Semis rolling down Iowa’s highways are starting to look a bit different. Some trucking companies are now using what are called “super singles,” a wider tire that replaces double sets of trailer tires. Scott Weiser, president of the Iowa Motor Truck Association, explains the benefits. With the wider single tire, there’s less rolling resistance and better fuel economy. The trailers are more maneuverable and there’s also less weight in the absence of all those tires, so the truck can carry more cargo. Weiser says the super single may eventually eliminate the concept of an “18-wheeler.” At the back of a semi-trailer, there are four sets of double tires. The super single reduces that cluster of eight tires to just four tires. The new tractor-trailer truck looks essentially the same but is a 14-wheeler. Weiser says the super single isn’t a good fit with every trucking operation, but is being embraced by some outfits. Another way truckers are looking for better mileage is by using tires equipped with automatic inflation systems that constantly keep them at the proper pressure.