I drive a 2007 Colorado z85 4x4.... i bought a 3.5" rox tb leveling kit with 2.5" rear shackles, pro comp shocks, and 15x8 pro comp wheels..... would i be able to fit a 33 12.50 15 or would i be better off with a 32 11.50???
33's won't fit without a bunch of cutting or a lot of cranking. I am running 32's on Suspension Maxx Keys and shackles. I had to trim the rear of my front fender wells and my flare due to the backspace on my wheels. Before, I had the 32's on stock wheels and in any compressed situation while turning they rubbed the sway bar.
A 3.5 inch torsion bar lift will ride like crap. You will need to flip upper ball joints to prevent bind and lower front differential to correct cv axle angles as well. Also the upper control arm is probably going to be smacking against metal because there is little to no downward travel left with that much crank and the kit probably doesn't have bump stops. Personally I wouldn't lift 3.5 inches with the torsion bars. I would lift a little less and go with 32 or 33 x 10.5 wide
32's will be a lot better for mileage/economy than 33's will be.
I drive a Z85 with 31.7' and my mileage is barely 15 mixed driving. 20-21 highway if I drive easily.
The shift points are pretty screwed up, OD has no torque when on the low end, like 40-60mph. With 33's, it will be worse yet.
I think my tires are 9.6% larger than stock. That means the speedometer is off by 9.6% at all speeds too. 33's of course are even more inaccurate on a Z85 computer.
Greg makes great points about the torsion bar cranking. I think that is too extreme.
When you lift your truck.....with the truck parked on level ground, measure the distance from the center of your front hub vertically to the bottom of the fender lip. Stop at a 24.5 measurement. My Z85 only let met go to just over 24". I'm not at 24" or a little less. I've flipped my ball joint and added a spacer. That allowed me enough clearance to hit 24" without doing damage. But the ride is pretty bad. I can't hold a straight line on rough roads, and hitting a rough patch in a curve is pretty scary since I end up skipping in the direction of the body roll.