Suspension/Wheel Offset

I am re-building my dad's 1971 AMC Javelin AMX. The car sat for 20 years in a driveway uncovered. The car currently sits on 265/50/15 all around. I'd like to switch to a square 275/40/17. I'd also like to purchase the ControlFreaks Independent Front Suspension (I'm not sure if this changes the equation). How would I figure out offset to ensure no rubbing?

I would get the car on ramps or blocks so that the suspension has weight on it and you can get under the car. Get under the car and check for clearance with the current setup that you have. Check inside and outside, front and back clearance in all wheel wells, and take notes. Turn the front wheels and take more measurements.

Now remove one of the wheels from the car and document the setup. Tire height, tire width, and measure backspacing on the wheel. Put a piece of masking tape across the back of the rim and measure the distance from the tape to the mounting flange, this is your backspace. You can also put tape on the front edge and measure to the mounting flange, this is your 'front spacing'. Google 'how to figure out wheel offset' and use the measurements that you have to understand what the offset is on the existing wheels.

Compare the existing tire width and diameter to your proposed new tires, and look at the clearances that you have between the tire and body. Change the offset, if required, to balance out the clearance available.

For example, if you have 3/4" clearance between the rear fender lip and tire, and 1" between the inner fender and tire. If your new tire is 1" wider than the existing, then you would have 1/4" clearance on the outside and 1/2" clearance on the inside, assuming that the wheel offset/backspace remained the same.