Imagine stepping into a world where lasers, bubbles, and even bats play a role in pushing the boundaries of cycling performance. That’s exactly where I found myself one day, inside an abandoned railway tunnel in the heart of Northamptonshire, England. But here’s where it gets controversial: could this hidden testing ground be the secret weapon for teams like Red Bull-Bora-hansgrohe to gain an edge in the highly competitive world of professional cycling? Let’s dive in.
As I arrived, flustered and late, a man in a hi-vis vest greeted me with an unexpected question: ‘Have you had the laser safety briefing?’ I thought I’d misheard, but no—this was no ordinary visit. He led me into an office, handed me a document encased in plastic, and pointed out the stark red warning symbols. The laser I was about to encounter was a ‘level four,’ and without the tinted, wraparound glasses now in my hands, looking at it could be dangerous. And this is the part most people miss: this wasn’t just any laser; it was part of a cutting-edge testing process that could revolutionize how cyclists optimize their performance.
The Catesby Tunnel, a 2.7km-long stretch of abandoned railway buried beneath the Northamptonshire countryside, has been repurposed into a state-of-the-art aero testing facility. Built in 1897 and abandoned in the 1960s, this tunnel hasn’t seen a train in nearly 60 years. Today, its entrance is a nondescript metal warehouse, accessible through roller shutter doors that belie the advanced technology inside. It’s like walking into the back of a Sainsbury’s supermarket, but instead of groceries, you find a hub of innovation.
Ben Thompson, who works at the tunnel, sensed my eagerness to see the setup. He showed me CCTV footage of a rider’s silhouette moving in the shadows—a spooky sight made even more eerie by the mention of a bat colony at the tunnel’s far end. Bat sightings are rare, and of the 10 people who’ve worked here, only two claim to have seen one. Thompson handed me a hi-vis jacket and reminded me of the tunnel’s conditions: dark, damp, and cold, maintained at a constant 10.5°C. ‘Don’t wander off alone,’ he warned, and I nodded obediently, feeling like a schoolboy.
A small van took me through the tunnel’s portal, and as we rolled into the darkness, I couldn’t help but feel a mix of excitement and trepidation. For years, this tunnel has been a testing ground for high-speed vehicles, with the fastest recorded speed topping 200mph. Its smooth, arrow-straight road and controlled environment make it ideal for precision testing. At the end of the road, I noticed large blue barrels filled with gravel—a safety barricade in case something goes wrong.
But today, the focus wasn’t on cars; it was on Dan Bigham, a former motorsport engineer turned Olympic silver medallist, and his team from Red Bull-Bora-hansgrohe. They were measuring real-life computational fluid dynamics (CFD), a digital method for tracking airflow over an object—in this case, a rider and their bike. To do this, they used particle imaging velocimetry (PIV), projecting a laser onto a screen of bubbles and capturing their movement with eight cameras as Bigham rode through them. The goal? To compare these real-world findings with digital models, refining their CFD calculations for greater accuracy. ‘We’re sharpening our tools,’ Bigham explained, which will allow the team to conduct precise CFD tests on riders throughout the season without their physical presence.
Here’s the bold part: while wind tunnels and velodromes are standard for aerodynamic testing, Bigham sees the Catesby Tunnel as a unique tool that blends realism and precision. ‘CFD is an arbitrary environment—it’s maths and a computer,’ he said. ‘What this enables us to do is get that correlation, which hasn’t really been done in cycling before.’ The tunnel allows riders to move naturally while controlling variables like road surface, gradient, and yaw angle. Plus, its enclosed space eliminates crosswinds, making it ideal for repeat testing.
The bubbles themselves are a marvel: filled with helium, coated in a soapy film, and released from 12 ‘free-standing wings’ to form perfectly uniform 0.3mm spheres. Their movement is tracked with precision akin to Hollywood motion tracking, but with hundreds of thousands more data points. The setup is expensive, with around 25 litres of industrial bubble fluid used—a testament to the team’s commitment to accuracy.
But why go to such lengths? Bigham explains it’s about finding the right balance between realism and measurement precision. Field testing offers real-world conditions but lacks precision, while CFD provides precise measurements but is entirely digital. The Catesby Tunnel sits at the sweet spot of this spectrum, offering both realism and control. ‘It’s a bit contrived,’ Bigham admitted, ‘but that’s what makes it perfect for this type of testing.’
As Bigham completed his 100 test runs, dressed in a skinsuit and wearing welder’s goggles that made him look like an insect, I marveled at the effort involved. The chalk spray he used to make surfaces non-reflective—a crucial step for accurate data capture—left him and his bike covered in black. ‘If you take a picture of a car, you see yourself in the reflection, right?’ explained Specialized aerodynamicist Lionello Bardina. ‘We don’t want reflections; we want the true data.’
After six hours in the tunnel, I emerged craving natural light. A month later, Bigham confirmed the testing had correlated with their calculations, though the finer details would take months to analyze. The pursuit of performance doesn’t stop, though. Red Bull-Bora-hansgrohe will continue testing, fine-tuning rider positions, and pushing boundaries.
Here’s the thought-provoking question: as cycling teams increasingly rely on technology like CFD, will riders become harder to convince to participate in physical testing? Bigham noted that riders prefer altitude camps and training over wind tunnels. ‘CFD is powerful, but we need absolute trust in it first,’ he said. The laser test in Catesby was a big step toward building that trust.
As I reflect on my day of lasers, bubbles, and bats, I can’t help but wonder: what other hidden testing grounds are out there, waiting to be discovered? And when they are, will Bigham be the first to find them? One thing’s for sure: I’ll be ready for the safety briefing.
