Aerial coax length

[Rustydiver]

Is there a minimum length I should have.
I've mounted my aerial on my old vw van at the front where the car aerial was so don't need a long length. Going to give it a go there first, if it don't work we ill I will then mount at the rear higher up.
The aerial now still sticks up a few feet above the roof.

[stampman]

no dosent matter about length will still swr