more info. It’s just a page size limitation thing. All good? Good.
Again, remember you can expand the table to see more info, and then mix and match the power meters as you see fit. Or you can do the same over at the product comparison tool.
The reality is that power meter selection is a highly religious thing for many. If you visit this post in a few days/weeks/months, – you’ll likely see that in the comments. Everyone who buys their power meter swears by it – and believes it can do no wrong. This is true whether they spend well over $2-3K for an SRM, or a couple hundred dollars for a iBike. There’s nothing wrong with believing your purchase was the correct one.
The challenge is that people from both extremes attempt to make product purchasing decisions about individuals other than themselves. The reality is that people purchase things at different price points for different reasons. Some will spend $2-3K for a power meter because it fits their use case perfectly, while others are fine with compromises by saving $1-2K. There are tradeoffs, and the fact is that some of those tradeoffs are accuracy, and some of those tradeoffs involve money. And some involve configuration options. It’s up to you to decide what’s most important…to you.
I found for my training over the last 6-7 months, the Power2Max was sufficient for my needs. I was able to both train and race based on it, and had no problems doing either. At the end of the day, that’s pretty much where I sit when it comes to power meters. Can the unit produce data that I (me) can train by, and can I then execute on that data in a race situation? Further, is the unit easy to use on a day to day basis, and does it offer a hassle-free experience? In both cases, I can say it does (for me).
From a functionality standpoint, the temperature compensation in the new units is critical. I probably wouldn’t buy an older used Power2Max due to it (primarily from the standpoint of historical data potentially being skewed). Though, as I note below you could buy an older unit and upgrade it. The newer Power2Max units all have it in place today (and at the same price as the older units). I don’t find any real training or racing value in the left/right metrics (especially being estimates), so I wouldn’t personally choose this unit over others because of that functionality. As I noted above, there is very little that a lot of smart folks in the power meter world have been able to do with those metrics to date.
One minor note, Power2Max has announced they they offer upgrades for existing owners for $50US/€50. This includes both the left/right power additions as well as the temperature compensation. If for some reason you just want left/right power, that’s $10US/€10. Note that you will have to send it in to your respect distributor (wherever you bought it from).
Pros and Cons:
Here’s a quick table of the pros and cons of the Power2Max Power Meter.
– ‘It just works’ factor – Accurate power measurement – Temperature Compensation in second generation units – Relatively straight forward installation – Cadence without a cadence magnet – Contains have left/right estimated power (though value is questionable) – Do not have to send back in if changing chainrings
– No method to turn off Auto Zero – Tiny delay in cadence readings
Thanks for reading! And as always, feel free to post comments or questions in the comments section below, I’ll be happy to try and answer them as quickly as possible. And lastly, if you felt this review was useful – I always appreciate feedback in the comments below. Thanks!
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