Choppy movement of moving quad with rotating camera

Hi everyone! I'm making a similar Mario Kart game. I'm using Quads, one for the ground, and one for each racer. The quads use billboarding to always face the camera (May I clarify that the ground stays put, only the racers use billboarding).

In the main menu I set the camera to rotate along the center of the track while the AI racers run in the track.

My problem is that the racer's Quads move a bit "jerky/stuttery/flickery/choppy" (I googled a lot and found a question using those terms, as non native English speaker, I THINK those describe my problem pretty good)

To move the camera I use:

 transform.LookAt(Vector3.zero); // To always face the center of the track
 transform.Translate(Vector3.right *10* Time.deltaTime); // To move in circle along the center of the track

For the billboarding in the racer's quad's, I use either this:

 //transform.rotation = Camera.main.transform.rotation;

Or (currently) this:

 var fwd = Camera.main.transform.forward;
 fwd.y = 0.0f;
 transform.rotation = Quaternion.LookRotation(fwd);
 

To move the racer's quad's I use:

 transform.Translate(Vector3.forward * Time.deltaTime * CurrentSpeed);

Thanks in advance!

EDIT: Not sure if it helps, the racer's quad have a RigidBody attached to them and a Mesh Collider as Trigger. The rigid body has "use gravity" unchecked and is only used alongside with the mesh collider to detect trigger events