Sound of the Underground: welcome to Top Gear Tunnel Run

Which means you wouldn’t know what a Group B Rally car, screaming V12 track-only hypercar, twin-supercharged vintage Formula One car, a NASCAR racer and many other mad, multi- cylindered machines sound like at flat chat through an incredibly confined space. And – trust me – that’s worth a watch. And possibly a new pair of headphones.

But it was all made possible because of one mind-blowing location: a really, really long (we’re talking nearly two miles), really, really dark and frightfully eerie railway tunnel buried deep in the heart of Northamptonshire. And at this point, we need to rewind back to old Henry Attenborough, and a time when people used to ride penny farthings and put children up chimneys.

Photography: Mark Riccioni

See, back in the 19th century, Henry was the owner of the Catesby estate. And when these newfangled things called ‘trains’ came along, he objected to the “unsightly” chuffing steam machines as they spoiled the view from his stately home. So, he decided to bury them.

Taking the old adage of “out of sight, out of mind” to a whole new level, in 1895, Henry demanded that 230,000m3 of hillside was bored out of his land, so 30 million blue-hued bricks could be laid – by hand – in order to construct a perfectly straight 2,700m long tunnel. Catesby tunnel.

For nearly 70 years, trains ran through Catesby tunnel, connecting the industrial powerhouses of Manchester and Sheffield to the heart of London. But it was abandoned in 1966, falling silent for over half a century, until recently, when it got a multimillion-pound makeover.

What kind of makeover? Well, you’re probably familiar with the concept of wind tunnels. They have become vital tools for the development of both racecars and road cars – either to make cars more slippery or sticky through air management. Traditionally, they work by air being sucked or blown over a static car (or even a scale model on an artificial rolling road) so people in oversized lab coats can scratch their oversized foreheads and take measurements about aero efficiency.

Unsurprisingly, wind tunnels are hugely expensive to both build and operate. But there’s a simpler solution: flipping that whole idea on its head. That’s what the CFD and aero guru TotalSim (the force behind Catesby’s transformation and the majority stakeholder) has done.

Inspired by Chip Ganassi Racing (the US race team that competes in IndyCar and NASCAR) that converted Laurel Hill tunnel in Pennsylvania for aerodynamic testing back in 2004, the team at TotalSim thought it would do the same in the UK.

So it bought Catesby, cleared mountains of aged pigeon poo, drained the flood water, strip lit one side (which is easier on drivers’ peripheral vision at high speeds), lined the roof (to help reduce drips from the damp brickwork and 70 years of soot), and poured two miles of tarmac in one continuous flow, with no joins, using the same people who just resurfaced Silverstone to make the perfect road. One that’s completely flat, with no bump bigger than half a millimetre.

Thanks to TotalSim, Catesby tunnel is now the ultimate wind tunnel... because it’s not a wind tunnel. It’s just a sealed off hole with a turntable at each end so cars can run constantly and confidentially. There’s no wind, no rain, no weather... at all. Just a constant 10°C, day or night. Perfect conditions for 24/7 testing as things are a lot more consistent, accurate and reliable. It’s already forged a reputation as a world class, state of the art, subterranean test centre, used by carmakers and racing teams from around the world to develop everything from aero to acoustics.

However there are significant differences between Chip Ganassi’s Laurel Hill tunnel and Catesby. First, at 2,740m Catesby is twice as long. To give you a sense of scale, a car can travel at 100mph for 40 seconds through it. And while Lauren Hill is a private test facility, anyone can book Catesby. This got us thinking... how fast can you go down it? How much noise can you make? And has anyone seen the corporate credit card?

“Anything is possible as long as there’s a suitable risk assessment in place,” the email from the people at Catesby read. That’s when our minds really started frothing as there’s no better feeling than cracking a window, dropping a few gears and blasting through a tunnel. But being buried some nine metres below the surface and with no speed cameras, Catesby is the ultimate extension of that idea because you can make as much noise and go as fast as you like.

With this info, we hit the phones to gather a band of rockstar cars that go all the way up to 11. Because as sensible, silent EVs take over, the future of cars might be AC/DC... but it’s hardly rock and roll. Whereas an Aston Martin Valkyrie AMR PRO, Lambo Huracán STO, Audi Group B S1 E2, NASCAR Dodge, Merc S600 (that sounds like a V12 F1 car), Caterham 620R and BRM V16 are noisy. Really noisy.

They’re also rather fast and quite a handful. Especially in the dark. Getting a driver for the new YouTube series was the simplest part of many complicated logistics. That’s because The Stig isn’t affected by low light, isn’t fazed by speed and has no eardrums to perforate.

Best of all, we wanted to put you in the passenger seat, so we got some fancy tech to create the most engaging video experience possible. And that’s thanks to Mike, the anthropomorphous binaural mic.

Inside Mike’s ears are two receivers, which record sound just like our human ears... in 3D. And he’s shaped like a head to mimic how sound travels into and around our heads. So, when you play it back, you hear what Mike hears. As if you’re actually there, listening with your very own lugholes. It isn’t just surround sound, it’s sonic sorcery.

Now imagine what it sounds like when we put Mike in the passenger seat, to bring that tunnel run magic straight into your ears. Well, that’s what we’ve done. It’s the sound of the underground. And it’s going to get loud. So clean your ears out, subscribe to the TG YouTube channel and keep an eye out for Top Gear Tunnel Run.