PowerTap PowerCal Review – The Ultimate Zwift Starter Tool

PowerTap’s heart-rate power meter is a novel invention that brings live power data to any ride at a fraction of the price of a traditional power meter. And, best of all, it’s an instant, accessible way to get on Zwift, no matter whatever other equipment you’re using.

Power Data Derived From Your Heart Rate

The PowerTap PowerCal (formerly branded the CycleOps PowerCal and released way back in 2013), is unique in the power meter world. There are smart heart rate monitors that add analysis to a device that ordinarily just records or relays your data, and there are currently tens of companies rushing through affordable power meters, many of which are based on smart interpretation of other conditions rather than direct power analysis. (And it’s not just startups, see the Garmin Vector Air rumors, for example.) But to date, the PowerCal is the only device that combines the smart HRM and interpretive power worlds.

The PowerCal works by interpreting your heart rate data and determining your power based off an internal algorithm. This doesn’t just mean that a higher heart rate is reported as a bigger power output—it looks at changes in your heart rate and other patterns to give you a live power reading that’s surprisingly accurate (I’ll get to that later). It’s a power meter that works with every bike you own. And it’s $40.

Easy, universal Zwift access is the device’s main value proposition, and it’s a good one. There’s no beating around the bush: Zwift is the perfect use case for this device. So much so that it’s almost hard to believe the PowerCal existed before Zwift was a thing.

Zwift

The PowerCal works with Zwift. It’s actually astounding how easy it is to get into Zwift using this device. If you’ve got an old bike and a turbo trainer to put it on (or even an old exercise bike covered in clothes), all you need is the PowerCal to get started. Pair the PowerCal to your computer or companion app, and start pedaling. That’s really all there is to it.

I’ve ridden Zwift events on a gifted bike and a $20 trainer, using the PowerCal to turn my garbage equipment into smart trainer (ok, kinda). Zwift’s been around for so long and is so popular, the only possible reasons you could’ve avoided it are because of the high-priced barriers to entry (smart trainer and/or power meter) or difficulty in understanding what gear you need. That’s what makes the PowerCal so useful. The PowerCal is the easiest, cheapest way to get on the Zwift platform, and while it’s not a perfect experience, it’s certainly good enough.

And in fact, it has its uses beyond just an entry level intro to Zwift. As somebody who’s lived on the road traveling with various cycling brands, the ability to Zwift from a hotel gym, for example, is a game-changer, and a hell of a lot more valuable than trying to translate garbage gym bike spinning programs back into something your training plan can understand.

Zwift is where this device comes into its own. In fact, I’d wager that a huge percentage of PowerCal sales over the past 24 months or so have been made specifically with Zwift in mind.

OK, But How Well Does It Actually Work With Zwift?

Pretty well! It pairs quickly and it feels right when you ride. There’s a discernible lag when you start pedaling and when your effort changes, but it’s fairly tolerable depending on the kind of riding you do.

For spending 45 minutes cruising Watopia on an evening, it’s pretty satisfying. You pedal, your avatar moves. Once you’re rolling on a solo ride it’s an enjoyable experience, and there’s a lot of fun to be had just getting an evening ride under your belt.

For group rides like gran fondos, it works ok. It can be hard to sit with a group because there’s an input lag (more technically, it’s because the PowerCal measures something that happens after your power output changes). But actually, it works fine too.

Aside: My first Zwift grand fondo ever, back when I was very fit and being paid to represent brands at real gran fondos, I used the PowerCal and finished in fourth place. I yo-yoed on the final mountain climb, trying to pull off from the pace-setting only for the lag to drop me out of the group, then finding my efforts to regroup would push me off the front again. Close to the finish, a guy jumped out of our chasing group of four and I had to watch as he rode to second place while my avatar took his time to react to my effort in response. It wasn’t a bad experience by any means, but the PowerCal’s limitations were exposed. In gran fondos that I’ve taken less seriously, like the Tour de Zwift, I’ve actually really enjoyed using it (especially since it means I can ride with a beater bike or fixie for some more fun).

For racing… well, I haven’t been brave enough to even try it. In fact, since the PowerCal now displays as zPower rather than a true power meter, you might be hard-pressed to find an interesting race to ride anyway.

For training, forget it. The delay in getting your power up or down into the right zone is slow enough that you can miss entire intervals on Zwift. You’ll just have no idea if you’re really hitting your targets.

Accuracy

Zwift might be the first use-case that comes to mind, but everybody’s first question is whether the PowerCal is accurate. The short answer is yes. Kind of. That is to say that the power output you’ll see is more or less the power output you’d expect, and more or less in line with a more traditional (and costlier) power meter. However, it’s much worse at the lowest and highest effort ranges, and it’s slow to respond to change—both factors that severely limit, but don’t entirely diminish, its value as a training device.

What you’ll probably find is that the PowerCal comes up about in line with power estimates from other services. What it really has over those services is that you can see the power in real-time rather than after the fact. And again, it’s about right (where the benchmark for “right” is a more expensive power meter). Still, it’s hard to vouch for the accuracy of any device claiming to be a power meter when you can stop pedaling and still see your data rising.

