CHARLOTTE, N.C. -- It may be your car’s most important number. Not its horsepower, not its top speed, but its odometer reading.
That reading affects another important number: your car's value.
But what if the odometer, the very instrument that measures your car’s mileage, isn’t even accurate?
ASE certified mechanic David Lopez says there can never be 100 percent accuracy. Over the life of a car, that inaccuracy can really add up.
“If you keep the car to 150,000 miles, you may have 200,000 miles on it," said Lopez.
NewsChannel 36 wanted to measure the accuracy for ourselves, so we hit the Charlotte Motor Speedway. We brought four vehicles with us. All of the vehicles were different years, makes and models.
The speedway is a 1.5 mile track; so for our test, we looped it twice to get to 3 miles. The first test vehicle was a 2003 Chevy Cavalier. After resetting its odometer and starting the test, it blew past the finish line and kept going. We measured that the Chevy went 310 feet past three miles.
A 1998 Nissan Maxima and a 2009 Toyota Tundra also overshot three miles. The Nissan went an extra 164 feet. The Toyota traveled about 300 feet further than the Nissan.
The last test we performed was on a 2002 Ford Explorer, which is one of our mobile newsrooms. We drove it two laps, and its odometer was also off. It overshot 3 miles by 487.5 feet.
The Toyota Tundra had the largest error by more than 490 feet. That's an error of 3.1 percent. If the average driver puts on 15,000 miles a year, that’s 465 miles not being recorded. Over ten years, you could put 4650 extra miles on your vehicle.
We did some research and found out that margin of error is allowed. There are only laws against tampering with odometers, but no laws about accuracy. There is just a voluntary standard from the Society of Auto Engineers of plus or minus 4 percent.
So if you’re driving from Charlotte to New York City, your odometer could be off by more than 25 miles. That’s just one way, one trip.
“It’s buyer beware,” said LeeAnn Shattuck, who runs Woman's Automotive Solutions, a company that helps people navigate the car buying market.
She says a car’s mileage is a big factor in it’s worth, but so is how well it’s been maintained.
“You could have one person that is 40-years-old, and one person that is 50-years-old and their bodies could be very different depending on how well they’ve taken care of themselves. Cars are no different,” Shattuck explained.
The key she says is to look for normal wear and tear, as well as aftermarket addition, like the wrong-sized tires.
“One of the things people want to do when they upgrade a car, they want to put on larger wheels on it, and any time you change the overall diameter of the tire and the wheel by one inch, that will make your odometer off by 6 percent," she said.
“There is no standard in the industry.”
Coupled with an odometer that doesn’t have to be accurate, and you could be driving a car that’s worth much less than you think.
Shattuck and other automotive experts we spoke with say the best thing to do when purchasing a car is to have a certified mechanic look it over. You should also check the vehicles background by purchasing an online car history report.