Downloaded Bus Jumping!

My Downloaded Bus jumping in big map (92). Normally bus doesn't jump. My downloaded bus is FBW 549.

My settings:

Graphics

reduce the target frame rate to 55

Max. Obj. Visibility distance to 90

... For reflexions 0

Real time reflexions None (i know that isnt the same to play without the mirrors)

Particles sistem 100 till 300

plus no P.S. in reflexion

Graphics (Advanced)
Remove Bump map, limit all bus to 256 pixels and put Real Time Reflexions to 1