When I purchased my Johnex, I was told that the original body used to make the mold was "off" a bit, side to side in the rear. The Johnex uses a live axle that is mounted with a modified DeDion (sp?) suspension which is fully adjustable. Recently a friend who races Dirt modifieds was visiting me and described my rear suspension as a form of a "Z" link setup. This suspension allows me to adjust it just about any which way.
With the live axle right center on the frame, one tire would be about to rub the body while the other one had a good inch to spare. I moved the axle sideways about a half inch and then squared up all four wheels. Now the body appears to centered over the tires. That was 5 years ago and the car has always tracked perfectly straight with no problems. What 496fe said worked for me.
Wayne