Since the Tour de France is spending this weekend in the Alps, this is a good time to revisit the idea of power-to-weight ratio, or PWR. In simple terms PWR is a way of comparing two riders of different weights to predict which one has the potential to go uphill faster. When the pitches get steep and the mountain passes get long, the riders with higher PWR values have a big advantage. Here’s what you need to know about this critical performance marker:
Larger riders have more muscle and can generate higher absolute power outputs, but they have more mass to drag uphill. Smaller riders have less mass to accelerate against gravity, but carrying less muscle also means lower absolute power outputs. Riders who excel on the toughest climbs are small, lightweight riders who have high power outputs. But it’s important to remember that PWR isn’t a static number. Rather, it’s a number that corresponds with a specific time. For instance, 5.5 watts/kg for 30 minutes. For 60 minutes that same rider would average lower, like 5.0 watts/kg; and average higher, maybe 6.0 watts/kg, for 15 minutes. To determine a rider’s PWR over a specific duration, you divide the rider’s weight in kilograms into the average power from the effort. Example: Rider A weighs 76 kg and averaged 275 watts for a 20-minute climb, so his PWR for 20 minutes is 3.6 watts/kg. Rider B weighs 55kg and averaged 210 watts for the 20-minute climb and has a PWR of 3.8 watts/kg. Despite producing far less power, the 55-kg rider would be further up the climb after 20 minutes. Or put another way, Rider B should be able to drop Rider A.
Is lighter always better?
This is a common question related to climbing. Generally speaking lighter is better, but an athlete can be too light. You’re not likely to see this at the Tour de France because the riders have a great understanding of their optimal race weights, but in the amateur ranks we do see riders who obsess about weight loss until they become so light they actually harm their performance. Extremely light athletes struggle to maintain consistent high-quality training and are more susceptible to illness, often because they’re not providing their bodies with enough energy to support their immune system and recover from their efforts. When you catch the situation early, a rider can often return to optimal performance by regaining as little as 1-2 kilograms.
Does the weight of the bike get factored in?
Not typically, because at the pro level the assumption is that the bikes weigh the UCI limit of 6.8 kilograms. In principle cutting weight on the bike will effectively increase your PWR, but the danger with factoring bike weight into your numbers is that it provides athletes with a way to “buy” their way to their goal PWR. That means they often stop working to optimize power output and bodyweight. For most people it’s better to maximize PWR regardless of the bike, and then consider weight-savings on the bike as an added race-day advantage.
Does PWR change throughout the year?
Yes, and that’s perfectly normal. Elite racers aim to be as strong as possible when they are also as light as they can be, but this is a delicate balance that can’t be maintained for very long. Nonetheless, throughout the year they try to keep fluctuations in either bodyweight or power output relatively small because gaining weight or losing power means a lot of work to get back to your peak. Experienced amateur cyclists can expect to see a 15% change from the lowest to highest PWR they see during the year, and pros aim for a smaller fluctuation.
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Which is more important, losing weight or gaining power?
For novice cyclists and experienced riders who are carrying around more than 10 extra pounds, losing weight and gaining power are equally important and equally achievable. This also means that heavier cyclists can make bigger improvements in their PWR because they have more room to attack both parts of the equation.
Let’s use a local Colorado Springs climb as an example. Cheyenne Canyon is a 5-kilometer climb with an average 8% grade. Our example rider weighs 75kg with a max sustainable power of 250 watts. Dropping 2.5 kilograms (roughly 5 pounds) with a power output of 250 watts would cut 38 seconds off this rider’s time. Improving power output by 10 watts without any weight loss cuts 41 seconds off his time. This increases to 85 seconds if you improve power output by 20 watts. When you combine losing 2.5 kilograms of bodyweight with a 20-watt increase in sustainable power (both of which are attainable for most cyclists), this rider would go 2:03 faster up Cheyenne Canyon.
Riders at the Tour de France have pretty much maxed out both sides of the PWR equation and they are just about as lean and as powerful as possible. On major climbs, though, that’s why other factors like hydration status, core temperature regulation, and even positioning in the group make such a difference. If a rider can stay cool, stay hydrated, and avoid unnecessary accelerations then he may have more power in reserve to take advantage of his PWR at a crucial time.
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Does PWR stay constant during the Tour de France?
No. Remember, PWR is not a static number. It depends on the duration of the climb, how many hours of racing have been done before that specific climb, how aggressively a particular stage or climb is contested, wind direction, temperature, and even humidity. As riders get tired, overheated/chilled, or dehydrated, PWR goes down. A climb with moderate temperatures, a tailwind and really aggressive racing can result in high PWR values. By the final climbs of long stages and the last mountain stages of the race, even the leaders’ PWRs can drop to around 5 watts/kilogram. In early mountain stages – or for shorter periods within later climbs – they will be around 6 watts/kg.
Where does PWR make the biggest difference?
Power to weight ratio makes a difference anytime you have to accelerate, which is why even large sprinters like Marcel Kittle and Andre Greipel try to stay lean, too. For the climbers and yellow jersey contenders, PWR is most crucial at the steepest parts of big climbs. When the grade is steep, having a higher PWR gives you the ability to accelerate more sharply, which means it provides the opportunity to launch scorching attacks. Riders with lower PWR values can’t accelerate as quickly, but may be able to reel you back in when the climb is less severe.
Enjoy the Tour!
CEO/Head Coach of CTS