PowerTap C1 Power Meter Review – Zwift Gear Tests!

PowerTap is one of the original names in the power meter fields. With the explosion of power meters from various companies in the last few years, the PowerTap C1 power meter mounted on the chainring and pitched at a very attractive price point is a very clear challenge to the new bloods. Is the C1 worthy of the PowerTap name?

PowerTap C1 Power Meter Review – Chainring mounted watts!

PowerTap C1

Today is the start of my series of “Zwift Gear tests”. The PowerTap C1 is a good example of a product which should give a useful Zwift Gear test. This power meter has been out on the market for a while, thus I’m unlikely to bring anything new to the table in term of it being a cycling power meter. However, the focus on these reviews will be looking at how a product functions specifically when used for Zwifting. Hopefully, this will give people an idea of kit which might be useful for building their Zwift Caves – so without more ado:

The PowerTap name is well known. As the number of power meters has grown, manufacturers have tried to identify different parts of the bike where power meters can reasonably be attached.

We now have power meters from pedals, all the way through to the hub on the rear wheel, but most options are focused towards the front end of the bike, placing power meters on the crank arms, and the spiders.

Building on existing knowledge within the company, PowerTap decided to target a so far unused location, the physical chain ring

Device Design

I’m was a little surprised when the PowerTap C1 came through the door. Enclosed in a jiffy bag, it really does strike you as a slim package

PowerTap C1

When you order the PowerTap C1 you have a choice of teeth numbers on the rings, and on that initial selection you can also see the cost to replace chainrings giving you an idea as to what you are buying into – small thing, but I do value how open PowerTap are about the costs of replacement parts, as that can factor significantly in a person’s purchase.

PowerTap C1

Inside the box, we’ve obviously got the PowerTap C1 itself.

PowerTap C1

In addition to the power meter, there is the warranty card, manuals, and the five bolts and nuts you’ll need to use to attach the PowerTap chainrings to your spider.

PowerTap C1

Only a small thing, but the FSA branded bolts arrive with thread lock already applied. The chainrings in question are also made by FSA, but I have been unable to find out exactly the model type, or if they are a custom design for PowerTap

PowerTap C1

Finally, there is the actual black box of the power meter, attached to the chainring

PowerTap C1

PowerTap C1

It is at this point the first question mark about the C1 gets raised – why only a 5-bolt pattern? Even in 2016, there has still been no update or release of a 4-bolt pattern PowerTap C1. Just to put that into context, the 4-bolt pattern Shimano Ultegra 6800 was unveiled in 2013, and the Shimano Dura Ace 9000 in 2012! 4-bolt patterns are not exactly brand new concepts today so what is going on?

Using the PowerTap C1

Crank based power meters such as the Stages offering, or pedal located meters like the Garmin Vectors are relatively simple to install. That is not to say the C1 is a difficult installation, but it does require a little more work

First off, removing your old crank set from the bike (Due to the lack of a 4 bolt system, I’ve had to change from using my regular Shimano Ultegra 6800 set, to a 5 bolt 105)

PowerTap C1

Crankset in hand, you then you need to detach your old chainrings. The procedure of both remove and subsequent C1 installation is made a lot easier if you have a torque wrench and gloves to hand

PowerTap C1

Then slotting everything together – whereupon everything, unsurprisingly, lines up very nicely.

PowerTap C1

Bolts and nuts are applied around your old crank, and the C1 rings, with an advisory note in the manual (I know, I hang my head in mock shame, reading a manual!!!) stating they are to be tightened in a star-fashion

PowerTap C1

I’m not astonishingly mechanically minded, but never the less I found the whole installation took me about 10 minutes, the only major irritation was realigning the Ultregra front mech!

PowerTap C1

Once installed to your bike, you’ll need to check for Powertap C1 firmware updates  by installing the PowerTap App to your iPhone (no android love here)

PowerTap C1

The app will immediately alert you to any available updates. A small point I like that PowerTap lists all of the firmware changes when it highlights an update  is available, rather than just demanding  “UPDATE ME!!”

