Tall vs small: how much difference does body size make when cycling?

Whether you’re taller or shorter, it’s hard to know if your height is helping or hindering you out on the road. Looking at the pro peloton, we can spot a few trends: the climbers are usually smaller and lighter, and the time triallists are usually taller and heavier. Ultimately, the performance difference between smaller and bigger riders is about the complicated relationship between size, weight and power that scientists refer to as allometric scaling.

We’ve done our best to make that complicated relationship as simple as possible, so you can understand why you’re going faster or slower than your riding mates. Plus, we’ve done some real-world ‘tall vs short’ testing to show what all that science means out on the road. Together, you should get a pretty clear idea of where your height is an advantage, and where it may be a disadvantage.

Climbing

On a climb, most of the resistance is from gravity, so performance is all about watts per kilo. That is, the amount of power you can put out for every kilogram of body weight. When climbing, two cyclists riding at the same watts per kilo on equivalent equipment will go at the same speed, even if they weigh different amounts.

A taller rider will naturally be heavier than a smaller rider, even if they both have the same BMI and physique. That means that a taller, heavier rider has to produce a higher wattage to get an equivalent watts per kilo to a smaller, lighter rider.

The issue for taller riders is that those extra inches of height don’t lead to an equivalent increase in power. Taller riders might be 10% heavier than their smaller counterparts, but they’re not 10% more powerful. Some of that extra weight will be muscle, but a lot of it will be all the other stuff that makes up our bodies, like bones, organs and fat. That means that on a climb, a taller, heavier rider will struggle to match the watts per kilo of a smaller rider.

This change in efficiency is due to allometric scaling, a system that models how an organism changes as it changes in size. The equation is Y= aM^b, where Y is biological variable, M is body mass and b is the scaling exponent. For climbing, the scaling exponent is taken as 0.8.

But it’s not as simple as ‘heavier equals harder’. System mass plays a part too. The weight of a rider’s bike, clothing and water bottles will be about 10kg regardless of the rider’s weight. That means that the lighter a rider gets, the heavier their bike gets, proportionally.

Subsequently, the ‘ideal’ weight for a climber is a balance of these two penalties: the weight penalty of the bike, and the efficiency per kilo penalty that comes with extra height. The climbers in the men’s WorldTour average 176cm (5’9”) and 62kg (137lbs), so perhaps that gives us some indication of where the peak of that performance curve lies.

On the flat

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Extra volume increases power more than it increases drag

When riding on flat roads, a rider’s weight only matters when they are accelerating or decelerating. Gravitational pull isn’t a factor. Instead, air resistance is the biggest force that riders have to overcome.

Taller riders are less aerodynamic than smaller riders, as their larger size means that they have a larger frontal area that hits the wind. It might seem natural that taller riders would be slower because of that larger frontal area, but in fact, taller riders are at an advantage on the flat.

It’s all down to the complex relationship between power, weight and size. As the size of a rider increases, their surface area increases as a squared function – to the power of two. But their volume increases as a cubed function – to the power of three.

That means that as a rider’s height increases, their surface area increases, but their volume increases substantially more. All that extra volume means that just a few extra inches in height mean more muscle mass, and a lot more power.

Considering the hunched-over riding position of road cyclists, that surface area increase becomes even less significant. Generally speaking, we’re low down on the bars, with our shoulders taking the majority of the wind. The frontal area of a tall cyclist isn’t miles apart from the frontal area of a small cyclist.

Again, this isn’t a simple linear relationship, and it’s not as simple as saying that a taller rider will always be more powerful or faster. Volume might increase as a cubed function, but power doesn’t, because we’re not 100% efficient. In fact, we get less efficient as we get bigger. For the mathematicians out there, the scaling exponent for this calculation is 0.66. That means that for every kilogram of extra mass a taller rider carries, only two thirds of it will be extra muscle, so while heavier riders are usually stronger, they’re carrying a lot more ‘useless’ weight, as far as cycling is concerned.

In practice

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Taller riders might struggle to draft behind small riders

Okay, so that’s the hypothetical stuff out of the way. Let’s answer the question most of us will be asking: how does a difference in height affect us out on the road?

