Right now by Roar Rules its by motor class, 17.5, 13.5, or mod. Every one so far is doing 4 cell racing. If you would like to use a 1S in that class it is your choice. A possible 1/12th lipo class from Roar is not planned until the 2010-11 season. Roar is waiting because not all 1/12th cars can run a 1S lipo and so are we.