Thinking about the almost budget nature of the C1, if you didn’t have a cycling head unit, the PowerTap app is able to fill in there, allowing you to record your rides outside, using the iPhones internal GPS, and data from the PowerTap C1 using BlueTooth

You can also connect 6 fitness cloud services to the app to export your data to after the ride

PowerTap C1

Compatibility note

Earlier I mentioned the oddity of PowerTap building a new power meter which, at least with regard to Shimano’s catalog, is targeting a previous generation of group sets. Heck, even Shimano’s 105 went to a 4 bolt pattern in early 2015! So this choice looks either rather myopic on the part of PowerTap or gives an indication as to which end of the market the PowerTapC1 is aiming at. Even if PowerTap are targeting the budget conscious individuals who are looking at a £350 group set, I’m not sure they are necessarily going to be inclined to the spend an additional £550 to purchase the PowerTap C1.

I think that is highlighted by looking at the compatibility charts, or more importantly looking at the incompatibility chart – most of the current generation of crank sets, from all manufacturers, are simply out of luck. Certainly, before buying a PowerTap C1, I’d send a good deal of time scrutinizing the compatibility chart here 

PowerTap C1

Specification

  • Crank Interface: 5 bolt, 110 BCD compact (see above for issues with this)
  • Metrics: Total Power, Cadence, power balance (ESTIMATED)
    • Estimated in the sense that the C1 takes the power at the top of the stroke for one leg, and the bottom of the stroke for the other. So very clearly not a true representation as you’d see with the P1 or Vector pedals
    • The C1 can auto zero during the ride to help with accuracy
  • Connectivity: ANT+ and Bluetooth SMART
  • Tooth Options: 50/36, 52-36 and 53/39
  • Added Weight: About 150 grams
  • Battery: CR2032
  • Battery Life: 200 hours… ok

Manual

For those interested in the  PowerTap C1 manual, it can be found here

Using the Device

Talking about power meters, I think it’s reasonable to discuss comparisons with the Garmin Vectors and the Wahoo KICKR I’m familiar with when using Zwift

PowerTap C1

When the Powertap C1 is installed, the manual suggests that there is a break in time of approximately 15-60mins for the power meter, and the screws to settle in. By comparison, both the Stages and Garmin Vectors power meters are good to go after about 30 seconds of settling in, but I suppose in both cases there are fewer screws to deal with!

I found this wasn’t really the end of the world, as it gave me a reason to perform a Zwift FTP test with the Wahoo KICKR used as a power meter, and letting the C1 bed in – it’s also worth while noting when you connect to Zwift, you can see that the PowerTap C1 also is able to record your cadence

PowerTap C1

PowerTap C1

After the break in, the Powertap C1 was ready to be used outside, and connected to your regular head unit for ease of calibration.

When you want to initiate a connection, simply wake the C1 up by giving the crank a spin. The perhaps another spin as well. With the Vectors, they seem to be practically instant on, whilst in comparison, the Powertap C1 sometimes feels like there is the need for a couple of seconds for the unit to come out of its power saving slumber. The fact that there are no external lights on the unit does somewhat add to that “Are you awake” feeling when you are getting set up.

Powertap C1

Similarly, the Powertap C1 really likes to sleep, if you are inactive for a minute or so, it dozes off rapidly in order to conserve battery if it is not being used – something to think about before a Zwift race perhaps if you have to go and fill another water bottle before the start

Having installed the PowerTap C1, and given it a controlled settle in period on Zwift, it seemed a reasonable to use the C1 as my power meter for the Prudential Ride London.

