Stun Armor on Vehicles that ignore Stun?

[Skiri-ki]

As the Title Suggests, I'm currently a bit baffled as to why Vehicles have Armor ratings like the Impalas 1S 1W when Stunn is ignored from the get-go
Basically, if my Car hits a Tree for d8 Basic and I'll just assume i get an 8 from that roll
that means i get 4S + 4W with a reduction of 1S and 1W, and then i drop Stun anyways and get 3W?

This is how it's written in the original Cortex rules as well. I could see that an Armor of 1B 1W would make sense but 1S 1W is just fancy for 1W really...

1B 1W in the example woud make 8B-1B -> 4S + 3W-1W -> 2W

I think, for now I'm gonna treat it as 1B 1W and otherwise hope the players will not hit the tree anyways but if they do I'm prepared XD