RPM for Driving

using UnityEngine;
using TMPro;

public class PlayerController : MonoBehaviour
{
    [SerializeField] float speed;

    //RPM
    [SerializeField] TextMeshProUGUI rpmText;
    [SerializeField] float rpm;

    void FixedUpdate()
    {
        //rpm
        rpm = Mathf.Round((speed % 30) * 40);
        rpmText.SetText("RPM: " + rpm);
    }
}