I love the way they look on your truck but I just can't seem to grow on the 19.5s on my truck. If I had some good tires I would love to go back to 16's on my truckThey'll almost surely be 225/70/19.5, that's what you see as factory size on most of those vans, on 3500HD's, on F450's, etc. very common size.
The ones in my pic above were 245/70/19.5 which are considerably taller and wider.
Richard