Power-to-Weight Ratio: Why it’s So Important in Cycling
By Hunter Allen, PCG Founder/CEO and Master Coach
Your body weight and bike weight have a lot to do with how many watts you produce and how fast you can ride your bicycle. A heavier rider will be able to (and will have to) produce more watts than a lighter rider going the same speed up a hill. In the most famous bicycle race of them all, the Tour de France, power-to-weight ratio (w/kg, watts per kilogram) is probably one of the most important factors of success. You still have to time trial in many races, including the Tour, so the power-to-CdA (coefficient of drag) ratio is also important, but still not as important as power-to-weight when you look at the overall picture.
It’s not just for the Tour that power-to-weight is important; it’s also important in your local group rides or races and even just fun competitive rides with your friends. If your friend weighs 15 pounds less than you and can produce the same watts at threshold, he’s going to beat you every time. Since many rides and races have hills in them and more often than not a hill can be the determining factor in a fast group ride or race, many riders want to know how they can improve their power-to-weight ratio. What can you do that will help you go faster up a hill, maintain a healthy body, and continue to produce strong numbers on the flats?
To answer that question, let’s first examine what a difference 10 pounds lighter weight might do for you. For example, let’s say you weigh 165 pounds and can produce 280 watts at your functional threshold power. Since the ratio is in kilograms, we have to start by converting your weight into kilograms: 165 divided by 2.2 equals 75 kilos. 280 watts divided by 75 kilos equals 3.73 w/kg. If we examine the power profiling chart in TrainingPeaks WKO+ software, this puts you right at the top of the Category 4 range for your functional threshold power. Now let’s say you lose 10 pounds of body weight. Where would this put you on the power profile chart? 155 divided by 2.2 equals 70.45 kilos, and now your w/kg is 3.97, right on the edge of being a solid Category 3 racer. This means that without any additional improvements in your threshold power, you can easily up your category. This could certainly be the difference between winning a race and being pack filler.
Now that we know how much a 10-pound weight loss could impact your level of racing, imagine what would happen if you not only lost the 10 pounds but also improved your functional threshold power to 300 watts. All of a sudden you’re now at 4.25 w/kg, which is knocking on the door of Category 2! Knock off 2 pounds more by reducing the weight of your bike, and now you’re a solid Category 2 racer.
With some body fat loss, a bit of strategic weight reduction on the bike, and solid training, it’s not hard to get from Category 4 to Category 2. Of course it’s not quite that simple (you still have to win races), but it does prove a point about how important weight is in this sport.
The next question is, of course, how much weight you can lose and how much weight you should lose. Going overboard you can compromise your immune system and reduce muscle mass, which could cause a subsequent reduction in power output. Like other things in life, it’s a balance, and you have to balance the performance gains with your health.
There’s a difference between health and fitness; all you have to do is look at the riders in the Tour to see that they are fit but probably not as healthy. Extreme endurance events aren’t the healthiest thing you can do to your body, and as a consequence muscle mass is compromised, along with your immune system and short-term health. The same thing happens to a rider who cuts his body fat down too much. Many cyclists are naturally at 5-8% body fat, but some go even lower. If you drop below 5%, you really need to be careful. Performance won’t be optimal if you cut below your optimal weight; your power output will be reduced, and the weight loss performance gains could be negated by your reduction in power output. Use a power meter and track your weight on a daily basis to see if your overall w/kg ratio has gone down with your weight loss.
The chart below shows the relationship between your absolute average power and your power-to-weight ratio. Notice that the green bar (average power) and the blue bar (w/kg) are relatively close together. As the month goes on, they get farther and farther apart, with the blue bar (w/kg) growing much taller in relationship to the green bar (average power). This is exactly what you want. Your w/kg should increase in relation to your average power, showing that your overall performance has improved, either from weight loss or a higher functional threshold power. If you see the opposite (the blue bar dropping in relation to the green bar), either you are losing fitness or you have lost too much weight and are now losing power, as well.
One of the easiest things to do to improve your power-to-weight ratio is to cut weight. While fitness improvements sometimes give you more emotional bang for your buck, losing weight doesn’t take as long, and if you do it in a relatively slow manner (1 pound a week), you’ll be less likely to lose muscle mass. One of the keys I’ve found to losing weight gradually and maintaining your energy levels is to go to bed just a little hungry each night. Not starving, mind you, but a little bit hungry. This ensures that you’re under-feeding yourself slightly and encouraging your body to utilize fat stores while you sleep. This is a great way to lose body fat slowly and keep your immune system in check.
Power-to-weight ratio is an important component to success in cycling. Maintaining your health while making sure you have the best power-to-weight ratio possible is not easy. Take it slow and make sure you continue to train smart while decreasing your body fat, and at the same time see if you can shed some weight from your bike, as well. It’s not likely that a few pounds will make much difference in your performance, so if you have 1-2 pounds to lose and are wondering if you should try it, it’s best to play it safe and just not worry about it. However, it’s possible that with more than a few pounds of weight reduction, you could be the one at the top of the hill in the front group instead of near mid pack.