I agree with Kevin K. I have tried Both bodies for mod and stock. The Speed 12 was more suited for mod by making the car feel more planted going into the straightaways out of a turn, which the 12b became to unstable and loose. The Speed 12b in stock seem to make the car alittle more faster and caused less scrubbing of speed in the turns while the 12 made the car alittle more slugish due to the downforce being applied. Mind you I tested on both surfaces asphalt and carpet. Both are good bodies, but each has their purpose on where and when to use them.