Just to throw in another perspective.
I have 345-30-19's on the back of my narrow body Pantera.
I can lower my car to the 11.2 compressed shock length very easily as I have air suspension. I wouldn't drive it that low but is does lower to that height without damage to the car.
The tires WILL rub slightly at that height but it is only there for car shows. I doubt you can compress your suspension to 11.2 with 550lb springs, even hitting the largest pothole available.
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