If you type “Powertap vs. Quarq” in to an internet search engine you will get tone of results on this topic and all follow the same lines, basically cyclists who are looking to invest in powermeteres to improve their training but are undecided on which product to go with. Most have generally decided that an SRM is too expensive and is not included in the equation, so this means they are left with the 2 best consumer powermeteres that are currently available on the market today: A Wireless Powertap or a Wireless Quarq Chainset.
As I am lucky enough to be the owner of both of these power measuring devices and have been using both for some time, I feel it my duty to help those of you who are in this predicament with my views on each product and which I feel is the one that I would keep if I had to get rid of one. This is a direct comparison of a 2008 Powertap 2.4SL ANT+ Wireless power meter that I brought direct from Bontrager and is built in to a 2009 Race X Lite Aero wheel and a 2010 Quarq SRAM S975 Wireless Chainset and not a generalised review of the companies or of the products that they produce. This is purely something that I feel compelled to share with other and I am in no way endorsed by either company in order to provide a biased view, these are my own thoughts and my own conclusions and you can either take them on board or dismiss them as you wish, I just love to write about power meters and there related subjects.
The Technical specification of the products
Category | Bontrager Powertap 2.4 sl | Quarq SRAM S975 |
Price (at time of purchase) | £1499.99 Complete Wheel with Cyclops CPU head unit, HR strap and software (2008) | £1349.99 Chainset only. (not including head unit, HR strap or software) The 3rd party accessories I use are Garmin 800 - £310.00 HR Strap - £40.00 GXP BB – 29.99 Total Set up cost - £ 1729.98 |
Accessories | CPU head unit HR Strap Power agent Software Cap removal tool Carry case Download cradle Installed batteries | Installed batteries Spare battery cap 3 magnets Adhesive putty |
Added weight to standard Product | 412g Total product weight – 1407g | 124g Total product weight – 884g |
Wireless Technology | ANT + | ANT + |
Calibration | Factory Process | Factory Process, although software is being developed to allow user to calibrate slope at home. |
Battery replacement | User replaceable | User replaceable |
Claimed Accuracy | +/- 1.5% | +/- 2% |
Measurement | Hub – 4 strain gauges | Crank spider – 20 strain gauges |
First time set up
Powertap.
One of the big advantages of the powertap is the ridiculously easy initial installation. If like me you buy the hub pre built in to a wheel then all you have to do is simply slap the wheel in to your bike, attach the computer mount, pop in the head unit and that’s pretty much it as far as bike installation. You don’t have to install any speed or cadence sensors as all of this measured from the hub including the cadence which is measured through what Cyclops call virtual cadence. This is done by calculating where torque is being applied to the hub and at what frequency, sounds sceptical but in my experience its works very well with only the occasional spike.
The manuals are detailed and easy to understand which is good as setting up the head unit can be a bit of a faff due to the lack of buttons and screen space meaning that all of the settings must be done through the use of various button combinations and on screen abbreviations. However, the setting are detailed and allow for a good customisable set up such as choosing the smoothing rate of the power update and which metrics you want displayed on the main screes. The hub found the CPU within a minute and stores the ID so it picks up even faster in the future.
Quarq
The first thing I noticed when I received my fully packaged crank set was the lack of weight, it is impressively light adding almost no weight to the standard SRAM red cranks. Installation is a bit more technical than the PT but as long as you are fairly mechanically minded it is simple enough. It’s basically the same as installing a standard chainset; Install the bearings first, pop the spindle through and attach the non-drive side crank and tighten to the required torque. The only difference with this chainset is the need to install a small magnet behind the cranks; this is what triggers the read switches and is a key part in the power measuring method. This can either be easy or hard depending on your frame. If you have an external BB then you can use the supplied bracket which simple sits behind the BB when tightened and houses the magnet which is already positioned where it needs to be. However, if like me you own a frame with press fit bearings, the fitting of the magnet requires some creativity. Quarq do supply adhesive putty but I used a mix of rubber patches, super glue and Mastic Glue. This has proven solid so far and very weather proof.
As the Quarq doesn’t come with a head unit, it requires you to use a 3rd party computer and the most obvious choice is the Garmin which is what I am using. This requires no speed sensors as it calculates it of off GPS, cadence is taken care of by the magnet that you installed and the computer Is a fantastic training tool with a huge range of features, to many to mention here. Set up is much easier than the Powertap CPU due to the touch screen navigation and large display, the Garmin picked up the Quarq in less than 30 seconds and again stores the ID so as no cross interference occurs
Calibration Process.
All power meters require you to calibrate them before you set off on your ride. This process must be done to ensure accurate reading and essentially what you are doing is storing what is known as an offset number, this is like a starting point for the power measurement and allows for reliable readings.
The Powertap calibration process is simple enough and has the added bonus of being able to see the actual torque of the hub in real time, this means that users are able perform such things as stomp tests to see if there hub is working correctly, search stomp test to understand more. Before a ride calibrations takes about 30 seconds once the hub has woken up, the PT has the added feature known as auto calibration. This is where the hub will continually re calibrate itself whilst you are riding to ensure power measurement remains consistent as sometimes offset can drift, mainly due to temperature changes. It does this every time you freewheel which is great as you don’t even have to think about it during a ride.
The Quarq also requires a pre ride calibration and is done by waking the cranks by spinning the backwards, placing the drive side arm at 6 o’clock, and going through the setting on the Garmin before pressing calibrate. The Quarq will the return an offset number which should be between +500/-500 nm, this will vary from day to day but eventually it will stabilise around the same figure but providing it is with in those limits then all is fine. The key thing is to make sure that the offset hasn’t shifted by more than 50 points during your ride, if you do feel that your power has changed during ride such as reading low then you can auto calibrate by pedalling backwards. This is not as seamless as the PT but does work great every time. The Quarq is more susceptible to offset changes due to its sensitivity, especially to temperature so it’s best to auto calibrate often during your rides. Once you get in to the habit its fine and now I am finding that I only need to do it once or twice during a training ride.
User friendliness and reliability
Power meter are expensive and when you are parting with a big lump of cash you expect the product to be of high quality and not suffer from to many technical faults or issues. Here is a rundown of how user friendly each power meter is and what problems I have experienced with each.
Powertap
The powertap doesn’t require much maintenance over what you would give your standard wheel, look after it and it should be fine. The PT has user replaceable batteries which are a must as you don’t want to have to ship it off every time the batteries die. The process of changing the batteries isn’t too difficult but does require a specific tool to remove the hub cap and to be honest the first time I had to do this I was extremely nervous and wasn’t entirely sue if I was doing it right. The manual’s instructions are a bit vague and I had to do some forum searching to make sure. However, once I had done it once it’s a synch. The only other aspect of the hub which will tire and need replacing are the hub bearings and if you have done your research you will already know that this is a huge fault with the PT and caused me a huge amount of grief in the past. The bearing that Cyclops put in the hubs are rubbish, there’s no other description. I don’t know why but they wear out in a few months and not subtly either, one day they will be fine and then the next day your when will be moving a few millimetres from side to side, not good. Worst of all is that Cyclops state that the bearings must be replaced by their technicians, this isn’t entirely true but I will come back to that. So the first time my bearing went, the UK didn’t have a service centre, this meant that I had to send my wheel back to the us to have the bearing replaced. 6 WEEKS, 6 weeks went by before I got my wheel back, this was the most stressful time ever and was not a pleasant experience. The whole point of this piece of kit is that you use it every ride and being without it for that long can really mess up you data history. I was not impressed. Thankfully, Saris have set up a UK service centre which is good because only a few months after I had new bearings, it had to go back for more. This time the process was only a few days and they guys also replaced the axel with the newer 15 millimetre one and also re calibrated it. Great, or so I thought. I got the wheel back but noticed there were still huge amounts of play in the wheel but it wasn’t coming from worn bearing but instead the axel had play in it. This meant the wheel had to go back again, so another week went by with no wheel but they did solve the problem and got it back as fast as they could. For a good number of months the PT had been functioning faultlessly until very recently when the bearing when again. However, due to the wheel being out if warranty the bearing replacement would cost me about £60, I did some research and discovered that over time various people discovered that you could replace the bearings yourself without the need for shipping back. I found a bike shop that had done a few and the process took 2 day and cost me £30. Now that I know this it takes a lot of the worry out of the equation. Just remember that if it does go wrong, your warranty is void and a new toque tube will cost you about £300, so make sure you trust the person doing it.
Quarq
Like the PT, the Quarq features a user replaceable battery only it’s much easier to replace than the PT. it’s simple a screw on cap that sits on the outside of the crank and takes about a minute to change. The Quarq trumps the PT in that one for sure. Other parts that may need to be replaced include the BB bearing; however this is just the same as any other bike and requires nothing specific and also you will eventually need to replace the chain rings when they wear out. Quarq recommend that you send the cranks back to the factory once you have replaced the rings as it will need to be re-calibrated, this is a bit of pain but thankfully this can be done through the UK SRAM service centre, although there have been reports that people have replaced the chaining’s and not needed to send them back but personally I would send them off just to make sure. Now, I have only had my Quarq since September 2010 and I will be honest with you, I am on my 3 set already but before you dismiss this product let me explain why. The first set I received were an early 2010 model, I began using them and done a lot of research in how to use them with best practise as far as the calibration was concerned. As I have mention, the initial offset should be within +/- 500 which they were, however, the offset should not shift more than 50 n/m during a ride and in this case something was wrong as mine were shifting by over 100 in some cases. I traded various emails with Quarq to try and solve the problem and here I will say they Quarq have the best customer service I have ever received bar non which is very reassuring. I was told to try re-torqueing the chainring bolts to 10 n/m, but this didn’t help. Eventually I pinpointed the problem, a missing screw on the back of the power unit. Because this was clearly a warranty issue I had to send it back to the shop I sent it through who then sent it on for repair, this whole process was done with is a week and received my chainset back which had been fitted with a brand new power unit. I fitted the cranks to my bike, tried to pair it with my Garmin and………..nothing. There was no life in the cranks; I tried replacing the battery but still nothing. I contacted the man at SRAM who serviced my cranks and he had no idea why it didn’t work, this meant that I had to send the cranks back again, I was informed a few days later that they couldn’t find out why they weren’t functioning and that they would send me out a brand new set rather than trying to repair them again. The process was again complete with in a week and I have been enjoying perfectly functioning cranks since. I must reiterate that the customers service I received during this time from Quarq, SRAM and the shop I purchased the cranks from was exceptional, Cyclops have very good customer service but Quarq’s is second to none.
As you can see, you may be parting with a lot of cash but power meter are still relatively new and there are still a lot of issues that need ironing out. Yes I have had to send both power meters back to their respective service centres 3 times but no I didn’t once regret buying either at any point. Just be prepared to be without you power meter as some point irrespective of which you decide to but both are delicate pieces of technology and at the end of the day, technology always has a habit of going wrong.
Overview
Powertap
Firstly the power powertap is amazing value for money, you not only get the power measuring hub but also the CPU, HR strap and software meaning that once you receive you PT you are set ready to go without the need for anything else. One of the biggest advantages with the PT is the ability to switch it between bikes extremely easily; all you need is a few computer mounts for your individual bikes. However, it does leave you with the nasty decision of what wheel to have your hub build in to and when and when not to use the wheel. If you get it built in to a training rim to use for training, this means that if you want data from races you will also have to use this when rather than your flash, light weight carbon clinchers. If you do it the opposite way, you will have to use your best wheels for training meaning they are going to get a lot of winter wear. You could get 2 hubs and build one in to each kind of wheel but this makes it very expensive. I have used my PT in all weather conditions and only ever once had an issue where water has gotten in to the battery compartment and caused the power to stop reading, once it had dried out it was fine and hasn’t happened since. I now always make sure I put weather proof grease in the hub cap seal whenever I remove it.
Quarq
A shade under £1400 might seem like a lot for a power meter when you compare it to the PT and realise that you don’t get a head unit, HR strap or any other software with it. But when you compare it to its closest rival, the SRM, it represents amazing value for money as if you were to buy the equivalent SRM you won’t see much change from about £4000, admittedly you do get a CPU and training software but if even buying the Quarq with a top of the range Garmin head unit which offers the most information of all of the cycling computers on the market and also taking in to account purchasing WKO+ which is considered the best training software available, you are still getting a package that could be considered better than the SRM for less than £2000. When you look at it this was it suddenly seems like a very good buy. As with any crank based power meter, swapping the chainset between bikes is a bit more involved that with the PT but it can still be very quick; I saw a video on YouTube of a rider swapping is Quarq between bikes in less than 30 seconds!
