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!
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
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
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.
Inside the box, we’ve obviously got the PowerTap C1 itself.
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.
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
Finally, there is the actual black box of the power meter, attached to the chainring
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)
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
Then slotting everything together – whereupon everything, unsurprisingly, lines up very nicely.
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
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!
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)
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
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
- 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
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
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
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.
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.
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
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
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
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 good
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
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
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
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.
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
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
Inside is the rubber gasket and the CR2032 battery
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.
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!