The shaking is rounding errors / lack of decimal precision in the 3D rendering. It is due to the size of the track. It's called popping and due to single precision in XY grid coordinates in the driver. Basically on each frame, at map extents, the final 3D rendering of every asset results in a very slight difference due to lack of decimal precision. This shows stuff moving around very slightly. It's not physics or cars. Evo triangle shows this also in places. At centre of the map it will be stable as near the origin (0,0) - with most decimal places available for precision. Nearer the edge of the map you will have the most popping due to the XY being a big number with limited numbers/precision in the decimal portion. Sorry for poor wording but trying to make simple.