How To Calculate Your Power-To-Weight Ratio
What is the Power-to-Weight Ratio?
The power-to-weight ratio (PWR) is the amount of power that can be produced in relation to body weight, usually expressed in watts per kilogram. It is also cycling’s great leveller, as a measure that allows a comparison of cyclists’ abilities even when the riders vary in size. The higher your power-to-weight ratio, the faster you will go, thus the measurement is also a great predictor of performance.
How to Calculate Your Power-to-Weight Ratio
To determine your PWR, divide the average power from a 20- or 30-minute time trial by your weight in kilograms.
PWR isn’t a static number, but rather corresponds to a specific time span. A rider who averages 6.8 watts/kg for 30 minutes may only be able to sustain 6.4 watts/kg for an hour.
Example: Cyclist A weighs 76 kg and his 20-minute TT power is 275 watts. His PWR for 20 minutes is 3.6 watts/kg.
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For comparison, an athlete needs to be able to produce 6.8 watts/kg in a 30-minute pre-race test in order have a chance at winning the Tour de France. Beginners or Cat 5s range from 2.5 to 3.2 watts/kg for men and 2.1 to 2.8 watts/kg for women; Cat 3 racers typically range 3.7 to 4.4 watts/kg (men) and 3.2 to 3.8 watts/kg (women).
How to Increase Your Power-to-Weight Ratio
The key to getting faster is raising your PWR. As more and more cyclists have power meters these days, it’s easy to monitor the number. But even if you don’t track your watts, you can still raise your PWR just like every other cyclist by lowering your body weight, raising your average power output, or both.
For cyclists who carry around more than 5kg’s, losing weight and gaining power are equally achievable through good nutrition and focused training. Heavier cyclists have the potential to make bigger improvements because they can attack both parts of the equation.
As an example of how small changes can make a big difference, Cheyenne Cañon averages a 7 percent grade for 5 kilometres. If a 75 kg rider with a max sustainable power of 250 watts loses 2.5 kg, that would cut 38 seconds off this rider’s time. Improving power output by 20 watts without any weight loss cuts 85 seconds. If this rider loses 2.5 kilos and increases power by 20 watts, the improvement jumps to a whopping 2:03.
Elite racers aim to be as strong and as light as possible, but this is a delicate balance that can’t be maintained for very long. Most experienced cyclists can expect to see a 15 percent variance in PWR during the year. Because it’s far easier to make the ratio go down than up, changes greater than 15 percent often indicate that you either gained too much weight or decreased your training load too much during the winter. On the flip side, there are physiological limits to how light you can get while maintaining a high power output.
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If you’re leaner than you’ve ever been and your average power output on climbs starts to decline, you’ve reached the tipping point. Try gaining 1-1.5kg, and back off your training a little bit. Your power will likely come back up, and from now on, you should consider this your minimum allowable weight. Future gains in PWR will need to come from better training. Of course, there’s also the weight of your equipment to consider, because shaving grams from your bike will effectively increase your PWR. That said, it’s best to stay focused on your own physiology versus trying to buy your way to an elusive goal as a longterm solution.