Somebody, please help me !

My a6 is little bouncing when my car go at high speed. On big flat surface it is bouncing strong and on shaded surface it is bouncing every 2 second little.

Because of bouncing my car is changing direction. What is the problem ?

Here is my exe file : level.rar

Please help me.

The Empire of the Mongols comprised the largest continuous land empire ever, reaching from Korea to Poland