Question

What is the physics involved with the giant trucks in the Monster Jam next month?

My boyfriend is a big fan of the Monster Jam and informed me the finals are in Orlando this year. From the videos I have seen, it seems like cars that drive around on very large hills of mud, dirt, and stuff. What is the physics involved with making such large jumps in a vehicle and how was the vehicle designed to take the impact from the stunts?

Answer 1

Since the moment when Missourian Bob Chandler jacked up his 1975 Ford F-250 and bolted on oversize tires to create Bigfoot, trial and error has refined monster trucks into true racing and freestyle-exhibition machines. Today’s monsters are built around tube-frame chassis and propelled by 1500-hp, alcohol-burning, supercharged V-8s. Their bodies are flimsy fiberglass that may (or may not) suggest a truck, a dog, or a superhero. Cape or no cape, monster trucks are subject to the same laws of physics that govern non-monstrous cars. Here’s how they roll:

A 10,500-pound monster that jumps more than 30 feet into the air comes down at 44.5 mph onto the junk cars beneath it. That results in an 8-g impact and 40 tons of destructive pressure. If only one wheel hits the roof of, say, a Ford Crown Vic, that’s about 25,000 pounds, well beyond even the latest roof-crush safety standard of three times vehicle mass. The front and rear suspension of a Patrick Enterprises truck consists of two longitudinal and two diagonal tubular-steel links locating each solid axle. There are about 26 inches of travel in the front and 30 inches in back with two gas-pressure dampers at each corner. “For racing, we want the suspension tied down,” explains Dan Patrick. “You can’t win while you’re in the air. But for freestyling, we want it loose, like a blown strut where the tire is bouncing up and down as it goes down the street.”

Using four-wheel steering to tighten its turning circle, a monster can whirl madly about its inside front tire. As the lean angle rises, the truck’s center of gravity moves over its outboard tires. Throw in about 1.5 g’s of lateral acceleration, and the truck will topple over.

ButlerBuilt has a specific high-back seat for use in monster trucks, with layers of high-impact foam strategically positioned throughout. The seat is bolted directly to the chassis, and a seven-point harness holds the driver in place. Although a truck may experience vertical decelerations up to 15 g’s, with a foot of deflection in the tire sidewalls, all that suspension travel, and four inches of foam under the driver’s butt, only about 4.5 g’s make it through to his body. Still plenty to endure 20 to 25 times during each event.