The one thing that I can say about the Quarq over the PT is its overall robustness, the Quarq just feels so much more solid than the PT and a lot less vulnerable to damage in a crash, although I have crashed a few times with my PT and haven’t had any issues. But if you think how vulnerable a wheel can be in general such as buckles or bending spokes, it does make you ride with caution all of time, especially when racing. With the Quarq I don’t feel the same worry as it feels more a part of the bike rather than just an add on. It also feel stiffer and have always felt that my powertap wheel was sometimes rather heavy and sloppy, although I suppose this depends on what wheel you have it built in to. The Quarq claims to be extremely weather proof and have proved it by supplying cross riders with chainset to use during some of the muddiest cross races during the season and have had no problems.
Out on the road both power meters have performed pretty much faultlessly. Having come from using the powertap for a long time before switching to the Quarq I have noticed that the Quarq is a lot more responsive to changes in power than the PT. according to other source the Quarq updates somewhere between 3-4 times per second depending on cadence whereas the PT averages the samples out over a second and then updates to the head unit. It took some getting used to but I do prefer the faster sampling of the Quarq now I have used it more and depending on what head unit you have you can smooth out the sampling rate to make it smoother, I run a 3 second sampling rate which means it averages out the power over that duration and then updates the head unit, this is still visibly faster that PT.
The one big thing that I will say about the PT over the Quarq is the lack of attention you have to pay to the offset and calibration out on the road, because it does it all for you whenever you free wheel you don’t ever have to think about it, this can also be a negative as you can never quite tell if the offset has shifter during a ride unless you spot tell-tale signs. The Quarq is also a lot more sensitive to changes in tempura than the PT and this is mainly due to the amount of strain gauges it uses and just how sensitive they actually are. This means that I have noticed changes in off set a lot more than with the PT meaning that I have had to consciously back pedal in order calibrate on the road, not quite a seamless as the PT but does its job fine.
Comparing ride data
Not all power meters are created equally and this is especially true with the PT and the Quarq as one is hub based and one is crank based. The Quarq has the benefit of being a direct drive measuring power meter which means that it’s measuring the power that is coming directly out of your legs. The PT on the other hand will generally measure slightly less due to power being lost as it travels down you transmission and in to the hub, this is exacerbated if you drivetrain is in bad condition. This scenario can cause some riders concern if they are planning on using both power meters throughout the season, the difference could be up to 10 watts in some cases and when talking about power, 10 watts is quite a lot.
I decided to do some first-hand testing to see how the ride data for both units compare and I ended up with a pretty interesting analysis. I put my PT wheel in the same bike as the Quarq, Paired the Quarq to the Garmin first and the paired the PT to its own CPU after, I then rode to the power from the Quarq which is displayed on my Garmin and had the PT CPU in my pocket. I rode out at a steady level 2 pace and the did a few 20 minute threshold intervals before heading back, as the PT would have been auto zeroing its self during the ride I decided to make it comparable by auto zeroing the Quarq a few times as well so as to see if any big changes appeared in the results.
Here is the data from the ride for both units as displayed by WKO+
Data Field | Quarq | Powertap |
Ride time | 2..45.00 | 2.45.00 |
Average Power | 220 watts | 225 watts |
Norm Power | 235 watts | 233 watts |
TSS | 204.2 | 206.4 |
Max Power | 619 watts | 606 watts |
Average Cadence | 76 rpm | 77 rpm |
Work | 2153 KJ | 2155 KJ |
20 min Interval 1 Ave Power | 263 (22.1 mph) | 257 |
20 min Interval 2 Ave Power | 263 (22.0 mph) | 259 |
20 min Interval 3 Ave Power | 264 (22.0 mph) | 267 |
So from the ride data we can see that the entire ride metrics come out almost exact with the PT reading a few watts lower which as I have already said is to be expected. However, when looking at the individual interval we can see that whilst the Quarq’s averages come almost identical over the 3 efforts, the PT starts off reading 6 watts lower, it eventually ends up reading 3 watts higher that the Quarq by the 3rd interval. I auto zeroed the Quarq after each effort to ensure repeatability and can say that my RPE during the efforts only increased due to the expected fatigue experienced over the session, also note that the average speed from each interval sits perfectly with the power and as these efforts were done around a 20 minute loop with no changes in weather conditions, this metric can be considered a pretty reliable indicator during this session. With all of this in mind it appears that throughout the session the PT was steadily rifting upwards and possibly over recording power towards the end of the session, or maybe it was under recording power at the beginning of the session. This is something we will never really know but what would be interesting is to go out and do a similar ride but riding to the powertap and seeing how the Quarq’s power shifts throughout the session, although my personal feeling are that it wouldn’t proving you auto zero occasionally. This is something that I will do and will update you all on the results as they could prove interesting. Ultimately though, having used the PT for the previous 2 seasons, I can say that I have never really experienced any noticeable shift in power during repetitive intervals so even if it has it has never been enough to really effect the accuracy of the session. With anything like this, it depends on how much difference a few watts are going to make to you. For a 20 minute interval I feel that a drop or a rise in 5 watts wouldn’t affect the quality of my intervals too much.
