It’s one thing to own your own monster truck. It’s quite another to own nine.Bill Payne has made a monster of a business with Straight Up Racing. One of his trucks — a blue colossus on 66-inch high wheels named Sapphire — will be at the San Joaquin Asparagus Festival, which starts Friday at the county fairgrounds.

Payne dispatches monster trucks to fairs, festivals and other events across five states and Canada. All of his trucks are built for thrills, with some that fly through the air during performances.

In others, like Sapphire, Payne has installed seats in the truck bed. The customization allows passengers to experience heart-pounding action while riding in the truck as it whips along a dirt track, making tight twists and turns.

The sheer size of the vehicles, their roaring, 430-horsepower engines and bright paint jobs make monster trucks a natural draw for fairgoers, especially kids, Payne said.

“You put a monster truck out in front of the kids, and they are saying, ‘Mom, ooh, ahh, look!’ ” he said.

Payne started the business 23 years ago. He loved off-roading in jeeps and discovered he could make a business giving people thrill rides. He built his own vehicle at his shop in Port Orchard, Washington.

“When you build them right, you build them strong. We build everything in-house,” he said.

It’s not a cheap venture. A single tire for a monster truck costs $4,400. Payne says tires have to be replaced every two years on some of the trucks.

He has a trustworthy crew of six to help with the work, including hauling the trucks to shows and festivals. He finds workers who love the trucks as much as he does.

“One of my main guys, he was a fan as a kid. Now he works for me,” Payne said.

It’s a busy schedule. His drivers are on the road 44 weekends of the year, hawking monster truck rides for $10 a passenger. Sapphire, powered by a 540-cubic-inch Chevrolet engine, seats 12, and expects to see plenty of action this weekend.

Despite the heavy workload, Payne said he wouldn’t have it any other way.

“The amount of fun outweighs the amount of work.”