The primary advantage of running both Cup and Xfinity Series races is extra practice ("seat time") for the drivers. Xfinity races are often run as support races a day prior to Cup Series races, and use similar equipment, though Xfinity cars have less horsepower than Cup cars. Some racing experts suggested that when the Cup series transitioned to the safety-oriented Car of Tomorrow in 2007, the advantage of Cup drivers racing in these events would decrease greatly due to differences in the designs of the vehicles. However, this did not decrease the presence of Cup drivers in the series, as each Xfinity Series (then known as the Nationwide Series) drivers' title from 2006 to 2010 was won by a Cup Series regular. The aerodynamic differences of the two series were greatly reduced when the Nationwide Series implemented its own Car of Tomorrow in 2010.