Rex,
Wheel rotation has an affect on the vehicle and there are ways to simulate what the wheel is doing or where the air separating while rotating. Think of them as 4 pneumatic pumps on your car pumping air out in a radial direction. As you are up to speed the air is separating on the tire in a different location then non spinning. Years back when Eaker was at the GM tunnel some of the indy car teams would test with a "trip strip" on about the 1 o'clock location of the wheel (looking from right side), but then found that even without the "trip strip" they saw the same trends. In other words the incremental changes seemed to be the same and if they saw and improvement with a change on the car, it seemed to be the same whether the wheels were spinning or not. The absolute numbers will change a little, but the more important thing in wind tunnel testing is that when you get the car in the wind tunnel you start with X (baseline). Your goal then becomes how we are going to improve X to benefit the type of racing you do. No two wind tunnels will yield the same absolute #'s but if they are designed properly the trends and increments will be about the same. The reason these teams stopped using trip strips (I'm not speaking for all teams, just in this case) is because it is one more variable in the equation and if they don't get put on in exactly the right location and are not the exact size your numbers will be off from a previous test. So, I would say that there are ways to recreate wheels spinning in a wind tunnel that does not spin wheels, and you can learn very valuable information whether you spin, use trip strips or don’t spin. The more bells and whistles for your test (spinning wheels, rolling road, active boundary layer control, higher speeds, etc…) the more you will spend per hour.
The smaller frontal area would not make A2 any more precise. There is an adjustable ceiling that we move for each type of car we test to accommodate blockage and the bounding streamlines to facilitate accuracy. The precision in A2 is within 0.5% repeatability.
If you would like to discuss further feel free to call me: 704.799.1001 or dave@aerodynwindtunnel.com
Dave