Tyre size

[NigelW]

I currently have 255/45/19 tyres on my A8.
I would like to have 285/40/19 tyres.
Do they fit the front and back, just the rear or not at all?

Thanks for advice.

Edited November 30, 2020 by NigelW
Incomplete

[NigelW]

Was told not to change by Audi dealer - so I haven’t.