When most people imagine chariot racing in ancient Rome, they likely picture the thrilling race portrayed in the epic blockbuster "Ben-Hur." Yet it's unlikely the heavy chariot driven by Charlton Heston would ever win a real race.

That chariot wasn't just hopelessly huge and heavy — it did not have proper tires.

A study of a 2,000-year-old toy chariot found in the Tiber River in the early 1890's and now on display at the British Museum, has revealed a secret trick. To increase the winning chances in the Formula One of the ancient Romans, an iron rim was mounted on the right wheel only of the two-wheeled chariot.

"The basic wheels were always of wood, animal hide glue, and rawhide strips (at critical joints) that tighten upon drying, like clamps," explained author Bela Sandor, professor emeritus of engineering physics at the University of Wisconsin at Madison. "Any iron tire for racing would be a very thin strip of iron on the outside of the wooden rim, best when heat-shrunk on the wood, to consolidate the whole wheel.

Adding the strip of iron to the right wheel improved a charioteer's chances of winning a race to roughly 80 percent, according to a study published in the latest issue of the Journal of Roman Archaeology.

"The solution makes full sense in engineering thinking, ancient or modern," Sandor told Seeker.

Unfortunately no actual Roman racing chariots have survived. The archaeological evidence for the single-tire configuration only comes from the small toy model now on display at the British Museum.

A toy model of an ancient Roman, two-horse racing chariot. Credit: Bela Sandor

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Representing a biga, a two-wheeled racing chariot driven by two horses, the hand-sized bronze model is lacking one of the two galloping horses as well as the charioteer.

The bronze chariot was probably a toy for a rich individual, perhaps even Emperor Nero, who, according to 1st-century historian Suetonius, used to play with toy chariots.

"The wheels originally rotated freely on the axle. It was made by someone who knew a lot about racing chariots," Sandor said.

Using the toy model and independent estimations as a guide, Sandor was able to establish the major dimensions of Roman racing chariots. He concluded that a typical Roman vehicle weighed about 25-30 kg (55-66 pounds) had a track width of about 155 cm (5 feet), a wheel diameter of about 65 cm (2.1 feet) and a pole of about 230 cm (7.5 feet).

Among the details of the Tiber model, the British Museum's Judith Swaddling and Sandor noted a slightly raised rim only on the right wheel, indicating a thin iron tire reinforced the wheel.

"Two identical wheels would have been easier to produce for toys and real chariots alike. But a high-ranking customer would probably demand for his sophisticated toy an authentic representation of reality, if indeed that was one tire only," Sandor said.

A detail of the wheel in the Tiber model showing a slightly raised rim. Credit: Bela SandorPhoto: Bela Sandor

Since it was easier to guide the horses into left-turning bends, most races ran anti-clockwise.

"Indeed, the right side tire works best in oval-shaped arenas if the turning is always leftward," Sandor said.

Sandor explained that some of the Romans strengthened the right wheels only because all chariots leaned to the right and overloaded just the right wheels during the left turns.

"This makes total sense to everybody who understands the dynamics of a turning vehicle. It's a common sensation to people riding in a fast-turning vehicle; standing and lurching sideways in a turning bus is a good example," Sandor said.

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Although the single iron tire configuration did not always produce a faster machine, it likely prevented wheel failure and crashes and so it was statistically superior in racetracks.

"Without any iron on the wheels, the right wheel was failing often and predominantly, while both wheels having iron tires tended to be safe but were seldom a winning combination," Sandor said.

Overall, Sandor estimated that chariots with no iron tires had a 50 percent chance to win, while vehicles with two iron tires had only 30 percent probability of success. The Ben-Hur movie chariot would have had less than 5 percent chance of rolling to victory.

"A racing chariot with an iron tire on the right wheel only was the best compromise in terms of safety, durability and winning probability," Sandor said. "As the finest available representation of a Roman racing chariot, the Tiber model gives us a glimpse into the Romans' probabilistic thinking for winning races and bets."

According to André Veldmeijer, visiting research scholar at the American University in Cairo, the study reveals how much more there is to learn about the design and strategy behind ancient chariot racing. As he told Seeker, "Chariots, despite the numerous studies and increasing scholarly attention, have not yet revealed all their secrets, as this study clearly shows."