Originally Posted by jchammond

I just use a custom wheel backspacing chart & then perform the math for the Front spacing(hub face to outer wheel lip)...having the actual dimensions on tires do help to some degree,,,as they will actually grow in diameter after mount & inflation...some printed specs on tire rack & other sights are correct & some are off a bit.
That calculator you have is very thorough with showing actual bulge of tires pending the section measurements are correct & also account for caliper clearance.
I use a transmission speed/gear ratio calculator for speedometer accuracy & by how it affects gear ratio.
Most of my general experience is from actual hands on with different size wheel/tire combos.
Lots will fit under the Huge Z fender wells,,,it's just how the owner prefer's his/her look