Conclusion
So, this is the tricky bit. Which power meter would I recommend for a power training virgin who was looking to take the lunge and buy in to this amazing advancement in cycling technology? Well there no doubting that both units have the strong points as well as their flaws but thankfully these flaws aren’t enough to warrant no buying one of the other. It very much comes down to preference and you own situation. If you are going to be continuously swapping bikes then the PT is the obvious choice due to how much easier this is. But if you plan to keep it on one bike which you will use for training and racing the crank based system is the winner due to being able to chop and choose your own wheel. For most people it will all come down to costa and at the moment you can’t buy a cheaper complete unit that the PT as it comes with everything you need to get you started. The thing is though, as you become more involved in training with power the chances of wanting to upgrade your head unit and training software are likely so you end up forking out for these items in the future anyway. The Quarq doesn’t come with any other kit so if you have nothing at the moment the initial outlay is more than buying the PT but still hugely cheaper than a complete SRM system. If you do already own a Garmin or other ANT+ compatible head unit then I would say there is only one choice and that’s the Quarq.
Both units have their technical issues and I have experienced first-hand what can go wrong although it does seem that the PT needs more work when it comes to general maintenance due to the bearing, free hub etc., I can’t ever see myself having to send my Quarq back very often due to standard wear and tear so for user longevity I would say Quarq wins that round. When I have had to send my units back to their respective service centres I got to experience the company’s customer service first hand and I am pleased to say that if you are planning on shelling out £1500 for a power meter, the customer service is well up to standard and you will have no issues in this respect which is very comforting.
So overall, both are great units, both are great value in their own way and both will do everything that you could ever want from them. But if you were to ask me which one I would keep if I could only have one then I think I would swing in favour of the Quarq. My main reason for this is that a crank based unit suits my needs more than a wheel based unit as I will only be sapping it between bikes 2 a year, once to change to my winter bike and once to change back to my raining bike. During the season it will stay on my raining bike and I will have the choice of what wheel I can use depending on the parcours of the race. I also feel that the Quarq is more robust that the PT and less likely to be damaged in the event of a crash and isn’t susceptible to silly little things like a buckled wheel or broken spoke like the PT is. Accuracy wise there is very little to choose between them, yes the PT displayed some drift during my testing but like I say I have rarely being able to see this myself before the test so don’t let the factor of accuracy or repeatability come in to you decision, it’s not something you really have to worry about.
I hope this review has helped you in some way if you have been torn between which unit to buy; either that or I have just made you change your mind for the 100th time. Things aren’t going to get any easier in the future either as a new wave or power meter begin to make their way on to the market, the most interesting ones being from Garmin/Metrigear and Polar/Look who are both racing to be the first to officially release the pedal based power meters on to consumer market. Both are in the testing stages at the moment and are expected out towards the end of the year, they are reportedly going to be retailing for around the £1000 mark but what this will include is anyone’s guess. Expect another power meter review on here in about 12 months’ time after I have brought myself a pedal based unit as well!!!!!
Feel free to ask any questions related to this topic by simply adding a comment, I would be more than happy to respond.
Train Smarter, Ride Faster. Simple.
Dan
Thank you for this excellent review. The precise and detailed technical information is exactly what I was looking for when making a decision on power meters.
ReplyDelete