C# Min/Max Rotation based on Float?

I am trying to work on a non GUI speedometer. I have my speed float set up and am trying to work out how to get the needle of the dial to rotate from a minimum angle to a maximum angle depending on the value of the speed float. Any help would be much appreciated!

using UnityEngine;
using System.Collections;

public class Speedos : MonoBehaviour {

    //My speedometer needles.
	public GameObject RPMSpeedo;
	public GameObject MPHSpeedo;

	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
	
        //Speed float value.
		GameObject sedan = GameObject.Find("Sedan");
		RCCCarControllerV2 sedanScript = sedan.GetComponent<RCCCarControllerV2>();
		sedanScript.speed -= 0f;

	}
}

Something like this should work:

float angle = Mathf.Clamp((speed-MIN_SPEED)/MAX_SPEED*(MAX_ANGLE-MIN_ANGLE)+MIN_ANGLE, MIN_ANGLE,MAX_ANGLE);
NeedleObject.transform.localRotation = Quaternion.AngleAxis(angle, NeedleObject.transform.forward);

Maybe you have to use transform.up or transform.right instead of transform.forward, depending on the orientation of your gameobject.