[Johnno]

Turn the car over and have a look at the chassis, you will certainly see the areas of the chassis that are scrubbing out on the track. 

My usual suspects are the bottom of the front splitter, the furthest point on the bottom front the chassis, even the NSR cars have been bottoming out on the overpass entry and exits on my track. 

Easy fix is to install grub screws on the top and bottom of the axle and adjust them all slowly to increase the front height of the car, essentially lowering the wheels onto the track adding chassis height