Tear-offs add new layer to windshield safety

It's a part of the car that has changed significantly since the days of "strictly stock" NASCAR racing -- the windshield. Although many safety improvements have been made in the sport over the years, the introduction of the polycarbonate windshield not only protects drivers from injury during a crash, but it changes the way drivers see the racetrack -- literally.

When the first NASCAR-sanctioned race was run in Daytona in February 1948, traditional windshields were made of tempered glass, designed to shatter upon impact. Detroit's introduction of safety glass, two pieces of glass with a layer of vinyl sandwiched between, brought improvement to the series in the 1950s.

It wasn't until the 1990s that the windshield standard changed yet again, this time with the introduction of the polycarbonate windshield. Also known by the brand name Lexan, the new material was considerably stronger and safer for drivers.

But polycarbonate windshields are not perfect. While the exceptional strength of the material prevents shattering of the windshield upon impact with an object, it is easily scratched because it is very soft. Objects that hit it scratch, dent or imbed in the windshield, causing very poor visibility.

Steve Peterson, who until his death Tuesday was NASCAR's technical director since 1995, had been instrumental in the development and implementation of such safety features as the SAFER Barrier, head and neck restraints, improved seat belts, cockpit surrounds, seats and fire safety.

"There was a lot of work done in the early days with coatings on the polycarbonates to make them more scratch resistant and not show swirls or circles when in high ambient light like driving into the sun," Peterson said in an interview last month. "There were times when we first started using Lexan that we would have to change the windshield between the Happy Hour session and race morning and put a new windshield in because it would become so scarred and scratched.

"That was particularly true at the tracks that had an abrasive surface like Darlington and Rockingham, and even at Michigan and Daytona, some of the high-speed racetracks.

"One of the last things you'd see the crew members do when they left on Saturday evening to go to the motel was to put the car cover on. But they'd have plastic cups taped to the top and sides of the windshield to let the silicone that was used to install the windshield dry overnight, with the cups holding the car cover off of the windshield so it wouldn't screw it up. But in the last 10 years, there has been the addition of the clear overlay windshield tear-offs. Those have become optically perfect."

Teams apply several layers of an adhesive film to the windshields that can be peeled off during pit stops, revealing a clear layer and leaving the Lexan unscratched. Peterson said the teams buy the tear-off materials directly from a distributor.

"In some cases, they buy it in sheets and cut it out, but in most cases it comes from a supplier who will have already pre-cut it and pre-shaped it so it matches the curvature of the windshield frame," he said. "They have some very sophisticated molds and tooling. They basically put the windshield over the tooling and then apply infrared heat until it forms to that shape. Then they let it cool to hold that shape until it is installed in the car."

The windshields are usually constructed from three relatively flat pieces of Lexan. Each piece is supported by a framework built into the roll cage, including what is known as the "Earnhardt bar," a metal brace located across the middle of the windshield that keeps the roof of the car from collapsing during a wreck. The bar came into use after a 1996 crash at Talladega Superspeedway when the roof of Dale Earnhardt's car caved in while the car slid across the track upside-down.

Tear-offs are "tabbed" to separate the films so the over-the-wall pit crew member assigned to the windshield can pull them off one by one.

Peterson said that during car fabrication, usually a mock-up windshield goes in very early in the process, with the actual race windshield typically not installed until what is known as final fab, after painting is completed.

The windshield is part of the NASCAR inspection process, requiring ¼-inch minimum thickness on the front windshield and 3/16-inch on the side glass quarter-windows and rear glass.

"We look for the minimum thickness, and there are a certain number of bolts and tabs that are required," Peterson said. "Those bolts and tabs have to be a certain diameter, and in some cases, they have to have nuts on the backside. In other cases, they can thread it into a threading device that's bolted in a portion of the windshield frame.

"Most teams I've talked to say they can't use more than five tear-offs," Peterson added. "That's kind of the limit until you start getting some opaque qualities that the drivers don't like. It varies on whether it's a day race transitioning into night or if it's just a day race."