Powertap C1

Over the 100miles, I didn’t see any issues of note. The chainrings produce marginally more noise than my Ultegra rings do, but other than that, a good trial by fire

PowerTap C1

In terms of trial by fire, I can’t say the same for the body riding the bike, though! – Yes, that is my shoe on the handle bars! I was relatively uncomfortable when I passed the finishing line and found it much better to walk down the tarmac in bare feet past the Palace

As I stated, I wasn’t aware of any specific issues with the PowerTap C1 working as a power meter during the ride, and the data seemed entirely reasonable

PowerTap C1

However, one ride, where things “seem to go ok” isn’t really a great test – so onto Zwift and the KICKR, for controlled 5km spin and a few sprints (Both power meters calibrated and a spin down performed on the KICKR before the test)

So given that the KICKR is at the end of the drive train, whereas the PowerTap C1 is directly mounted on the chainrings, a small amount of drive train loss is expected. With zero readings from the C1 accounted for, the average difference between the KICKR and the C1 power reading was 5.9watts. Which is in the ball park for expected drivetrain losses.

Both power meters appear to track nicely, and respond to increases in power without any discernable lag when looking at on overview of the power data trace from the Zwift session – headed towards the mountain

PowerTap C1

If we then concentrate on one of the sprint sections, we can see the Powertap C1 and the Wahoo KICKR still tracking nicely tracking together from the steady pace, through the increases in power. Both meters then regrettably demonstrate the failure of my own legs to be able to maintain my target 400 watts over one minute! So far so goodPowerTap C1

The PowerTap C1 appears to respond to increases in effort marginally before the KICKR does, but that can easily account for by the strain gauge, vs flywheel differences between the two devices. Although it might also be worthwhile considering any difference between Bluetooth (on KICKR) vs ANT+ (C1)

In terms of using the PowerTap C1 on Zwift, it is also crucial to point out that the signal strength of the C1, appears a little weaker than other sensors

PowerTap C1

The dongle hanging off my radiator is 56cm from the furthest point of the PowerTap C1 in a crank rotation I have occasionally noticed a few signal drop outs

PowerTap C1

That might initially be considered “unfair” as we know that Zwift needs to be in close proximity to the sensors due to the volume of data being transmitted. HOWEVER, I haven’t previously had issues with testing other kit with this location – my USB extended cable doesn’t change length between reviews after all! It would also be worthwhile noting that I haven’t noticed any dropouts using a Wahoo Cadence sensor, mounted on the opposite crank, suggesting that the PowerTap C1 may indeed have a weaker signal.

I highlight that the issue may relate to signal strength, as when I was noticing Zwift drop outs, everything was fine with the PowerTap C1 outdoors. A fresh set of batteries seemed to reduce the dropout frequency, but not totally cure it

PowerTap C1

PowerTap C1

Speaking of Battery life…

The reported battery life of the C1 is about 200 hours. Now there is NO WAY that I have spent 200 hours on the bike in the ~ 60 days I’ve been testing the C1, (I wish!) yet as mentioned I have had to change the battery once on the C1 due to signal drop outs. However, I received no notifications that the battery was getting low from either the Powertap app or cycling head unit

The most annoying example of this was simply when the C1 simply appeared to die during a Zwift race at 40km in. PowerTap C1

Thankfully I was also riding on the KICKR at the same time, so was able to relatively easily swap over to using another power meter and continue. However the loss of the draft did mean I lost initially about 20 secs swapping power meters, and then ended up all on my lonesome as the larger group powered away

PowerTap C1

Now batteries fail, that is life. HOWEVER, the PowerTap C1 phone app ideally should have communicated an issue with the battery life well before we arrived at a point where I lost juice mid ride. With the Wahoo Elemnt, the iOS app has a background functionality, so when you finish a ride you get a little note about battery power, and if you need charge things. Perhaps that reflects a different approach to app design and is merely “one of those things”

HOWEVER whilst you could argue that not seeing any alerts on my phone was my issue, and I should also have manually checked the app on my phone occasionally. I also didn’t receive any alerts via any of the other units I have tested the PowerTap C1 with, that being the Wahoo Elemnt, Garmin 1000, or Garmin Fenix3 HR. With the Garmin Vectors, and now supported on the Stages Power meters, you get a slew of messages on the head unit when the batteries are even beginning to get close to needing to be replaced.

