The power meter era of cycling has brought with it a whole new training vocabulary. Where we once compared rides by average speed, time, or heart rate, now we talk about watts and functional threshold power (FTP).

As training with power has evolved, we’ve added even more ways to measure strength and performance. One of the most insightful metrics is power-to-weight ratio, expressed as watts per kilogram (W/kg). If you ride on Zwift or follow pro racing, you’ve probably heard riders talk about watts per kilo. But what does it actually mean — and more importantly, what does your W/kg say about you?

What Is Power-to-Weight Ratio?

A cyclist’s power-to-weight ratio is expressed in watts per kilogram (W/kg).

Power is how hard you push the pedals, measured in watts. Weight is your body mass, measured in kilograms. Power-to-weight ratio simply divides the two.

Example: A rider producing 250 watts who weighs 70 kg has a power-to-weight ratio of: 250 ÷ 70 = 3.6 W/kg

Because it’s a ratio, different riders can produce radically different watts at the pedals yet have the same W/kg.

For example, a 50 kg rider putting down 150 watts has a 3.0 W/kg ratio. But a 100 kg rider would need to throw down 300 watts to have the same 3.0 W/kg ratio.

The advent of power meters brought W/kg to the fore for high-level training and racing. But it was the indoor training platform Zwift — which always displays a rider’s current W/kg and uses the metric to divide ability levels for competitions and group rides — that arguably introduced the topic to a wider cycling audience.

As is likely obvious, the higher a rider’s W/kg, the stronger and faster they are.

At its core, W/kg reflects a basic physics principle: how much power is available to move each kilogram of mass against gravity.

Power-to-Weight Ratio Versus Functional Threshold Power

A rider’s Power-to-Weight Ratio (W/kg) and Functional Threshold Power (FTP) are distinct but related, as both involve power. FTP doesn’t have a weight component, but it does have a time component. FTP is generally defined as the maximum average power a rider can sustain for one hour.

(Note: Although FTP refers to one hour power, it is often estimated from a 20-minute test.)

So, your FTP is simply a number like 250 watts.

Two riders may have the same FTP of 250 watts, but the lighter rider will have a higher W/kg.

250 watts ÷ 50 kilograms = 5.0 W/kg
250 watts ÷ 100 kilograms = 2.5 W/kg

While FTP typically refers to roughly one-hour power, W/kg is analyzed over multiple time spans, from a few seconds to over an hour.

One reason W/kg is analyzed over multiple time spans — and why it’s becoming increasingly discussed, to the point of supplanting FTP as a primary performance metric in some situations — is that one-hour power is not every rider’s strength, and not all climbs are an hour long.

Some riders can put down mind-blowing 1-, 5-, 10-, or 20-minute power, which can absolutely make the difference in a race, even if their one-hour power is more pedestrian.

This is why modern training software often displays a rider’s “power curve,” showing their best W/kg across durations from seconds to hours.

Where Power-to-Weight Ratio Matters Most

“The steeper it gets, the more having a higher w/kg matters.”

Power-to-weight ratio is most insightful for predicting climbing performance. Once gravity becomes the primary force acting on the rider, W/kg becomes the dominant factor. “The steeper it gets, the more having a higher w/kg matters,” Cody Stephenson, education manager at TrainingPeaks, explains.

And the higher a rider’s W/kg, the faster they will climb — all else equal.

Absolute watts matter less than many riders expect on climbs. One rider could put down twice as much power as the rider next to them, but if the two riders are riding at the same W/kg, they will likely be climbing at about the same speed.

Does W/kg Matter on Flat Roads?

While a higher W/kg can be the great equalizer for lighter and less powerful riders on the climbs, it’s not the same story on flat roads. With gravity largely removed from the equation, the rider who can throw down the most pure watts is usually fastest. That’s why big and powerful riders can thrive on flat roads even while they suffer on the climbs.

However, this is with all else equal. On flat roads and at faster speeds, aerodynamics are the biggest factor.

Larger riders often experience more drag simply because they have more surface area. There’s also the aerodynamic profile of the bike, the rider’s apparel, and the rider’s position.

And don’t forget rolling resistance and drivetrain friction.

Having a great power-to-weight ratio never hurts. But even if you can sustain an impressive 4.0 W/kg on the climbs, you still may find it hard to stay on the wheel of the big dude with the spare tyre around his belly who can throw down 350 watts for km after km on the flats.

What W/kg Doesn’t Tell You

There are several important caveats to understand when considering W/kg.

One of the most significant: W/kg typically accounts only for the rider’s weight, not their equipment. But on the road, what really matters is total system weight — rider plus bike.

So, if you’re climbing at the same W/kg as another rider, but you’re on a significantly lighter bike, you’ll have the advantage. This is why climbers obsess about bike weight.

W/kg doesn’t consider frictional losses (drivetrain or tires). No matter your W/kg, a big improvement in rolling resistance or drivetrain friction will help you climb faster, while slow-rolling tyres and a grinding drivetrain will slow you down even if you have a sparkling W/kg.

Aerodynamics is another area not considered by W/kg.

And the fact is, the greater the W/kg you can sustain, the faster you will go uphill. And the faster you go, even on the climbs, the more aerodynamics matter.

This leads us into the murky world of the “tipping point.”

This is typically defined as the grade or steepness of the hill where weight — and therefore W/kg — becomes more important than aerodynamics.

“The transition is probably somewhere around a 3–6 percent grade. Once you get above that, a lighter rider with a higher w/kg is going to be at an advantage, but in flatter, high-speed or high-headwind situations, a bigger rider with higher raw power will still beat a small rider with better power to weight. Understanding this can help an athlete target their races and refine their tactics and training,” Stephenson explains.

If your sustainable W/kg is on the lower end, your tipping point may be at a shallower grade. But for the fastest climbers, the tipping point is a steeper grade simply because they are going so fast up the hill.

This is why riders like Tadej Pogačar increasingly choose their most aerodynamic racing bike even on the biggest climbing stages of the Tour de France.

But note that the pros’ bikes have a minimum weight of 6.8 kg, which, in the modern era, is achievable even with the latest generation of aero bikes like Colnago’s Y1Rs.

If the UCI lowered its weight minimum, you might see the return of climbing bikes for the toughest stages.

The Danger of Watts Per Kilogram Obsession

There’s no doubt that improving your watts per kilogram will help you ride up the toughest climbs faster.

The problem is that focusing on W/kg can cause cyclists to obsess over their weight, and sometimes to an unhealthy degree.

A healthy weight is great; being underweight while placing heavy athletic demands on your body will cause illness and break your body down.

Pro cycling — like many endurance sports — has a weight problem. It has gotten better in recent years simply because some have finally admitted there is a problem and begun talking about it. But much still needs to be done to improve the overall health and sustainability of athletes in both the men’s and women’s peloton.

The focus should never be on being as light as possible at all costs.

Health and longevity should be the focus. An ideal weight allows you to train hard, ride hard, enjoy the ride, and stay healthy.

Rides are Usually More Than Just a Climb

Another thing to consider is that climbs are typically only one part of the ride. There’s usually riding before and after the climb. So don’t just think of how to get from the bottom of the climb to the top as fast as possible — focus on the whole ride.

Choosing the lightest possible bike may get you to the top of the climb faster, but you still need to reach the base and manage the descent that follows.

This is why a heavier but more aerodynamic bike (plus optimising rolling resistance, drivetrain losses, rider position, etc.) is often faster overall from A to B, even if it’s a bit slower on the climbs.

How Do You Boost Your W/kg?

The answer is in the equation. The power-to-weight ratio has two parts: power and weight.

As Stephenson explains, you improve the ratio by decreasing weight, increasing power, or both.

“If a 91kg rider gains 40 watts from 250 to 290, that’s a pretty good improvement, 2.8 W/kg to 3.2 W/kg, but if that same rider also lost 14kg, they would end up at 4.0 W/kg, and that’s a whole different level, possibly two categories of racing different.”

If you have body weight you can safely and healthily lose, that’s a great place to start. Dieting and weight loss are also likely to be your least expensive path to an improved W/kg.

“If an athlete is overweight, especially if their excess weight is fat instead of muscle, targeting that will make the biggest, fastest difference. This will involve similar training, but maybe more focus on nutrition to lose weight at the same time,” Stephenson says.

Then there’s your power.

“If your body composition is good and in an athletic range, it will just take the long, hard work of improving your aerobic fitness and threshold power,” Stephenson explains.

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