When NASCAR driver Kyle Busch suffered a race-ending crash while leading the Daytona 500 in February 2017, he wasted no time casting blame on Goodyear, the tire manufacturer and official provider of NASCAR’s highly engineered and specialized tires.
Race car crashes can result from almost any problem—a miscalculation on the part of the driver or pit crew, poor weather, a mechanical failure—but the Kyle Busch-Goodyear episode reflects the make-it-or-break-it status of tires in car racing. From the composition and texture of their surface materials to their minutely measured diameters, race car tires are some of the most precisely engineered hunks of rubber and metal in existence. Indeed, if it weren’t for their top-notch tires, race cars would be high-horsepower hunks of metal.
It should come as no surprise, then, that tires were of similar importance to Kyle Busch’s ancient equivalents in the world of Roman chariot racing—a hugely popular sport that drew legions of fans for 1,800 years.
And yet, it took a retired engineering professor studying a toy model pulled from the Tiber River to establish that the ancient Roman chariot racers were as fixated with the performance of their tires 2,000 years ago as Kyle Busch is with Goodyear’s tires today.
Bela Sandor, professor emeritus of engineering physics, retired from decades of teaching and research at the University of Wisconsin-Madison College of Engineering in 1997. In the two decades since, Sandor has turned his longtime interest in ancient chariots into a robust line of academic inquiry, bringing engineering expertise to the inexact science of archaeology.
Sandor wants to understand how the two-wheeled vehicles ubiquitous in the ancient world—from Rome to China and India to Nubia—were engineered. In the process, Sandor has discovered many design features of both Egyptian and Roman chariots. Over the years he has been building the case that the ancients were far more technically sophisticated in their chariot design than modern archaeology scholars have often given them credit. Sandor’s first discoveries used actual ancient chariot specimens, but his most recent discovery, made with the assistance of a toy model, involved a higher degree of inductive sleuthing.
Sandor’s first big splash as an archaeo-engineer came in 2004 with the publication of a paper he authored about the sophisticated design of ancient Egyptian fast chariots found in King Tut’s tomb. The paper appeared in the Oxford Journal of Archaeology—a journal unaccustomed to receiving manuscripts from engineers. The novel discovery—not to mention the novel origin of that discovery—led to considerable attention and eventually became the basis of a popular episode of PBS’s science program Nova, featuring Sandor and other experts on ancient chariots and building techniques.
The discoveries detailed in the Nova special were related to what Sandor terms the “Tut-class” chariots—Egyptian chariots that the half-dozen discovered in Tut’s tomb are thought to represent. Although the ancient Egyptians shared technological expertise with their Roman neighbors, the Romans’ dedicated racing chariots were unique and, because of a dearth in surviving specimens, not as well understood, says Sandor.
“Of all the chariots that have been used in history—there have been literally millions—there are very few in existence today. And there’s not a single Roman racing chariot left in existence,” Sandor says.
So what is an archaeo-engineer to do? Like most archaeologists, Sandor has depended on art to illuminate the ancient world. Thousands of paintings and mosaics survive that richly—and in large part accurately—depict the Romans’ obsession with chariot racing, complete with depictions of catastrophic crashes. It was these crashes—often shown as occurring on the oblong Roman racetracks’ tight corners—that particularly interested Sandor.
While at UW-Madison, Sandor taught fundamental engineering courses, including statics and dynamics, and his expertise is in fatigue and fracture. He knew that Roman chariot teams, just like modern drivers, would deal with two competing aims—speed and safety. The aim for speed was aided by a light-weight vehicle, which would mean an easier load for the two or four horses. But lightweight construction included all parts of the chariots, including the wheels. A lightweight wheel could also prove to be a weak spot.
Those weak spots often led to catastrophic crashes, which were more likely to occur around the track’s tight corners, where the speeding chariots would lurch rightward as the horse-drawn vehicles turned sharply left. It’s a concept that anyone who has ridden a standing-room-only bus is all too familiar. And, just as people today who may not be aware of the forces involved in a fast tight turn can still intuitively understand its implications and brace themselves, Sandor was sure that ancient Roman chariot racers were acutely aware of, and would have wanted to brace for, sharp turns in the track. But the Romans’ frescos, detailed as they are, did not on their own reveal what, if any, features the Romans built into their racing chariots to brace against this stress to the right wheel.
