duck

using UnityEngine;
using System.Collections;

public class Car : MonoBehaviour {

    Vector3 targetVelocity = Vector3.zero;
    float turnVelocity = 0;
    float maxSpeed = 100;
    float accelerationSpeed = 0.1f;
    float turnSpeed = 0.1f;
    bool onGround;

    void Start () {
        rigidbody.interpolation = RigidbodyInterpolation.Interpolate;
    }

    void OnCollisionStay(Collision col)
    {
        if (Vector3.Angle(transform.up, Vector3.up) < 65)
        {
            onGround = true;
        }
    }

    void FixedUpdate()
    {
        if (onGround)
        {
            Vector3 newVelocity = Vector3.Lerp(rigidbody.velocity, targetVelocity, Time.fixedDeltaTime * 3);
            rigidbody.velocity = new Vector3(newVelocity.x, rigidbody.velocity.y, newVelocity.z);
            rigidbody.angularVelocity = new Vector3(rigidbody.angularVelocity.x, turnVelocity, rigidbody.angularVelocity.z);
        }
        rigidbody.WakeUp();
        onGround = false;
    }

    void Update () {
        float v = Input.GetAxis("Vertical");
        float h = Input.GetAxis("Horizontal");
        targetVelocity = transform.TransformDirection(new Vector3(0, 0, Mathf.Lerp(rigidbody.velocity.magnitude, v * maxSpeed, accelerationSpeed)));
        turnVelocity = h * Vector3.Dot(rigidbody.velocity, transform.forward) * turnSpeed * (1.2f-Mathf.Clamp01(rigidbody.velocity.magnitude/maxSpeed));
     }
}