Your tires may look good on the outside, but could they contain a hidden danger?
Experts say tires can wear down with no visible signs of deterioration.
That is the result of oxidation, the same process that causes metal to rust.
A lawsuit says oxidation helped cause a blowout accident that left a truck driver permanently disabled.
"All of a sudden the tire came apart, flew up in front of the truck. I couldn't see out the windshield and next thing I know I was down in the brush," said truck driver Milford Stevens.
A crash on Route 422 in Butler County, Pennsylvania, left Stevens with a broken neck, traumatic brain injury and extensive nerve damage.
"It took his life. It just didn't kill him," said Donna Stevens, his wife.
Pictures of the tire taken after the crash show it was torn apart.
But the day of the crash, Milford did a visual inspection of the tires and found nothing wrong.
A week before the crash, a state police inspection report shows the truck and tires had no violations.
"I did not see any tire defects whatsoever," former Trooper Randall Michell testified in a deposition for the Stevens case.
Kumho, the tire manufacturer, said in court papers that the tire was "so worn and abused as to be illegal under state and federal law" and "no defect existed or caused" the accident.
But Stevens' attorneys said "premature oxidation in the subject failed tire" helped cause the accident and a similar defect was found in other crashes that led to lawsuits against Kumho.
"The tire essentially rotted from the inside out because it wasn't equipped with an appropriate anti-oxidant package that really stopped the breakdown of the rubber from the inside out as a result of oxygen molecules attacking the chemicals inside the rubber," said Wesley Ball, an attorney for Stevens.
The jury sided with Stevens and awarded him $3 million in damages.
A Kumho spokesman said, "We respectfully disagree with the jury's verdict in this trial. The product met all federal safety standards and there was no manufacturing defect found. Kumho Tire is currently considering our next course of action in regards to this case."
Stevens and his wife said most of the money will go toward medical and living expenses for the rest of his life, including care for the horses that they can no longer ride together.
"No matter how much, a dollar amount can't change the fact that he can't change a light bulb in the house," Donna Stevens said.
Ball said there is little that drivers can do to tell if oxidation is damaging the interior of a tire.
"It's like figuring out if the inside of an egg is bad when you get it right from the store. Until you crack it you don't know and unfortunately, it's kind of the same way with a tire," he said.
Tires are treated with chemicals that slow oxidation and delay deterioration. But outside of an X-ray, experts said it's difficult to measure interior wear and tear.
"You don't have tire health monitoring for things like deterioration, things like tread abrasion," said Swarum Kumar, an engineering professor at Carnegie Mellon. But Kumar is working to change that. His lab is trying to develop something like a tire pressure monitor that detects internal and invisible damage.
"Anything that we can do to help prevent these types of accidents can make a huge impact," Kumar said.
Milford and Donna Stevens hope something can be done to make tires safer.
"This put the screws to my life," Milford said.
Kumar said a tire can decay even while sitting on a store shelf. He said it is important for drivers to know how old their tires are and how long the manufacturer says they are supposed to last.