Because it’s not a true power meter—and I really do use that in its loosest term, since it does measure power quite accurately—there are idiosyncrasies you can take advantage of. You can achieve huge power outputs through gaming the device’s measurement methodology, temporarily soft-pedaling before a big effort to see big power numbers. That’s great if you want to overlay your data on a video, Instagram influencers. Again, it all averages out, and so I haven’t found any real value to gaming the power this way in Zwift. Still, it shows a little more of the calculations behind the scenes than I’d really like from a device that’s supposed to be tracking my data accurately.

DC Rainmaker and Titanium Geek both have their own data on how accurate the PowerCal is. Big picture: we all think it’s just about accurate enough. Just about.

The Tech

The PowerCal looks like a regular heart rate monitor. It uses the same connections and strap you’re used to, and it’s no bulkier than other heart rate monitors on the market. Next to the 4iiii Viiiiva, another heart rate monitor that does something quite interesting, it’s hard to tell them apart beyond the graphics printed on them.

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It works by measuring your heart rate and the fluctuations caused by exercise to estimate a power output. Given that the algorithm is the only thing setting this device apart from every other heart rate monitor on the market, it’s no surprise that it’s fairly well guarded, though I will add that enthusiasts have come close enough to cracking it with their own calibration programs.

Calibration is, however, entirely unnecessary. The rumor goes that Cycleops intended to gather rider data as part of an initial configuration, but found that their algorithm put out consistently accurate data by default. I’m guessing that it could be personalized to give marginally more accurate results, but the nature of the device means you’re only ever really looking for a “good enough” result anyway.

It’s powered by a watch battery that’ll last for a year of use, more or less. There are some reports of PowerCals arriving with weak or near empty batteries and giving erratic results, but with a fresh battery it’ll just work reliably for an awful long time.

And it probably goes without saying, but it also shares your heart rate data with whatever you’ve paired it to. You’ll get both heart rate and power from the one device, simultaneously.

On the road

Although it’s perfect for Zwift, the PowerCal was built for the road originally. It’s easy to see why it didn’t really take off that time around, since the use-case for power on the road is much more niche and focused on reliable data.

As mentioned earlier, the data you see out on the road won’t be drastically different from Strava’s power meter estimates. There’s certainly value in retroactive analysis of your PowerCal data, but the core value proposition over just trusting Strava’s estimate is the live data you’ll get out on the road.

It’s a live estimation of your power that’s more than accurate enough to be useful. You can’t really train with it, but it works for converting your heart rate into a more useful data point, and quantifying your effort.

On Zwift, where power and FTP are your main focus, its weakness are a little more visible. But when you’re out riding, not always looking down, it actually works well. The power it reports usually feels right when you glance down at your head unit. This is at least true for even, sustained efforts. There’s perhaps an argument that if you’re just sitting at a constant effort every ride, maybe you don’t need a power meter at all. Maybe. I do love this device, but I’ll reluctantly concede that it has a limited use-case if you’re buying for only for use on the road.

Where it really has value is that it adds power data to any bike you own. Winter bike, track bike, mountain bike… whatever. Wear the PowerCal and you get power data for your ride. I’ve even had fun riding my fixie to the bar and checking my data later. (It’s a bit awkward turning up to a bar and removing a heart rate strap, but it’s kind of expected of me at this point.)

For training

The internal smoothing and frustrating lag makes intervals pointless. You’ll spend your time watching the numbers very slowly rise or fall to where you need them (and sometimes they just don’t get there at all).

It does give you reasonably accurate data for analysis. You can ride at, say, 75% FTP for two hours. But it’s just not enough of a training tool. Not really.

Sorry. This is why people weren’t buying it until the Zwift phenomenon blew up.

Compatibility

There are a few versions of the PowerCal, supporting either/or ANT+ and Bluetooth. The version I tested only supported Bluetooth and it connected with everything I threw at it with no problem (with the usual exception of the Hammerhead Karoo, which refuses to behave normally as policy).

This level of compatibility really is quite the surprise. While multi-use sensors are increasingly popular, the “heart rate and power” combination is unique. You’d forgive head unit manufacturers for being confused by it, but your Garmin will see the PowerCal as a power meter with no problem at all.

It even works with the Strava app, or at least it did until recently.

Conclusion

The PowerCal won’t replace your power meter. You won’t downsize for it if you’re running something more serious. It’s a great toy though, and a good enough entry-level tool for somebody looking to start experimenting with power data. And it’s absolutely perfect for Zwift, either as a starter kit or a backup that lets you Zwift from anywhere using any equipment.

It’s not the best option for live power nor for Zwift. But it’s also not a terrible choice for either. It’s accurate enough and versatile enough that it’s a fun, useful tool for anybody’s repertoire.

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SRAM acquired PowerTap in May 2019. PowerTap’s power meters are now under Quarq branding, and the PowerCal is no longer produced.

Update 12.26.2019: The PowerTap PowerCal does not work with RGT Cycling. It displays only Heart Rate and not power.