How Much Backspacing Is Too Much?

I am considering buying aftermarket wheels probably in the 16x6 or 7 category (who wouldn't want some blingy chrome revolver wheels on their wagon). So, how much backspacing can I go? From what I can measure on the oem 15x4.5s, it seems like there is about 3.5" of backspacing (a bit of positive offset). The white wagon rims currently on it are 15x8, and with about the same 3.5" backspacing (but a bit of negative offset due to the wider rim), they stick out too far past the fender for my aesthetic tastes, and the current 225 (9") wide tires seem to stick out too far. Going to a narrower rim will help some (I definitely don't need an 8" wide rim), but it also seems like I need to increase the backspacing so the rim sits further in - hopefully tucked more inside the fender. How much backspacing can I go? As long as the wheel has clearance around the brakes, from the knuckle-steering linkage connections, and the tire doesn't rub the inside fender or frame too much or limit maximum steering angle drastically (a D25 doesn't have a lot of steering to begin with) it should be good to go? Thinking something like 16x7 with 4.5 to 5.5" of backspacing? Am I missing something?

As much as I like the idea of running oem style skinny steel wheels, the practicality is the selection of modern radial tires that will fit on a 15x4.5" rim is pretty limited and not very tall. I haven't given up on finding a set of 16x5.5 oem style wheels, with the idea of running a 215/85/16 (30.5x8.5) tires. But an aftermarket 16x6 or 7 would allow for more tire options, and possible up-step in tire size if desired later (with suspension etc) such a 235/85/16 (probably my dream tire size).

This is kind of the look I am going for:

 

Try again...see if it works now

 

These rims could be interesting....kind of chromed versions of the oem style...but pricey!
16x6 Hot Rod Steel | 5x5, 5x5 1/2" bolt | 3.75" backspace | Chrome finish

 

Here are similar rims to what I ran on my cj7 - always like this look. It might work on a wagon. 16x7 5on5.5 but slight negative offset.
ULTRA MOTORSPORTS 062 - Ultra Wheel

And these I like better for the larger hole revolver pattern, but 16x8 is the narrowest rim:
ULTRA MOTORSPORTS 164 - Ultra Wheel

 

The wheels on my wagon are 16 x 5". They are probably truck rims, I imagine the wagon had 4.5" originally. Tires are 235/85 and to me they fit perfect, just enough room in the wheel well.

 

yup...I like the round rear wheel wells as well. Unfortunately mine has the squared off ones.

 

Doug - have you had any luck finding usable wheels? 16x6 with 5x5.5 pattern and 4.25" center bore is pretty much impossible - I have found a couple of 16x7 options, but even a few of those have vaporized as the retailer listed them, but when go to order them, they are no longer available....I am thinking of running a 16x4.5 replacement (often identified as the Omix 16x5.5) or a set of of m38a1 rims and just stuffing the 215 or 235s on the skinny rims....

 

Yes...there are some options that are designed to fit over ford hubs at just under 4inches. Been wonder about getting those bores machined out a bit.