An old thread indeed, but still relevant. My note is to be sure folks are aware that wheels are 1" wider than their listed size. So for example, a 17x9 wheel is physically 10" wide, and 9" across the tire bead seats. This is mostly important when combined with backspace. As the wheel is actually 10" wide, a zero offset would be 5" backspace - not 4.5". Just a reminder to throw that into your calculations.
One more tip. Any tire and wheel combo that will fit (whatever is on there now) can give you a basis for measuring clearances with larger wheels and tires. Simply draw-up your current wheel and the tire as listed in tire spec's, then measure your clearances to all nearest points at any suspension travel and turning for fronts. Use the closest points to determine clearance and give yourself a bit of wiggle room. Write these clearances on your drawing where you measured.
To choose your tires and wheels, look-up the specs for a tire that will fit in those clearances, with a bit of their own clearance. So for example, your current rear wheel and tire have exactly 3" clearance to anything inboard, and 2" to anything outboard. That's 5 inches of room. Let's say we want a minimum of 1/2" clearance on each side for safety (1" total). Your new tire can be 3 + 2 - 1 = 4 inches wider. Be sure to check clearance at any new height based on larger diameter as well. But, it won't fit unless you center the extra width, so your new wheel will have to sit 1/2" further inboard, meaning you need 1/2" more backspace to get it there.
Don't overlook custom offset wheels or DIY wheel shells and rims to get the max tire with perfect clearances.