How much power are you throwing away?
I am informally coaching a couple of other cyclists in my area, one of whom I sometimes hook up with the Garmin Vector 3 pedals I own to get some in depth data on the cyclist’s pedalling technique. This reveals some interesting, and frankly quite shocking numbers that I found hard to believe at first.
I have spent a long time working on pedalling technique, and have developed my pedal stroke so that when I am putting out high power I might lose about 5-8W through what is called ‘GPA’ (gross power absorbed) which basically means not getting your feet out of the way of the upstroke in the pedalling circle, and therefore pushing down against the pedal very slightly with the foot that is coming up. I strive to get it lower but this seems to be about as good as I can get it for now. Interestingly, the figure goes up rather than down at lower powers – at around 300W it’s about 6W GPA but at 150W it’s about 12-15W. Interesting, and something to work on.
However, check out this picture. This is taken from the ‘Pedalling Metrics Review Pack’ in WKO4, which you can use with any power meter that generates the data for it, such as Garmin Vector pedals.
This shows the plot of an FTP test recently performed by the cyclist in question. Ignore all the madness in the top pane, look at the bottom pane. This shows GPR (Gross Power Released, or power generated by pushing on the pedal) for the two legs in the red and blue lines, and GPA (Gross Power Absorbed, already explained above) in the green and purple lines. Now this person’s FTP for this test was 102W. You can see the 20 minute FTP interval slightly to the right of the middle. During this interval, the rider is putting out on average 108W, but break that down. Look how much is being absorbed – on average around 30W. This means that about 138W is being generated via GPR and 30W is being lost in GPA. That is a massive loss, almost a quarter!
Let’s say the cyclist improves their neuromuscular coordination by focussed pedalling practice, and reduces GPA to 10W. This means they are now putting out 138W – 10W = 128W. That is an 18.5% improvement in power output – for 20W, or 14.5% less effort! You could then theoretically add that 20W to the GPA for the same effort and end up putting out 148W instead of 102W. That is an unbelievable amount of improvement, and it’s all just sitting there ripe for the picking. Work to be done!
If you look to the lower power sections, the power loss is actually higher even though the wattage is lower, so the percentage loss is much higher. I have noticed this as well in my own pedalling as already mentioned above.
This goes to show how useful Power Meter pedals can be when paired with the right software. WKO4 I have found to be almost unbearably slow, even on a decent spec i7 PC with 16GB RAM, but it is an very powerful tool once you get to know it. This is just one example of how you can use hard data to improve your riding, and ultimately, your speed down the road.