Take a wheel off, preferably on a cement garage floor and leave the car on a jack stand. Using a plumb line on the face of the hub that the rim touches and let it drop to the floor. Put a chalk mark on the floor directly below the hub face. Check the contour of your wheel tubs for verticle movement of the wheel with an idea of how tall you want the wheels. You should have a ton of wheel tub behind there, they're probably high and deep with a fairly flat top. Drop a plumb line from the outer edge of the leaf spring to the floor and make another chalk mark on the floor directly below the outer edge of the leaf spring. Measure from the first mark to the second and this will be your total distance before the wheel rubs on the spring. Remember to keep in mind the height of the tire as it may touch the inside of the wheel tub when the axle move up severely. Subtract the amount of clearance you want to the spring (or inner tub ) and this is your total offset. You will find that this is a huge offset and not every manufacturer offers rims with every offset a person wants. My rear tires are 10 1/2 inches wide at the tread and I still have almost two inches before the tires contact the springs. The tubs on my car are almost verticle at the inner panel so they are not of concern. I believe my offset is around 5 1/2 inches and I can still remove the wheels providing I jack the car on the frame rail. The clearance at the wheel opening is 1 inch between the tire and the fender wheel lip.
