The speedometer can tell you the actual speed, but it cannot indicate how much effort is used to travel at that speed. When you are moving fast, it can be due to you pedaling hard, or it is just the benefit of having a good tailwind. On the other hand, when you feel that you are moving slowly even though you are putting in considerable effort, it can be due to tiredness or something else (such as slight uphill, slight headwind or rubbing brakes, for example).
With a powermeter, it will be easy to tell the power required to sustain a certain speed. Most people use powermeters for training purposes, so that they can gauge their effort and stick to their training plan. However, I only intend to use it to collect some data, not for training.
There are many brands and types of powermeters available, such as pedal type, chainring type, rear hub type, crank arm type, etc. I decided to get a simple one-sided powermeter, as I don't need the accuracy of a dual-sided powermeter.
For one sided power meter, Stages and 4iiii are the more popular ones available, with a similar cost. Stages came out with the left crank arm powermeter first, but they have been having some quality issues from what I heard. Therefore I decided to get the 4iiii power meter which is also a left crank arm type.
Installation is as straightforward as it can be, as you basically just replace your existing left crank arm with the one from the 4iiii factory, which has already been fitted and calibrated with the strain gauges on the left crank arm. It is also possible to send in your existing left crank arm for them to install the power meter, but that may be too much trouble especially if you are located halfway around the world.
4iiii Powermeter, which claims to be the lightest left side powermeter.
Set up instructions are printed on the inside of the box.
As I plan to install the powermeter on the Canyon Endurace road bike, I got a crankarm that matches the groupset. As already done earlier, the Dura-Ace R9100/9170 groupset has already been installed on the bike, therefore I need to get the model that uses the Dura-Ace R9100 left side crankarm.
When I ordered the powermeter, the crankarm was not in stock, so I had to wait about a month before I received it. Here it is!
Dura-Ace R9100 left side crankarm
Super glossy surface finishing as seen here
4iiii sensor glued to the back of the crankarm. Most of the bulk is actually taken up by the coin type battery.
Relatively low profile, should clear most chainstays, unless your bike has a special chainstay profile.
165mm length to match the right side crankarm
Battery cover taken off to show the battery. Easily replaceable when it runs out of power.
Weighs 182 grams including the sensor! The regular crankarm without the sensor weighs 173 grams, so the sensor weighs just 9 grams. Super lightweight powermeter indeed.
Sufficient clearance between the sensor and the chainstay.
Installation is easy, just use this crankarm with powermeter instead of the normal one that comes with the crankset. After that, link it to your cycle computer via ANT+, then calibrate and zero the powermeter as per the instructions.
From the data, I can see that it takes roughly 130 watts to pedal at 30km/h on the Canyon Endurace, on flat ground and no wind, and without drafting. To go at 40km/h will require about twice the power! I can only sustain this power over a short stretch.
Pro cyclists regularly cycle at over 40km/h, which means that their power output will normally be 200 watts or more. This is already accounting for the drafting effect when riding in a group.
In a way, having this data helps you judge your pedaling effort and how much more you need to go faster. For example, if I want to sustain 35km/h instead of 30km/h, I will need to raise my power output from 130 watts to 180 watts! That is a big jump and it will take a lot of training to sustain this power for a meaningful amount of time.
However, if you are drafting, you can save about 30% of your energy if you do it correctly. Therefore, if you are drafting behind somebody, you can go at 35km/h while using about 130 watts. In other words, if you can output 130 watts, you can ride at 30km/h solo, or 35km/h when drafting.
The best part about this powermeter is that it is super low maintenance and fuss free. The battery lasts a long time, and there is no need to calibrate or pair it every time you ride. It is also very lightweight and small sized, and is hardly visible on the bike.