Automakers may be obsessed with cutting vehicle weight, but they are happily packing on pounds in one place.
Giant sunroofs and skylights dominate many new-vehicle cabins. The treated glass provides natural light and can be as strong as steel. But the glass can add several more pounds than steel, depending on the size of the opening. And an open sunroof interrupts airflow over a vehicle, increasing drag and reducing fuel economy.
"What we're seeing is that more people are trying to bring more light and energy into the vehicle," said John Thomas, vice president at sunroof maker Webasto AG.
Webasto says it supplies about 55 percent of all original-equipment sunroofs used worldwide. Though sunroofs and skylights are getting lighter with the use of aluminum frames and thinner glass, Thomas said automakers carefully monitor the percentage of vehicles on which the features are installed.
If the heavier sunroofs make up more than a third of a vehicle's production mix, the vehicle's fuel-economy testing must include the feature.
Still, big glass has been a growing trend on the roofs of luxury vehicles for several years, and recent advances in sealing and mechanics seem to be expanding that trend.