Power To Weight- How Pros Find The Perfect Ratio

It’s an obvious equation: basic maths, simple physics. But achieving the perfect blend of power and low body weight is a complex science

- Paul Knott

A badge of honour in cycling, power-to-weight ratio is a critical determinant of performance. In simple terms, it is a rider’s maximum sustainable power divided by their weight, usually expressed in watts per kilogram (W/kg). Power-to-weight (abbreviated to PTW from here on) is least relevant in short, flat events, where the battle is between the burly sprinters, those riders who can produce the highest peak power. It is most relevant on long climbs: climbing specialists need plentiful power and minimal weight to overcome gravity. So, just how much should you care about your own PTW figure? At what gradient does PTW trump outright peak power? Daniel Green, performance analyst for Team BMC, explains: “You are looking at the relationship between the effort the rider has to make to overcome the resistance from the air, compared to the effort they need to make to overcome gravity.”

The biggest challenge on the flat is pushing through the air, while the key factor on a climb is gravity.

“As the gradient steepens, the velocity reduces,” Green continues. “On a 10 or 12 per cent gradient, velocity may only be 16 or 18kph, so air resistance is negligible but gravity is dragging you back. Not until the gradient flattens to five to six per cent does gravity, and therefore weight, become less important.”

The influence of weight is clearly a huge factor in climbing, and minimising the total weight that you have to haul up a climb can be achieved in a number of different ways. One relatively painless, though often expensive, way is to modify your bike. Former national hill-climb champion Tejvan Pettinger highlights the effect: “Being one kilogram lighter may save two seconds on a short climb, but the margin of victory can be very narrow in national championships, so even one or two seconds is important.”