How Can I Suspension Effect?

I want when I press A or D the car moves and some rotations for suspension effect like Traffic Racer.I tried this code but its not looking smooth.What should I do?

private float curveAmount = 50.0f;
private float rotateSpeed = 100.0f;

if (Input.GetKeyDown("a"))
        {
            this.transform.rotation = Quaternion.RotateTowards(this.transform.rotation, Quaternion.Euler(20f, 0.0f, -curveAmount), rotateSpeed * Time.deltaTime);
        }

        if (Input.GetKeyDown("d"))
        {
            this.transform.rotation = Quaternion.RotateTowards(this.transform.rotation, Quaternion.Euler(20f, 0.0f, -curveAmount), rotateSpeed * Time.deltaTime);
        }

The WheelCollider object supports suspension directly.

Otherwise you’re pretty much reinventing your own physics.

For smoothness, you need to change the angle(s) over time, not all at once in one statement.

Smoothing movement between discrete values:

The code: Smooth movement - Pastebin.com

I dont want use Wheel Collider because my road is straight.I just need lane changing not car rotation that is why I only need effects.I hope I could explain and I am beginner.Do you have any advice to me about it?

Definitely start with any one of the over 200,000 tutorial videos. No need for someone here to type it all back in!!

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