You can put 33'' tires on without any lift.But if the tire goes any wider than the stock size,you have to change a new rim,or put some wheel spacers on.
For the stock rim with 6.25'' backspacing, some jk owners claim even the 255/70/18 stock tires will rub the brake line when at a full turn.
here is some q&a about jk wheel and tire.
Q: What is the biggest size tire I can fit on my stock Jeep JK Wrangler?
A: The largest tire size that the factory recommends is a 255/75R17 (which comes standard on Rubicon models) or a 32x10.50. However, there are many Jeep JK Wrangler owners who are currently running as big as 285/70R17 or 33x10.50's with little to no rubbing issues.
Q: What is the biggest size tire that I can I fit with a 2.5" Budget Boost?
A: 33" without any problems and 35" tires with only minor rubbing at a full flex. Depending on how wide your tires are, you may experience some rubbing at a full turn especially if you did not install an adjustable front track bar and/or are still running factory wheels which have 6.25" of back spacing.
Q: What is the biggest size tire that I can fit with a 3" lift?
A: 35" tires and depending on what lift kit you have, you may still experience some minor rubbing up front at a full flex and when turning.
Q: What is the biggest size tire that I can fit with a 4" Lift?
A: 37" tires but you will need to trim the rear corner of the rocker pinch seam and you may still experience some minor rubbing at a full flex.
Q: Will 15" Wheels Fit on my JK?
A: Most steel ones will fit without any problems and depending on the thickness of the wheel most aluminum ones will as well. The only thing you really need to make sure is that the wheel clears the brake calipers.
http://www.jk-forum.com/showthread.php?t=17449Q: What back spacing will I need on my wheels in order to clear 12.50 wide tires?
A: I would recommend that you do not exceed 4.75" of back spacing and even at that, you may still have some minor rubbing up front at a full turn. Also, I would recommend that you do not go any less than 3.75" as anything less would cause your tires to stick out very far past the fender flares. Any back spacing within this range should work out great.
Q: What is backspacing?
A: The distance measuered from the mounting surface of your wheel to the outside edge of the rim - see diagram below.
Q: What are wheel spacers?
A: Wheel spacers are rings measuring 1.25"~1.5" thick, are typically made out of billet aluminum and are designed to be sandwiched in between your Jeep's axles and wheels. By installing wheel spacers, you will effectively reduce the amount of back spacing your wheels have allowing you to install wider than stock tires without having to replace your factory wheels.
Q: Are wheel spacers safe to use or do they cause extra stress on your axle or wheel bearings?
A: High quality wheelspacers, the kind that bolt up to your axle first are no more dangerous or cause any more stress to your axles then would a wheel with less backspacing. Anyone who tries to tell you otherwise doesn't know what they're talking about and I have yet to hear a single good or specific explanation as to exactly how they are worse. Just to be clear, the cheap-o spacers (the kind that you can get at PepBoys and are sandwiched between your wheel and axle using the existing wheel studs) are in fact EXTREMELY DANGEROUS. These cheap-o spacers leave little thread for your lug nuts to hold onto and can fail. DO NOT USE THESE!
Q: On the road, what PSI should I be running in my tires?
A: For optimal comfort and even tire wear. you should not run the recommended PSI listed on the sidewalls of your tires. Typically this will be way too much. On average for a 33" tire, I would recommend that you run your tires at approximately 28-30 PSI. For a 35" tire, I would recommend running approximately 26-28 PSI. For a 37" tire, I would recommend approximately 24-26 PSI.
Q: On the trail, how much should I air my tires down to?
A: Typically, I recommend that people air the tires down to about 10~15 psi.
Q: What are all the factory wheels that are available for the JK?
A:Factory wheel type and sizes listed below:
X Standard
Painted Steel - Size 16 x 7.0
X Optional
Painted Cast-Aluminum - Size 16 x 7.0 (2007)
Painted Cast-Aluminum - Size 17 x 7.5 (2008)
Sahara Standard
Painted Cast-Aluminum - Size 17 x 7.5
Sahara Optional
Painted Cast-Aluminum - Size 18 x 7.5
Rubicon Standard
Machined Cast-Aluminum - Size 17 x 7.5
Backspacing on all factory wheels is 6.25"
Q: Will a 33" tire fit on the factory spare tire mount without causing any warping or damage to the tailgate or mount?
A: You should be just fine with a 33" spare tire especially if the sidewalls of it is making good contact with the rubber isolators on the tailgate. The isolators will help prevent the jiggling of the tire and that is ultimately what will cause you problems down the road.
Q: What size are the lugs nuts used and what socket will I need to remove/install them?
A: The lug nuts you will need are 1/2"-20RH and you will need a 3/4" or 19mm socket to remove/install them.
Q: How many foot pounds should I tighten my lug nuts to?
A: You should tighten your lug nuts to 95 ft. lbs. of torque.
Q: Is there any advantages to running a larger rim size vs. a smaller size?
A: Yes, a larger rim size will reduce tire sidewall flexing and this will provide better handling on pavement. On the trail, less sidewall flex can also help to make your Jeep feel more stable on off camber situations.
Q: Are all rims the same or is there a certain type of rim for offroading?
A: So long as you can mount your tire on it, a rim is pretty much a rim. Some Jeepers prefer to run steel wheels as they are typically much more affordable, are easy to touch up and will bend as oppsed to breaking but, they also tend to be heavier than aluminum. The one thing I would recommend is that you try and get a rim that is about 8" in width. The narrower width will help keep your tires from loosing a bead when aired down for the trail.
Q: How do you determine what size tire will fit what size rim correctly?
A: Typically, most off road tires come in a 12.50" width and for the most part, a 10" wide rim is what you would want. However, unless you are running beadlocks, I would recommend that you select a wheel that is 8" in width or there abouts. When aired down for the trail, the narrower width will help prevent your tires from loosing a bead.
Topic: wha tire size for stock sahara unlimited (Read 3856 times)