very good point
Im going to measure today, but We Have a bit of the chicken and the egg sinerio. I have 2 option with wheels. Buy something off the self, or custom order a set of wheels. Last build I did I ordered custom Budnick wheels, measured thoughly and they fit well, very expensive. Wheels and tires were over $4,000 on that build: budnick wheels and michelen pilot supersport tires (that was 10 years ago costs.) Already had a killer rear end.
On this Car, It needs a rear end. Where I need to have a custom rear end built, It seem most economical to at least see if I can find a wheel off the shelf that would fit the project. The wheels I think would compliment the car have a backset of 4.75 and 4.5 in the rear. I prefer the 4.75 wheel. 4.75 sounds a bit much for a stock rear end, but I could have them bump the rearend just .25 of an inch to get them to fit. I find value in stick with the factory rear end dims, but if Im able to get a wheel package for half the price of custom wheels thats $2,000 savings
Im considering adding that 1/4" to either side of the rear. now that does also seem like : If i just order longer lugs, I could use a 1/4" wheel spacer, but that seem like poor planning?
so... here's what *I* would do
(full caveat: i am actually three raccoons in a trench coat)
start with what is known and then extrapolate from there.
you (likely) have a 7.25 in there now, so that dimension is knowable. now you can compare that to these data points in this thread:
Ok, so, I've posted parts of this list a few times, normally in response to some of the really inaccurate charts and lists that are out there and posted too frequently. It's not my list, I sourced it from the internet but I can't remember where. Since the time I downloaded it several years ago, I have personally confirmed a bunch of these numbers. The A-body numbers, the E-body numbers, several of the B-body measurements, a couple of the C-body measurements, and even the D100 measurements. They've all been spot on, so I have no reason to suspect any of the measurements I haven't personally...
then, with that information, and the specs from the disc kit and moser you can calculate what your wheel mounting surface is. so that's one critical. in the same hand, you'll know where the spring lands-- this is a fixed point, so an easy calc.
the next would be setting up your dummy axle to the ride height(s) you think you'd like to be at-- so you'll need the rim size, but more importantly the tire size
from the manufacturer because not all same size tires are the same size, ya dig?
so now you have your ride height, your WMS and where the spring is-- from there with the rim specs you can see if or how far you need to move the spring, and thus the perches on the axle housing, along with an idea of the area that the rim and tire takes up. this should give you a fairly good idea and decent picture of how everything is going to fit and where possible points of contact are.
don't forget to account for suspension movement. not only vertically but also
horizontally. hard cornering can lead to shifting the axle ever so slightly and rubbing the wells and or frame/springs.
i understand a lot of this is abstract and a pain with the physical moving and positioning of heavy components, but that's the price of admission for running on the ragged edge rim/tire wise.
full disclaimer: it's early and i'm not fully caffeinated-ed yet, and as mentioned i am also three raccoons, so i probably missed something in there. but you get the overall idea of the thing with the stuffs.