I did some testing today with three Thunderslot chassis in both the spyder and coupe bodies. All three chassis had trued original front tires on stock plastic wheels. One chassis had trued original treaded rears, the other two had trued Thunderslot slicks. One of the latter chassis had a small weight in the nose, the other two had no weight added. I made two runs of 10-15 laps with each chassis in the spyder, the coupe, and the coupe with the rear track widened about 2mm to fit the wider coupe body. I recorded fastest lap and median lap in each run.
The first chassis with the trued, treaded rear tires was not optimized and there was some tire chatter. This was the slowest chassis with the least amount of track time. The median times and best times between the spyder and the coupe were virtually identical. After widening the rear track, both the median and fastest time improved about .1 sec.
In chassis number two, the times were just about the same in all runs and variations. There were slight time variations between runs with the same setup, but all the differences were so small as to be considered testing error. There was little difference if the rear track was widened.
In the fastest chassis, with the nose weight and the most practice laps, the spyder’s fast lap and median lap were both about .1 sec. faster than the coupe. After widening the rear track, the coupe narrowed the times to about .05 sec. behind the spyder.
These tests were done by just swapping the chassis, setting the mounting screws to about the same amount of body float. No tweaking was tried to optimize setup.
My conclusion from this is that the cars are close enough as is, especially if the coupe runs with wider rear track, so I stand by the rules as written. When new cars come out, they will need to be checked against existing cars.