World’s fastest wheels.

(Stefan Marjora

The Hakskeen Pan desert in South Africa is perhaps the emptiest stretch of land on Earth. As far as the eye can see, you will simply find the sun-baked clay, mottled like cracked enamel. But when you are travelling at 1,000mph (1,609km/h), even the clearest terrain presents hidden dangers. “You are travelling faster than a bullet, says Mark Chapman. “So if you go over a stone, it’s like someone shooting at the wheel.”

Building bullet-proof wheels is just one of the many challenges that Chapman has to face as the chief engineer on the Bloodhound Supersonic Car. “These are gonna be the fastest wheels in history,” he says.

Chapman first became involved when he found a mysterious call on his answer machine, asking him to meet in the pub to discuss a “unique vehicle-based project”. It didn’t take many beers for him to agree to take it on. “I saw some early drawings of the car, and the penny dropped pretty quick that this was something very, very special,” he says. “You’d kick yourself if you got this opportunity and you didn’t take it up.” It builds on some of the designs of the Thrust SSC – the previous record holder, which broke the sound barrier at more than 750mph (1207km/h) in 1997. But accelerating beyond that point has presented some unique problems.

At the most basic level, Chapman’s team had to find a material that could withstand the phenomenal forces inflicted on the supersonic wheels. When the car is travelling at full speed they will spin at a phenomenal 10,500 rotations a minute, with the edges feeling a force of 55,000 times that of the Earth’s gravity. “We struggled to find materials that would hold together at those speeds,” says Chapman. It also needed to withstand the damage from small stones flying from the track and hitting the wheel like a round of ammunition. “Last thing you’d want is for it to fall to bits,” says Chapman. “If it cracked it would basically explode”

Testing Bloodhound's wheels (Stefan Marjoram)

A team of more than 130 stone pickers are already braving the desert’s dust storms and soaring temperatures to clear the track of all the stones they can find – but it’s not the kind of risk you can leave to chance. So Chapman’s team used a combination of mathematical simulations and physical testing – “we took different alloys and fired pieces of rock at them to see if they are susceptible to cracking” – to settled on an aluminium alloy that could stand up against these extraordinary conditions.

Next, Chapman had to find ways to stop them slipping across the sun-baked clay of the desert. Travelling at these speeds, rubber tyre would be torn off the rim – so the wheels will have to go naked. At first, the team designed them with a relatively sharp, “v-shaped” rim – which should give some grip to the surface, but early tests showed that they would dig deep trenches in the ground, unearthing stones that battered the aluminium. So they have now experimented with flatter, curved designs, with more success – they press down on the ground and provide some traction, but they don’t dig deeply into it. “You need the ground to squidge a bit to give softness,” says Chapman.

(Stefan Marjoram)

The team are also concerned about small slopes on the landscape. In a way, it’s the same principle as speed bumps – the faster you go, the more you’ll feel an uneven surface.  Given that Bloodhound SSC will speed across the length of a stadium in about a fifth of a second, even the slightest incline across could begin to shake the car. “These undulations could force the suspension to go into resonance and vibrate, making it very uncomfortable for Andy,” says Chapman. “It wouldn’t explode,” he adds, reassuringly – “but it wouldn’t be something you’d want to be sitting in. It would feel like driving a car along a rumble strip.” And there are also concerns about the wheels over-heating – in one short test they reached 90C (194F). “It’s one of those things you might not think about,” says Chapman, “but the air going the other way, past the wheels, is twice the speed of sound.” It is the resulting friction that heats the wheels.

Once these issues are solved, the team hope to start road tests in the UK – at a mere 200mph (322km/h) – in the middle of next year, before moving it out to the Hakskeen Pan, when they hope to finally break the 1,000mph barrier.

Will it be worth the wait for Chapman, years after that first conversation in the pub? “This is the best job and the worst job in the world,” he says. “I’m a lot greyer than I was when I started this project seven years ago. But the challenges you get are absolutely fantastic. I kind of describe it as engineering without a safety net. What we’re doing is pushing the boundaries so far aside from what people have experienced before.”

bbc.