A common question that I get is what is a better power meter- “the power tap or one that’s in the cranks?” This is a great question, especially considering the cost of a power meter. I will attempt to answer this question here.
There are usually two questions about which power meter is the best:
1. Which is more practical, having it built into the bike or into a wheel?
2. Which is more accurate?
For which is more practical, that is fairly straightforward…
For a Powertap, the power meter portion is built into the hub, that has to be built into a wheel, whether it’s a training wheel or race wheel such as a Zipp, that is up to you.
The main advantage of a Powertap is that you can switch it from bike to bike (road to TT or vice-versa), simply by switching out back wheels and attaching the computer to the other bike.
So if you’re like me, you don’t want to be out training on a $2000 set of race wheels, which makes it a more expensive purchase to have two (2) Powertaps, one in a training wheel and one in a race wheel.
For the Quarq, the power meter is attached to the chain ring of your bike and measures power from the tension put on the cranks as your pedal.
You can use whatever rear wheel you want, training or racing, without having to worry about where the power meter is located.
It’s not easy to move the power meter from one bike to another; it usually requires a mechanic, which can cost $20-100 to switch it from bike to bike.
So what’s the bottom line? A Quarq cost $1850 with a Garmin 500 through Break Through Multisport. One Quarq, one bike. A Powertap costs $1100-1600 through Break Through Multisport, but you only get one wheel.
So, if you have a road bike and a TT bike, and race with race wheels, you are looking at the following costs to cover all of your bases:
Quarq: $1850 (Quarq + Garmin 500) + $1550 for second Quark (you won’t need a second Garmin 500) for a total of $3400.
Powertap: 2 x $1100 – 1600 (Powertap built into training wheel) for a total of $2200-3200 plus the cost to build the hub into a race wheel, which is usually an additional $150-200 depending on your bike shop.
As far as which power meter is more accurate, that is a misleading question. As long as you are using the same power meter, it is as accurate as you will need it to be since the data will be consistent for that device!
For example, if you do a 20k time trial to test your functional threshold power (FTP) with a Powertap one day, a Quarq the next week and a CompuTrainer the week after, the numbers might be different, but that doesn’t matter as long as you can remember the correct numbers for each device. For example:
20k TT with Powertap: FTP is 220 watts.
20k TT with Quarq: FTP is 235 watts
20k TT with CompuTrainer: FTP is 200 watts
So what does this mean? It means you need to remember the FTP for each device in order to make sure your training zones match the prescribed intensity that your coach is asking you to ride at.
For example, if your coach asks you to complete 8 x 5 minute intervals between 91-105% of your FTP (Z4- Threshold), the numbers would look like this for each device:
Powertap: 219- 231 watts
Quarq: 213-246 watts
CompuTrainer: 182-210 watts
So if you own a Quarq, your range is 213-246 watts (Z4). If you rode that on a CompuTrainer, and rode between 213-246, you are now riding at 106-123%, which changes the training zone from Z4 to Z5, which is hitting a different energy system and defeating the purpose of the workout.
If you rode the same workout on a Powertap, without adjusting the FTP numbers, you are now riding at 103-111% of FTP, which is at the very high end of Z4 into the middle of Z5.
The key thing to remember, you need to have a different FTP for each power meter that you own/use. You will also need a different FTP test for indoor trainer rides and for outdoor rides if you are using a power meter that is built onto the bike instead of a CompuTrainer.
I hope that you find this information helpful when deciding which power meter is the correct one for you. If you have any further questions on training and racing with a power meter or if you are interested in purchasing either a Quarq or Powertap at a discounted rate, please contact me.