TIRES

NEW TO SIGHT WHATS THE SMALLEST TIRE I CAN PUT ON A CREWCAB DUALLY WITHOUT MESSING UP MY TRUCK

Messing it up in what way? I have 19's (Outer) and 16's (Inner) and
I'm using a Low Pro Street Truck Tires. (And I tow with it) As long
as you get the "XL" rated you should be fine. If that doesn't give
you the answer you wanted, give us some more info on question.

I have 16s on it i want to put a lower profile on it . The guy at the shop said the weight would wear the tires out quicker or they might blow. also can I mill down 19.5s to size 18??? dont want 22s

19.5's can only be milled to 19, not enough there to go down to 18.

Yes, you can have issues with any low pro tire on a Dually, but the
XL rated tires have stronger sidewalls. (Why I chose my tire sizes)

Sometime this year, supposedly, there's a 20" direct bolt on coming,
but I've been hearing of larger direct bolt on's for over a year + so
I have no idea when it will actually become a reality and available?

I hear that- I'll believe in the 20" when I see them.

lol

Live in Los Angeles anybody know where i can find some 8-lug 19.5s used and where can i get them milled to 19s

Tennessee tire and wheel

Yeppers, Trevor did mine, and trust me you don't want
just anybody to turn down rims. (He will ship em to ya)

Gud lookin do they have a web site