Look rotation makes sudden changes with character controller

This is a racing game, I use http://arongranberg.com/astar/ pathfinder for the character runs on a oval racetrack. Player can only play with the characters speed which is calculated and has a high limit. When the player reaches high range of speed character suddenly looks left or right for a moment and straightens back and its very annoying. Its not happening with low speed. What am i missing? The dir vector is calculated same with the astar tutorials. I also use simple smooth modifier for the path. Rotation is all smooth and ok with speed 25 not 30 something or higher. I thought that it must be about character controller.

Code (CSharp):

1.  
2. dir = (path.vectorPath [currentWaypoint] - transform.position).normalized;
3. Vector3rot = dir;
4. if (rot.sqrMagnitude > 0.99f) {
5.       rot.y = 0f;
6.       vartargetRotation = Quaternion.LookRotation (rot);
7.       transform.rotation = Quaternion.Slerp (transform.rotation, targetRotation, Time.deltaTime * 10f);
8. }
9. characterController.SimpleMove (dir * speed * 0.8f);
10.  

 

My guess: the charactercontroller moves beyond the current waypoint on high "Speed". Which causes it to "look back"on rotating to the waypoint.

 

I found a solution:

When i checked the angles between dir and transform.position the values were like:

143.7691
143.8332
.
.
145.8065
.
.
52.40902 (eww!)
.
.
140.2589

I dont know why my direction vector changes suddenly. Now im checking for sudden angle change and it seems ok, probably not the best solution.

 

Are you sure, that the distance to the new point is far away enough? As I do not know your scene setup, it is just a guess, that, if your distance getting closer, your player turns to the point and gets that weird number?