PORTLAND – It’s a tradition that dates back to the hot rods of the 1950s: Summer is nearly here and young Mainers are looking to “soup up” their cars.

But modifying cars and trucks with big rims, wide tires, lowered suspensions and free-flow exhausts sometimes causes drivers to run afoul of state law.

Something as simple as getting a state inspection sticker can be an obstacle if wheel rims are too large or the exhaust is too loud.

State officials say their only interest is in maintaining the safety of all drivers and upholding important standards in areas such as the environment.

For people who have invested thousands of dollars in their cars, it’s seen as a nuisance with a possible element of prejudice.

“They all just assume that we’re racing,” said Mike Card of Portland. “We’re just labeled the bad guys for some reason.”

In Card’s case, the reason is a black 1997 Mitsubishi Lancer with a carbon fiber spoiler, Japanese design body kit, racing wheels and a rebuilt engine. It also represents several years of work and, he estimates, more than $20,000 in modifications.

“It’s fun, it’s a hobby,” Card says, “but it’s very expensive.”

But as much good attention as he attracts with his car, there’s an equal amount of bad.

Driving home from Saco late one night after work, Card was pulled over in Scarborough. The officer questioned him on everything, from the size of his rims to whether his car had anti-lock brakes to the noise from his exhaust muffler.

He received a citation, but what he remembers most was the officer telling him, “You’re a criminal for changing your tires,” according to Card.

Lt. Chris Grotton, a member of the Traffic Division of the Maine State Police, said for the enthusiast, it typically comes down to a few things – wheels, exhaust or suspension.

There’s nothing wrong with changing the wheels or rims, as long as it’s only plus or minus two tire sizes recommended by the car’s manufacturer, he said.

Alterations to mufflers that make cars louder than when they left the assembly line are against the law, but there is an exception. Any exhaust system that is no louder than 95 decibels is permitted, but car owners have to seek out mechanics to test the noise level, he said.

On the other hand, any change to the suspension of a car with anti-lock brakes is against state law.

Customizing cars has emerged as a big business in the past decade, with sales of specialty equipment hitting $31 billion annually in the United States, according to the Specialty Equipment Market Association.

Peter MacGillivray, vice president of marketing and communications for SEMA, said the industry has been bolstered by a few factors, one being television shows such as MTV’s “Pimp My Ride,” which highlight custom work on everyday cars.

He also pointed to older Americans closer to retirement age who have the income to spend on the dream car they’ve always wanted.

“They’re realizing that their automobile is a reflection of their personality, not just an appliance that gets you to and from work,” he said.