How Can I Fix This?

When my car reach the max speed its start lagging.How can I fix this?

Code (CSharp):

1.   public float moveSpeed = 5f;
2.     public float maxSpeed = 60f;
3.     public float minSpeed = 5f;
4.  
5.  
6.     void Start()
7.     {
8.  
9.     }
10.  
11.  
12.     void Update()
13.     {
14.         if (Input.GetKey(KeyCode.W))
15.         {
16.             car.rotation = Quaternion.Lerp(car.rotation, Quaternion.Euler(-5, 0, 0), 0.03f);
17.          
18.             moveSpeed += 0.1f;
19.             if (moveSpeed > maxSpeed)
20.             {
21.                 moveSpeed = maxSpeed;
22.             }
23.      }
24.   private void FixedUpdate()
25.     {
26.  
27.         transform.Translate(0, 0, 1 * moveSpeed * Time.deltaTime, Space.World);
28.  
29.  
30.  
31.     }
32.      
33.         }

 

try putting the whole code from Update into FixedUpdate. This always workes for me