Lastly, here is a zoomed in graph at the first interval. There is a large initial overshoot of power and then the power levels out fluctuating around the target power. The second interval shows less of an overshoot and a steadier power through the interval.

One feature that I do enjoy is that since the power is measured at the spider, the DFour can determine the power output of each leg. Seeing the power balance is a great way to make sure

5 Great Features

1) Ability to measure power from each leg. Since the power is measured at the spider, the DFour can determine the Watts each side produces. The power balance can be seen in post analysis. This is good to see if there are any discrepancies in strength between each leg.

2) Stiffness of crankarms. I have put over 1500 Watts and had no issues and the power transfers instantaneously to the bike frame.

3) Durability. Since the crankarms are made from aluminum alloy the are very durable and I have no worries if they are to get banged around

4) Stylish looks. These cranks are very aesthetically pleasing. The probably look better with Dura-Ace chainrings but the glossy black finish is very sleek.

5) Battery life. I’ve had various other power meters and it seems like I am constantly changing the batteries. The DFour has lasted many hours of riding and the battery door is very sturdy.

POWER METER ACCURACY

We must face it, power meters are not accurate, thus the need for a claimed +/- # accuracy rate, but the lower the accuracy rate the greater confidence one will have in the device. Yes, Strava can provided estimated power that are “close enough”, but those values are empirically derived from thousands of hours of user power data and heart rate data. Thus, a power meter with a slightly worse accuracy rate, say +/- 3%, may still provide better results than estimated power Strava.

To my next point though, accuracy is not the most important thing of a power meter, but that it is giving you consistent power values day to day (precision over accuracy). If you are using a training plan based on your functional threshold power (FTP), the goal is to increase you FTP. If you are following your properly designed training plan and your power meter consistently gives you precise power values, that is most important. In other words, does it matter if your FTP is 300 W, but your power meter tells you it is 305 W, 325 W, or 275 W? No. Training properly with a consistent power meter will result in an increased FTP, and the subsequent FTP test will undoubtedly be higher.

Not to get too deep in to training theories or what the best method for training is, training based off FTP is probably one of the most used methods. Training off FTP has flaws, and FTP is only a single parameter and does not tell you the whole story. Thus, the stability of a power meter over a long period of time is what one would most desire. There are plenty of scientific studies comparing commercially available power meters, and these studies have found variations between individual power meters and have found larger variation when comparing different power meters.

When comparing two power meters (two power meters on a single bike), one would hope similar trends (e.g., large spike when starting a sprint). When comparing two different power meters one must realized that different companies use different methods for calibration, so a small variation can be introduced here. The location of where the power is being recorded (e.g., pedal based, crankarm based, spider based, hub based, etc.), typically results in a different power value, but if the calibration is based on forced applied at the pedals, then theoretically the power reading should be the same.

One thing that should be noted is that a power meter does not directly measure force. Power meters use strain gauges to measure a change in voltage in the electrical circuit. When a force is applied to the pedal, the pedal spindle/crankarm/spider (depends on where the strain gauge is placed) is stressed and is deformed. These deformations stretch, shrink, or twist the strain gauge causing a change in the resistance of the strain gauge. Through a calibration process, power is derived from the relationship between the force applied and the voltage change.

The last thing to think about is in what range is the stated accuracy rating accurate for. If the stress strain curve of me crank material is linear, one should think that this accuracy rating is good for the entire service range. If most of your power work is in lower watts it is possible that the accuracy is greater than if you are doing higher power efforts. Also, it is possible that steady cadence will provide better results than doing a lot of surging. Without more information from the power meter companies, or some sort of standardization on how accuracy is defined and how calibration is performed, different power meter will always have variations between them.

Many power meters have some sort of temperature compensation, and one would assume that during the calibration stage this is considered. But like in scientific studies, these are ideal lab situations, and things are different when they are subjected to real world conditions. It is safe to assume that most power meter will be well behaved over the short term and if one is performing FTP test regularly, then power accuracy is less of a concern and the precision is more reliable. Accuracy is only a concern if one is bragging about their FTP and, in reality, one should keep that number private.

Final Thoughts

I have owned power meters in the past, and to date this SRAM Quarq DFour power meter has given me the least amount of trouble and in fact I have not had any issues with it. I have had plenty of hours on it and I am still on the original battery. I have not had and connection or drop connection issues. No issues with water intrusion. I can be confident is saying that it is very reliable, durable, and consistently provide good data.

Author Conflicts

With this being my first power meter review, little other data comparable data collected, and it being the newest and most recently calibrated, in future test it will be my baseline to test other power meters against. Soon I will be reviewing a Kinetic R1 Smart trainer and compare results to it.

I purchased the products with my own money. I did not receive any compensation from SRAM or Quarq to review these products. These products were reviewed on my own accord to provide information about the product and hopefully provide useful information to help guide you in deciding to purchase the product.