Possible Tire and Rim Sizes for P30/ P32

[eXodus]

My p30 came with 215/85/R16 E tires.  On 16x6 Steel Rims.

I think those tires are rather skinny.

What else can you mount? 
235/85/R16 ?
245/75/R16 ?

What wheels are fitting? Can I get wheels from any Chevy dually?

19.5 inch wheels?   

[Eyez Open]

You will find 19.5 tire selection rather skinny to, the dually rims  almost always limit tire size to 225's. 245's end up rubbing each other, and then there fat tire running on skinny rims,not good at all. Fat man in a little shirt? W%

[eXodus]

Not a expert in dually,

but can't you just put a spacer between the rims to prevent the rubbing?  Would also give the p30 a slightly wider track - which it definitely needs.
I got tons of space in the wheel arches. Putting on a wider tire/ wider rim shouldn't be an issue.

the 235/85/R16 would fit?

I was just wondering - since I got a Chevy Express 3500 - it has the same rear axle as the P30  and is running 245/75/R16 - it presumable has different rims then?

[Eyez Open]

Putting a spacer seems to be frowned upon, now as to why I cannot tell you. There is an individual on this forum who has quite practical advice and experience with suspension issues perhaps he will chime in. Changing tire sizes has quite a bit to do with suspension geometry which I tend to stay away from. That can become quite expensive in a short period of time..  It is rather frustrating to run around with a 15k rig in my case and a 6/7 inch tire print.

[eXodus]

the Rock Crawling folks are putting massive tires and spacers on the GM axles and beat the  out of them and those things still hold up.
Spacers get a bad rap when people are not doing all the steps. 

1. you need to get longer Wheel Studs. - which is a rather big job.
https://lugnut4x4.com/product/14-bolt-studs/
2. you need a centering spacers for you wheels.  (hub, lug OR wheel centering depending on your year and rim)


So It's not an REAR Axle issue - but your hint with the suspension geometry has maybe something...  Which I completely get on the front axel. The p30 front is way to complicated put together. But it also had been developed like 50 years ago where different tires had been available.

You are on the higher end of the scale of the p30 platform.  My class A is 6K lighter.