Quote:

My a6 car works OK on big shaded ground(block). When i change this block's shaded flag to FLAT , then my car will always bounce. What is the problem ?


The wheels have a tendency to bounce at polygon edges. If your non-shaded surfaces are a lot smaller than the shaded ones the car will be more bouncy. You can check the polygon size by hitting F11 twice.

If you encounter problems only with flat surfaces even though they are the same size as shaded ones then that would be a bug. I am not aware of that problem though.