Barracuda spring sag in rear.
IMO, most of the suggestions here are band-aids. My recommendation is to replace the springs. Yes, it's not the cheapest option, but it is the most secure. There are plenty of vendors out there. I went to McVeigh Truck Springs for the set I put in the 73 on the recommendation of another FABO member. It solved the sagging problem and did not adversely affect ride quality.
My reservations about add-a-leaf and coil-over shocks are these. Both stiffen the rear suspension which makes the car understeer more. The coil-overs place more stress on the upper shock mount than they were designed to take which could lead to failure.
How big a tire can be mounted may depend on whether or not you move the spring inboard and how long the axle is hub-to-hub. I run 15x7 with 4ΒΌ" BS. The most I could get under the wheel wells on a 72 BBP disk brake Demon was a 235/60-15. It's very close to the outside edge of the wheel well in front and close to the spring in the back.
Exactly. Buy the right springs. Everything else is a band aid. Yes, you may do ok having the springs re-arched, but that varies with the quality of the springs. Sometimes it works very well, other times they just sag back to where they were. Take a look at getting a new set of XHD's, or go to a set of ESPO springs and specify a +1" lift. They do 2"+ also, but keep in mind your current altitude is probably lower than stock- ie, even a +1 spring will lift your car more than 1". Anything related to shocks that lifts the back end of the car is asking for broken shock mounts. The shock mounts were not intended to support the weight of the car, just the force from the shocks.
Next on the list is- buy the right
rims. Often times people jack up the back of the car to clear rims/tires that are either- 1. Too big for the stock spring location, so the tires have to hang out past the quarter and have the rear end of the car lifted, or 2. Have the wrong backspace.
Like that Demon, for example. With a 15" rim you can't do any better than 4.5" of backspace in the front, which means you're pretty well stuck with a 235. I'm kinda surprised you got anything bigger than a 225 to clear with a 4.25" backspace, it had to be close! But in the back, a 15x8" rim with 4.75" of backspace will allow you to run 275/60/15's. No problemo, been there, done that. No cutting, offsetting, or relocating necessary.
