Unity & C# - car going a little bit unsmooth on ramp

I am making a racing game. When the car I made is going up on a ramp, it becomes a bit jittery. Don't think it's the camera issue as the game looks smooth on plain grounds and when going down a ramp. I followed this tutorial:https://www.youtube.com/watch?v=cqATTzJmFDY&list=PLllUqr_Vxwvto-j8J-Fk2XmjQhn2PcwlZ∈dex=2

I noticed that in this tutorial, the author's final outcome is also a bit jittery on ramps. This is the code:

 private void Start()
     {
         sphereRb.transform.parent = null;
     }
 
     private void Update()
     {
         speedInput = 0;
         if (Input.GetAxis("Vertical") > 0)
         {
             GetInputForMoving(forwardAccel);
         }
         else if (Input.GetAxis("Vertical") < 0)
         {
             GetInputForMoving(reverseAccel);
 
         }
 
         turnInput = Input.GetAxis("Horizontal");
 
         if (grounded)
         {
             Turning();
         }
 
         SetWheelsRotation();
 
         transform.position = sphereRb.transform.position;
     }
 
     
 
 
     void GetInputForMoving(float directionAccel)
     {
         speedInput = Input.GetAxis("Vertical") * directionAccel * multiplier;
     }
 
     void Turning()
     {
         transform.rotation = Quaternion.Euler(transform.rotation.eulerAngles + new Vector3(0f, turnInput * turnStrength * Time.deltaTime, 0f));
 
     }
 
     void SetWheelsRotation()
     {
         leftFrontWheel.localRotation = Quaternion.Euler(leftFrontWheel.localRotation.eulerAngles.x, (turnInput * maxWheelTurn) - 180, leftFrontWheel.localRotation.eulerAngles.z);
         rightFrontWheel.localRotation = Quaternion.Euler(rightFrontWheel.localRotation.eulerAngles.x, (turnInput * maxWheelTurn), rightFrontWheel.localRotation.eulerAngles.z);
 
     }
     private void FixedUpdate()
     {
         grounded = false;
         RaycastHit hit;
 
 
         //if hits ground
         if (Physics.Raycast(groundRayPoint.position, -transform.up, out hit, groundRayLength, whatisGround))
         {
             grounded = true;
 
             transform.rotation = Quaternion.FromToRotation(transform.up, hit.normal) * transform.rotation;
         }
 
         if (grounded)
         {
             Moving();
         }
         else
         {
             Dropping();
         }
 
         
     }
 
     void Moving()
     {
         sphereRb.drag = dragOnGround;
         if (Mathf.Abs(speedInput) > 0)
         {
             sphereRb.AddForce(transform.forward * speedInput);
         }
     }
 
     void Dropping()
     {
         sphereRb.drag = 0.1f;
         sphereRb.AddForce(Vector3.up * -gravityForce * 100);
     }
  

Please help I am really struggling. Sorry for my English, thanks in advance!