What is the power to weight ratio?
Power to weight ratio is exactly what it sounds like. It is a measure in watts created in relation to a rider's weight in kilograms. Cycling is a sport of relative output (raw output would be who can create the most power, whereas relative is who can create more power for a given size). This equation is very simple to calculate. For instance, take a given output of power over a 5-minute period. Divide this value by a rider's weight in kilograms. Ie: CP 5 of 400W / 70kg rider = 5.71W/kg. In theory, a 60kg rider would need to create 342.6W to ride at the same pace as the 70kg rider, but we will see this is not always the case…
How can we use Power to Weight?
Power to weight can be used to estimate performance. There are standard performance benchmarks created from power to weight about what division/race preformance one can expect for a given power-to-weight ratio. For the most part, these are a good measure of general performance, however, there are a number of instances where power to weight should not be the focus.
Power over Weight...
A major concern of power to weight is the focus that developing athletes (youth and masters) put on power to weight ratio. To much focus on the weight aspect of this equation can derail development (especially limit power production) and lead to unhealthy habits that spill into life off the bike. Athletes should focus solely on the POWER side of the equation for as long as possible. More power will always provide better results in the long run. Restrictive dieting will impair recovery, limit training capacity, and can lead to an unhealthy relationship with food with the possibility of long-lasting negative side effects. By focusing on quality training and recovery, power output can steadily increase for years.
Bikes % of body weight.
Race bikes are more or less the same weight. Road bikes are limited to 15lbs (6.8kg) and XCO bikes typically weigh between 20 and 24 lbs. Time for some math…. When considering power to weight ratio, it is important to consider the weight of the bike! Bike weight will represent a greater percentage of body weight for a 60kg athlete compared to a 70kg athlete. With this in mind, lighter athletes will need a greater power-to-weight ratio than heavier athletes to ride at the same speed due to bike weight. By placing too much emphasis on weight, athletes sacrifice power and can reduce power to weight when you consider the bike weight into the equation.
Flats
While power to weight does play a large part in climbing performance, it is important to consider the flat sections on the course. Raw power and aerodynamics are far more predictive of speed on the flats. For example, a 70kg rider may be able to travel 35kph at 85% of threshold (300W). It will take a 60kg rider almost the same 300W to travel 35kph on the flats while riding closer to their threshold. Power to weight does not predict flat performance! Heavier riders can carry more speed at a lower percentage of threshold, reinforcing the importance of absolute power over relative power to weight.
Athletes should prioritize watts before weight. Other factors such as repeatability, fatigue resistance, training volume and recovery all take priority over weight. When proper training, recovery and nutrition are exercised, body composition will come as a side effect.
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