Im with the 21.5 decision as well. As stated earlier, it provides a great progression in speed from VTA to Expert Sedan. It also provides a place for new people to the sport who dont want to buy new 25.5 motors or want to run the older style TA bodies to run before running 17.5 noboost/21.5 boosted sedan. (which is a slight issue at our local track. People new to the sport want the new style bodies, but arent ready skill wise for the 17.5 sedan class)