Testing Aerodynamics In The Wind Tunnel With The Rally Cycling Pro Team

March 11, 2021

Testing Aerodynamics In The Wind Tunnel With The Rally Cycling Pro Team

[This article originally appeared on Rally Cycling's website. We extend our thanks to the team for allowing us to share it with you here. (Photos: Steven Schwartz)]

Magnus Sheffield is one of the most exciting prospects in American bike racing, with a junior world record in the pursuit and a podium in the junior road race at the 2019 World Championships to his name. To prepare for this first season racing professionally on the road, Rally Cycling sent Sheffield to work on his form in the A2 Wind Tunnel in North Carolina, with the assistance of bike fitting specialist Paraic McGlynn.

“The unique thing about the wind tunnel is that it doesn’t matter what you look like, it doesn’t care what color jersey you’re wearing, it doesn’t matter about any of those details, it’s purely science, and what is fastest,” Sheffield explained.

It’s not like simply hopping onto an indoor trainer and pedaling, either. An incredible amount of self-control is required.

“When I’m doing a run in the wind tunnel, I’m not actually an athlete, I become a mannequin. And that’s because you’re trying to be as still as possible, any kind of movement that isn’t necessary can throw the numbers off.”

cyclist in wind tunnel

Even tiny, often subconscious movements can put the whole thing out of whack.

“If you slightly move your eyes, that changes your neck, and that changes the head position. It requires a lot of focus and it’s pretty exhausting, trying to be super-still.”

Paraic McGlynn, a twenty-year bike-fitting veteran, explained what it was like to work with Sheffield in the tunnel.

“Magnus is interesting as an athlete. He has great body awareness, he’s finely tuned to what his body is doing. He has very complex mechanics to his fit which means his fit becomes more challenging. His attention to detail means we can accomplish more when we fit him. It affects alignment everywhere.”

pro cyclist wind tunnel

McGlynn also said the fact Sheffield spent so long working in the velodrome for his successful individual pursuit record attempt made it easier to work with him in the tunnel.

“Magnus spent two-and-a-half months riding a TT bike on the track every day to prepare for his world record attempt. As a result of that adaptation time, we can do more with his position.”

It is traditionally considered easier to improve aerodynamics than to increase a rider’s maximum power. And so, fine-tuning the athlete’s position and reducing their drag is the ‘easiest’ route to increased overall speed.

“We are trying to get to him at or beyond his historically low drag. It’s not just about wattage, it’s also about drag,” McGlynn explained. “It depends on distance. The shorter the distance, the higher the speed, the more you’re willing to sacrifice physiology for aerodynamics.”


The level of detail that the wind tunnel allows an athlete to optimize can be a little dizzying. With LEM Helmets joining Rally Cycling as a sponsor this year, a lot of work was done with their TT helmet and working out how best it would perform for Sheffield.

“The biggest thing in the wind tunnel is the head position, and particularly the helmet. We were trying to figure out exactly the best position for it on my head. How high? Do you want it more turned back, more turned forward? A ‘head down’ position is the fastest no matter what, but obviously, you can’t see.”

And so then you get into the trade-offs between what is objectively the fastest, and what position, while slower, allows the rider to actually race their bike.

cycling aerodynamic testing

“We also ran race simulations, so it’s like, ‘Alright, this is the head position I want to be in when I’m going in a straight line, and then this is the head position that I want to be in looking out for a corner, or looking out in front of the road, and then once I see [where I am going], duck down into the faster position again."

And then, of course, there is the suit you wear. Sheffield was impressed with the Pactimo Flyte Suit.

“I had my pursuit world record suit with me, so I brought that, because I knew it was fitted to me and was curious to see how that compared to the team edition Pactimo suit. We also brought some other third-party suits as well to see how they compared.”

The testing couldn’t have gone better.

“The Pactimo suit tested the fastest of them all, which I was quite surprised about because it was just a stock suit, as opposed to one tailored to me. I think now that we have the data and we see how it fits, we can make it even faster because there were some areas that fit looser and tighter. In general, it was a very fast suit.”

McGlynn, an Irishman who worked with Cycling Ireland and is now the founder and chief technologist of Cyclologic, was the person responsible for helping Sheffield get the most out of his time in the tunnel. McGlynn comes from a background of racing himself, before moving into performance.

“I started off as an athlete racing in Ireland in the 1980s, then in the early ‘90s, I had the opportunity to go on a full-time program to study cycling. It became really clear to me that things were done the same way for a while. It struck me that bike fitting was the most important thing, it seemed behind the other areas.”

While we may normally think of bike fitting and aerodynamics as two separate concepts, both impacting on performance in their own way, the truth is that they are often inextricably linked. The real trick, of course, is to balance both; an aerodynamic, fast position that the rider can sustain for a given amount of time and over a variety of terrains. Sheffield was full of Praise for McGlynn’s insight and experience during the process.

“I’m super grateful that Rally Cycling was able to get the opportunity for me to bring in the new bike [to the wind tunnel], and to be able to bring in Paraic. His knowledge is invaluable.

a2 wind tunnel

“It’s like some people say ‘there are a lot of scientists but there’s not a lot of rocket scientists’, those are the ones that are hard to find.”

While it may seem – with all this talk of drag coefficients and world records – like bike fitting is beneficial for only the most elite, but the truth is much different.

“Everyone needs a bike fit,” McGlynn says. “Pain on the bike isn’t usual. A good bike fitter will understand the individual, they’ll check core strength, flexibility. Analysis while on the bike. And then the fourth part, which is most important, take everything they gathered and what they saw on the bike, and figure out a good action plan to help that person ride a bike comfortably and efficiently.”


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