To find out, we sent GCN presenter Conor Dunne and British rider Max Stedman out on their bikes. Conor was once the tallest rider in the men’s WorldTour, at 204cm (6’ 8”) and 90kg (198lbs). Stedman is among the smallest in the peloton at only 167cm (5’ 5”) and 55kg (121lbs).

The results of the test were a little skewed due to the difference in fitness between the two riders: Stedman was in the form of his life, riding and racing at the top level, whilst Conor is a few years into his retirement, logging more hours each week on the sofa than the saddle. Either way, we got a good sense of how height influences performance out on the roads.

Side-by-side

When riding side-by-side on a flat section, Conor had to produce 32% more power to stay alongside Stedman. To maintain 30kph, Conor had to pedal at 355 watts, whereas Stedman could ride at only 240w. This is because of the increased aerodynamic drag Conor experiences due to his larger size.

Proportionally though, Stedman was pushing harder. For Stedman, who weighs just 55kg, 240w is 4.36 watts per kilo. For Conor, who weighs 90kg, 355w is just 3.94 watts per kilo. Remember that relationship between size, area and volume: Conor’s extra height gives him a greater area than Stedman, but a far greater volume. All that extra volume means Conor is heavier and stronger: in a sprint test, he hit 1300w, whereas Max hit just 980w. Riding along at a constant speed, then, Conor can use that extra power to propel himself more easily, without the extra kilos having a negative effect on his speed.

Drafting

Smaller riders have a harder time on the long, flat sections, but they can go a long way to redressing the balance by drafting behind other riders. Behind tall riders like Conor, the energy savings can be enormous.

Drafting behind Conor at 30kph, Stedman only had to produce 156w to keep up: 35% less than when he was riding in the wind. That’s more than enough to compensate for the increased effort Stedman needs to exert to keep up with tall riders like Conor on flat roads.

For Conor, there was virtually no advantage to drafting behind Stedman. He had to pedal at 353w to keep up with Stedman at 30kph, just 2w less than when riding solo. The headwind probably had something to do with this result, but it’s clear that for a rider of Conor’s stature, a small rider doesn’t offer much protection from the wind.

Climbing

On a climb, it was a completely different story. The pair took on a local climb, and the challenge was simple: Conor was going to stick to Stedman’s wheel for as long as possible. It didn’t take long for Stedman to leave Conor behind, and when we looked at the numbers at the top, it was clear to see why. Stedman had held 430w for the two and a half minute climb, meaning he’d ridden at 7.8 watts per kilo.

For Conor to remain alongside him, he would have had to produce an average of 703w up the climb. That’s a mammoth figure – there are probably only one or two cyclists in the world who would be able to hold wattage like that for over two minutes. Filippo Ganna springs to mind… For most tall cyclists, though, keeping up with a lightweight rider like Stedman on a climb is impossible.

Sprinting

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In a sprint, Stedman pips Conor to the post

We were curious to see who would come out on top in a sprint. In the pro peloton, sprinters tend to be fairly average in height, coming somewhere between the small climbers and tall time triallists. Of course there are exceptions: over the years we’ve seen small riders like Mark Cavendish (175cm) and Caleb Ewan (167cm) winning sprints, and we’ve seen tall riders like André Greipel (183cm) and Mario Cipollini (189cm) do the same. The average height of pro sprinters is 179cm (5’ 10”), giving them a good balance between power and aerodynamics, but which of the two extremes – tall or short – is best in a sprint?

In our test out on the roads, Stedman came out on top for all three types of effort we threw at them. In a standing sprint, or race-simulating ‘cat and mouse’ sprint, Conor couldn’t match Stedman’s snappy acceleration. Even in a rolling sprint, Conor got pipped to the post ever so slightly. This is due to the aerodynamic penalty facing the taller rider. As the speeds increase, that minor aerodynamic disadvantage facing Conor grows and grows, until eventually it outweighs the power advantage he has over Stedman. Subsequently, Conor gets left behind in the sprint.

Size isn't everything

Understanding how your height helps or hinders you out on the road is important, but whatever your height, don’t forget that there are going to be rides and routes that suit you, and others that don’t. Despite what we’ve covered today, there’s no need to pigeonhole yourself based on your size. There are loads of pro cyclists that excel in specialisms that they ‘shouldn’t’, based on their height, so don’t write off a certain type of riding because you’re taller or shorter than most of the people who do it, especially if your main focus is enjoyment rather than winning races.