How to i make a gear system from this script? help please

Hello, i searched this from a long time, how to i make a gear system from this audio pitch script? (depending the car speed) Thanks!
var minPitch : float = 1.0;
var maxPitch : float = 2.0;
var maxSpeed : float = 20.0; //tweak to your vehicle

private var pitchModifier : float;
 
function Update(){
    var currentSpeed = rigidbody.velocity.magnitude;
    pitchModifier = maxPitch - minPitch;
    audio.pitch = minPitch + (currentSpeed/maxSpeed)*pitchModifier;
    

 if(audio.pitch > maxPitch)
 {
 audio.pitch = maxPitch;
 }
}

Fixed!

var minPitch : float = 1.0;
var maxPitch : float = 2.0;
var maxSpeed : float = 20.0;
var pitchLimit : float;
var guear : int;
var maxSpLimit : float;
var GuiStyle : GUIStyle;
var Escapes : ParticleSystem[];

private var minGuears : int = 1;

private var pitchModifier : float;
 
 
function OnGUI ()
{
   GUI.Label(Rect(5,5,200,200), "Cambios : " + guear, GuiStyle);
}
 
function Update(){
    var currentSpeed = rigidbody.velocity.magnitude;
    pitchModifier = maxPitch - minPitch;
    audio.pitch = minPitch + (currentSpeed/maxSpeed)*pitchModifier;
    
 if(audio.pitch >= 1.5)
 {
 maxSpeed += 30;
 audio.pitch -= 0.4;
 guear += 1;

 }
 
 if(Input.GetAxis("Vertical") == -1)
 {
 maxSpeed -= 30;
 guear -= 1;
 }
  if(Input.GetAxis("Vertical") == 0)
 {
 maxSpeed -= 30;
 guear -= 1;
 }
if(Input.GetKey(KeyCode.Space) && guear > 1)
{
maxSpeed -= 30;
guear -= 1;
}


if(guear < minGuears)
{
guear = minGuears;
}
if(maxSpeed < maxSpLimit)
{
maxSpeed = maxSpLimit;
}

}