Suit seams affect speed

By Idun Haugan

Published 16.03.15

When racers are chasing hundredths of seconds, the difference between winning and losing is tiny. The type of fabric and seam locations can determine whether a cyclist makes it onto the podium or not

When pro cyclists maintain a gruelling pace mile after mile, they do whatever they can to eliminate as much air resistance as possible. That includes shaving their legs so that body hair won’t create drag. And it also means they want state-of-the-art design that can create bike suits that give the best effect and minimal resistance.

The suits of Norway’s national team riders fit like a second layer of skin. The suit weighs almost nothing and the quality of the fabric allows it to breathe. Fabric quality and design are researched over many years and continually improved. That’s why Live Spurkland is conducting test trials in the university’s wind tunnel.

She is a master’s student in the Department of Energy and Process Engineering at NTNU, and her interest in bike suits comes from being an active cyclist herself.



Testing different types of fabric

“I started by testing almost 30 different fabrics on cylinders of various sizes to identify the fabrics’ properties. Based on the results of these initial tests, I had three outfits sewn, each with a slightly different material. Now I’m testing these against the original suit that our national bike team racers use,” says Spurkland.

Cycling outfits must be completely form-fitting, but that does not necessarily mean that the material should be completely smooth. The suits that Spurkland has brought to test have inset pieces of fabric of varied types or surface textures.

“To achieve minimum air resistance, fabric texture has to conform to body shape and the speed of air flow around a given part of the body. By putting together a bike suit using several different materials with varying textures, you can to some extent affect how air flows around the rider.”

When hundredths count

It’s time for the redesigned suits to be put to the test in the wind tunnel – this time on a real person – and professional cyclist and former NTNU student Ingrid Lorvik has made herself available. The national team cyclist is accustomed to long daily training rides, so the session in the wind tunnel is like a tiny warm-up. Spurkland still has a small stock of chocolate and nuts available to keep Lorvik’s energy up, because the headwind in the tunnel is pretty strong when the airflow is turned on.

“It’s important that the suits have as ergonomic a fit as possible,” Lorvik says. “Racers notice immediately when air gets between the suit and the body. The suit has to fit as if it’s glued on. And when we ride in southern Europe where it’s really hot, it’s more comfortable to have a mesh inset in some places for better ventilation.”

“The suit details don’t matter as much for the recreational rider, but for competitors they’re critical,” she says. “There’s also a psychological element in knowing that you have the best possible gear. What goes on in your head is so important when you’re giving your last ounce of strength in a race.”

Powerful headwind

Spurkland has programmed different variables she wants to measure into a computer connected to the wind tunnel. The bike used in the test is fastened to a weight that measures aerodynamic drag. Pressure and temperature parameters have also been entered into the program.

During the testing, Spurkland’s program records many measurement sequences of 30 seconds each. Half of them are dynamic, where the cyclist pedals at a constant cadence. The other half are static, where the rider sits perfectly still in one position. In all of the trials the headwinds in the tunnel are rather brisk, with speeds varying from 35 to 65 km/h.

On track to an improved uniform

When Spurkland analyses the data after the testing, she pulls out some of the results:

NTNU's wind tunnels • The Aerodynamic Laboratory at NTNU has four wind tunnels. The one used for bike suit testing is the biggest, and is also the largest in Norway.

• The big tunnel is 12 meters long, 3 meters wide and 1.8 meters high. It is connected to a massive turbine that sends wind into the tunnel.

• Wind speeds can reach as high as 100 km/h.

• The wind tunnel is used to test the efficiency of wind turbines, the stability of offshore construction and the speed of athletes in various sports.

• The Norwegian organization Olympiatoppen, which is responsible for developing top athletes in Norway, has run experiments and tests in the tunnel since the early 1990s.

• Suits for various sports have been improved by testing in the tunnel. Most experiments are done with test dummies, not real athletes.

• Many Norwegian athletes have also used the wind tunnel to train and test different positions, particularly for downhill skiing, ski jumping and skating.

“It appears that the modified material on the arms and shoulders can have a positive effect. The tights with a non-traditional fabric came out best in the first test, so it will be exciting to work more with that material. I have some more tests to do before I can draw any final conclusions.”

The next step is to get a new test suit made with adjustments based on the trial results in the wind tunnel. The Norwegian company Trimtex is contracted to create the test suits for Spurkland’s work.

“One of the suit changes will be in the placement of seams on the jersey so that they’re more aligned with the travel direction. We’ve also changed the sleeve length and placement of pockets slightly. We want to test how much extra fabric structure at the bottom of the shorts and sleeves affects performance. A new test round for this suit version will use both a live cyclist and a test dummy, at speeds from 35 to 75 km/h,” says Spurkland.

Gaining hundredths of seconds doesn’t happen all at once. But if Spurkland’s tests show good results, pro cyclists can eventually compete in new and improved suits. Which can give them that tiny extra edge.

Testing cycling uniforms in NTNU’s wind tunnel: