How do i get my wheels to collide with the ground?

I am making a racing game and i have imported my own vehicle following this tutorial (https://www.youtube.com/watch?v=Wc6lUXOhRO0&t=630s)

I am having an issue with my wheels not colliding with the ground resulting in the car sitting on the body with no movement due to no traction.

any ideas on what could be causing this?
TIA