Enter the toy model. Keen on learning anything he could about how the Romans optimized their racing chariots, Sandor traveled to the British Museum in London. The museum houses a spectacular collection of artifacts from the ancient world, including such stars as the Rosetta Stone and the Elgin Marbles, but Sandor was interested in an item of little stature—a bronze toy chariot small enough for a child to hold with one hand. Sandor calls it the “Tiber model” because it was discovered in Rome’s Tiber River in the 19th century. It’s believed to have been cast in the 1st or 2nd century CE, and it’s a remarkably detailed and seemingly accurate model, Sandor says. Even though it is literally a toy—the Roman equivalent of a Hot Wheels toy car—the model is the best three-dimensional depiction of a Roman racing chariot known to scholars.
That’s why a curious feature Sandor noticed while examining the model in a museum study room is so intriguing. A small ridge encircles the rim of the right wheel. Crucially, the ridge is present only on the right wheel—the left wheel’s rim is smooth, without a ridge. Sandor believes the right wheel’s ridge is possible evidence that at least some Romans engineered their chariots to compensate for the large stresses acting on the right wheels. He believes the ridge represents an iron tire, which bolstered the right wheel to withstand the hard left turns.
“Iron is heavy, expensive and difficult to work with, so ideally the Romans would not have any iron tire for racing to make the chariot lighter and to accelerate faster,” Sandor says. “Small differences in this kind of situation make a big difference in the competition.”
Drivers were faced with a few options, Sandor believes: fit iron tires onto both wheels, the right wheel only or neither wheel. Iron tires, while reinforcing the wheels, would weigh them down. The tires would also alter the wheel’s distribution of mass in a disadvantageous way, slowing their acceleration potential by increasing their rotational inertia. Sandor believes the Romans understood these concepts, and that many chariot racing teams would strike a balance between performance and safety, much like modern engineers. And in competitive sports like chariot racing, minor tweaks to equipment can significantly affect outcomes.
“If I were in their shoes, what would I do?” Sandor asks. “Do I want to make sure that I always finish a race? Then I’ll have two iron tires. Do I want to take the biggest gamble of them all and not have any iron tires? Then some of the races I will lose because my chariot will fall apart. Or do I want to average my luck and do something that helps me win, say, two out of three races?” That “something” would be fitting an iron tire on the right wheel only. And Romans were likely calculating things like win/loss probabilities, Sandor believes.
These types of thought experiments come naturally to Sandor, a born competitor who, at the age of 82, continues to swim competitively and enjoys strategizing. He says that this mindset—a combination of a curious imagination tuned into strategy and a knowledge of engineering fundamentals—has led him on a pursuit that would not be considered mainstream archaeology.
“Now I’m getting into psychology,” Sandor says. “This is not traditional archaeological thinking. I’m getting into the psyches of the drivers and owners and the engineers and everybody involved with the racing team,” he says, adding with a laugh, “Maybe even the horses, because horses like to win too.”
The findings are supported by modern race car engineering, which also often features vehicles designed with bolstered right sides as most car races—like the ancient Roman chariot contests—run counterclockwise around a track.
“In high-tech Indy races cars are engineered to be left-bent,” Sandor says. “In these racing cars, the tires are not all the same. The right-side tires are heavier and are slightly bigger in diameter because they are turning left and they want their machines to be naturally drifting left.”
Sandor’s Tiber model findings were published in a paper titled “Tire choices in Roman chariot racing,” which appeared in the Oct. 31, 2016, issue of the Journal of Roman Archaeology. The research, along with interviews with Sandor, have since appeared in many news outlets, particularly in Europe. Sandor says that his findings have been well received in academic circles as well.
“I’m convinced that this is how things went,” Sandor says, referring to the right-wheel iron tire phenomenon. “I haven’t received any real argument against any of my discoveries. Sometimes people have questions, and some of them are good questions, but no one has said that I’m wrong. I might be. That’s always possible.”
But for a man inclined to consider hypothetical outcomes probabilistically, Sandor is happy with his odds. As he continues exploring other questions, Sandor hopes more archaeologists will apply technical expertise to solving historical problems, or better yet, that more engineers become interested in archaeological questions.
“In the engineering community few people are interested in these topics,” Sandor says. “There’s no money in it. So the only interest that exists is in an education sense, and there are some fabulous, challenging topics. There are some PhD theses here.”
Author: Will Cushman