Changing the battery

The battery is replaced by removing the plastic cover on the PowerTap C1 chain rings, held in place by 2x screws needing 2mm Allen wrench

PowerTap C1

Inside is the rubber gasket and the CR2032 battery

Powertap C1

OK, we know that Zwift tends to cause the rider to perspire somewhat, so now seems like an opportune moment for a slight over-share of information. The moisture around the gasket in the above picture is actually sweat. Now there hasn’t been any sweat ingress into the actual battery compartment I could see, however, if you are going to be using the Powertap C1 to do a lot of Zwifting, I think it might be worthwhile opening up the case and just adding a little trickle of grease around the gasket as well before you start riding. Just to be 100% nothing is going to get in.

Conclusion

C1 fairs well in terms of being a Zwift power meter – the wattage readings compare directly with another power meter I have used, and. If you have a 5 bolt crank setup, the C1 is attractively priced. If you are on a 4 bolt system, this is not really a device for you.

One thing I was not a great fan of was the FSA mandated chain rings. A lot of similar products such a Stages and Pioneer power meters sell units already attached to components available to match your current components. I think this is quite an important point as I just wasn’t happy with the performance of the C1 rings, either indoors or outdoors.

The signal may not be the strongest out there, but I feel my 56cm signal transmission test might almost be unreasonably harsh. But it is something to keep in mind if you are just sticking the USB dongle straight into your computer running Zwift, plus a stack of batteries might be a good investment too, as I think the 200 hours battery run time is a little…generous

Overall, if you’re running a 5 bolt crank system, the Powertap C1 is a device to consider when you are on a budget and looking to move up to a power meter in Zwift, which you will also use on rides outside

However if your main focus will be to Zwift, you might be better putting that extra money into a smart turbo with a power meter inside.

Staying with that budget theme – the next Zwift Gear Test will be taking the Wahoo Snap for a spin around Watopia!

  • I use a PowerTap C1 extensively on Zwift. It has served me well…until this past week. Two days ago I tried to do a typical workout but had trouble maintaining 250 W for just 4 minutes (my FTP is 268). I assumed my muscles were been fatigued from a gym workout and went to be early the next two nights. This morning, however, the PowerTap failed to sync with Zwift. As soon as I replaced the battery, Zwift detected it.

    Issue 1) My Garmin Edge head unit always gives me a warning when my C1’s battery is low. It doesn’t appear that Zwift reports these low-battery alarms.

    After replacing the battery, my reported power was still low. I couldn’t even generate enough power to get through the warm-up portion of my workout. I had to struggle for even 150 W. I finally turned on my Garmin head unit and hit the “Calibrate” button. For the PowerTap C1, “calibrate” actually means “manually zero.” Presto! My power was back to my typical range.

    Issue 2) Zwift doesn’t appear to provide an option to manually zero or calibrate the sensors it detects.

    Both of these issues appear to be related to Zwift’s integration of the PowerTap C1 meter…not a shortcoming of the power meter itself. I’d be interested to hear whether these issues also arise with other PowerTap meters, and with power meters from other vendors.

    • Unfortunately Zwift doesn’t currently send the signal to calibrate any power meter. Which would be a great thing to see after log in

      However power meters have come a long way now, and we don’t actually need to do a manual zero that often now (although it is reassuring to do so)

  • YamaLink Guy

    I’ve been on the fence about the C1 pm and each time I plan to buy I read comments like yours about chainring shift quality or battery life issues (no warning). Don’t quote me, but some have swapped the sensor to their choice of chainrings with no issues.

    I only use the road bike for mtb racing training so the pricepoint of this product is appealing, but like you and others, when you put so much time, money and dedication into a sport the money “saved” is meaningless if it doesn’t perform as expected.

    Part of me thinks the PowerTap pedals are the way to go but they cost so dang much! Or maybe a PowerTap rear wheel. Oh decisions, decisions. Great review, by the way! Didn’t lose me anywhere in the writeup. My eyes tend to glaze over when reviews get too verbose or technical. Much appreciated.

    • Thanks Yama. I’ve always wondering if I’m going into excessive detail. Nice to know I’m not losing everyone ?