Stock Rubicons come with 32 inch tires. Putting on 33's would actually only cause the tire to come 1/2 inch closer to the fenders. You have to think about the distance from the axle (tire radius), not the distance across the entire tire (tire diameter). with 32 inch tires, there is 16 inches from center of axle to the edge of the tire. (that is 16 inches in the direction toward the fender) 33's have 16 1/2 inch radius. That would make them 1/2 inch closer to touching a fender ....Therefore, a 1/2 inch lift should fit 33's and a 1 inch lift should fit 34's, etc. Now if less wheel backspacing and wider tires cause the wheels to stick out where they would touch the fender flares instead of tucking behind, that would be an issue. Obviously, extended bump stops would be needed, but by my calculations, a 3 inch lift should clear 38 inch tires.
Anyone find an error in this math? It goes against what the manufacturers of the lifts are recommending. (2 inch lift for 33's, 3 inch for 35's, etc.)

 

Well, your math is correct. But when applied in the real world you get rubbing with those numbers.

 

Heck, 35's fit with no lift. Just make sure you only go straight and don't hit any bumps!

 

I've wondered about this too, and I think the answer is that your suspension does not move perfectly up and down along the plane of the hub.

It seems to me that most 35" tires are quite a bit wider than the stock 32's (mine are 13.5" wide). Now picture what happens when just one corner is under compression -- the axle will flex up so it's at an angle to the road surface (one wheel higher than the other). So if you have a wider tread by several inches, the very outside edge of the tread will be poking up farther into the fender well than it would have with the stock-width tires.

I'm guessing that lift manufacturers want to be pretty conservative when they "guarantee" that a kit will clear a particular tire size, so they probably assume the worst case. I'm guessing that if you went for very narrow 35's, you would only need about 1.5" of lift, but definitely don't quote me on that. I have never tried this.

 

The math may be OK, but the application of the mathematics to suspension travel is not. Sorry.

 

the problem is that your only thinking vertically. While you may move the suspension up a 1/2 inch the tire will expand in every direction, you have to think about clearance on the sides of the tires as well as the top.

 

I wanna see pics of your 38's on your 3" lift LOL