For the likes of us, helmet-wearing amateurs in normal clothes, there’s a 60mph limit in the tunnel. Other users – properly kitted BTCC teams, Le Mans racers – are allowed much higher speeds, although the tunnel’s operators reserve the right to run risk assessments and frame different rules for different users.
It’s an eerie experience, driving the tunnel, with the lights arching over your head and all the car’s noise reflected faithfully back from the domed roof. There’s an echo too. Even a mile a minute feels fast at first.
I found myself wondering what it would be like at 150mph in an LMP1 car. On the other hand, the road is wide, an Atom 4 is ultra-stable and, of course, it accelerates like a rocket. Even though Prior and I may have strayed a smidgen further up the speed range than 60mph (who could resist?), it was still easy to do three runs in each direction, northerly at first towards a driver-operated turntable (essential, I would imagine, for big-bodied LM cars) and then southwards and back to the start.
Beyond the northerly turntable, we were told, was 60m of bat colony, its existence a condition of the aero tunnel’s planning approval. According to Roberts, the bats are impervious to sound, even LMP1 cars at full noise, as long as they are undisturbed in other ways.
Interpretation of the results – beyond the surprising protective qualities of the screen – took a while, but they were fascinating. “Our tests showed that the screen generates 100 Newtons of downforce, which helps shift the aero balance to the centre of the car. It reduces buffeting and directs air into the engine’s intake too, and also reduces drag. So we’ve had a win-win-win,” says Saunders.
“This fine level of testing wouldn’t be possible for us outside the tunnel. Improvements like this are repeated all over the car, and together they make a very direct and noticeable change improvement for occupants. So it has all been very well worthwhile.”