How can I rotate these wheels the correct way?

I am new to Unity and scripting, recently I have been following this tutorial on Youtube on how to make a mobile optimised car game. So far everything has worked out well except the wheel rotation when the car is moving. The wheels rotate when driving but the wrong way. Currently they spin horizontally (like a penny spinning on a table) Here is the script for the wheel rotation

rotationAmount = carRight * (relativeVelocity.z * 1.6 * Time.deltaTime * Mathf.Rad2Deg);

What can I add to this to make the wheels rotate the correct way or on the correct axis?

I could be mistaken but couldn’t you change 1.6 to -1.6 and it would roll the other direction?