bearingburner,
I would mainly consider "tank" style bodies as they are inherently aerodynamic, flat sided dragster style bodies, many of which have either no body work behind the rear wheels or have a tail section that is to short and the transition from the main body to the tail section is an abrupt transition will typically have the rear wheels close to the body and it probably does not make much difference as the wheel/tire completely disrupt the air flow anyway. Yes there are some flat sided cars that have gone very fast, that is usually because they have really strong engines and I also know that the very successful J,I,and K class lakester, the Bockscar ,is flat sided and the rear wheels are fairly close to the body but the success of this car probably shows what the minimum wheel/tire clearance should be to have good air flow over their very aero rear body shape. It also shows that Stainless builds some really killer motors!
rex