if you don't have it, just download it again from http://www.google.com/sketchup/download/

@frankenpengie said: Also I used the scale tool on the solid floor. When I change the width in relation to the car it's fine but if I lengthen the road the car falls through. Your wheels are square. Set them to be "convexhull" and it will work better. You can tell what shape the physics thinks the shape is by right clicking it and selecting Debug->Readback collision geometry. Then press play Scaling objects causes problems. Instead open the group and scale the geometry inside it. Chris