Tips I've come up with to help ensure fit when buying new wheels, tires, or both when going larger than stock size:

1) Measure factory rim backspacing (sometimes it is written in the casting on the back of the wheel)

2) Write down current tire size from tire sidewall listed in this order: mm width / aspect ratio percent - rim diameter

3) Calculate tire dimensions:

a) Tire width in inches = mm size devided by 25.4
Example: 225/75-16 is 225mm / 25.4mm/inch= 8.858" width.

b) Tire sidewall height = width in inches multipleid by appect ratio percent (add decimal in front)
Example: 8.858 * .75 = 6.644" sidewall height

c) Tire total diameter = sidewall height multiplied times 2 then add rim diameter
Example: 6.644" * 2 = 13.287; 13.287" + 16" = 29.287" total tire diameter

4) Measure what room you have greater than your current tire at any point that may rub(pinch weld, rock guard, swaybar, frame, etc). Remember if you have 1" of clearance until rubbing your current tire at the closest interference point that may rub, you can go roughly 2" wider on your tire due to tire width being centered on rim. Also note that if you go a larger width and height your side clearance will be reduced due to the larger diameter putting the tire rub point further out. Make sure you account for new rim backspacing in this calculation as well. If your rim is further out or in, so is your tire.

5) Once you have a basic understanding of what extra tire room you have you may want to add in a safty margin for tire flex in a turn, suspension movement, etc. With my lift, long travel shocks, and swaybar removed I can stuff my entire 225/75-16 tire high enough into tire well in the rear to rub on the inside of tire against the black inner wheel well. Some rubbing is OK at extreme max flex of suspension because you will only achieve this when going over huge obsticles at a SLOW speed which will not damage anything. A good plan is to CAREFULLY drive one rear tire rear of jeep up a ramp achieve max flex and measure clearance. This can be done with or without rear swaybar on (without allows more travel), but be sure you are CAREFUL and do not allow vehicle to tip, etc. If your current size allows rubbing at max flex w/o rear swaybar, you may want to install rear swaybar if you want wider tires and less suspension travel (for primarily mud, snow vehicles). If you want the flex (for maximum traction with extreme differing terrain such as boulder crawling, large dips, etc) then measure w/o swaybar and be careful on tire height and width you choose.

FOR THOSE OF YOU THAT HAVE ALREADY BOUGHT NEW WHEELS KEEP IN MIND THEY MAKE SPACERS TO PUSH WHEELS OUT MORE FOR MORE IF THE CURRENT OFFSET IS RUBBING ON INSIDE.

I am buying tires this winter and this is what I have always done on my vehicles for max tire size. This works for performance tires on cars also. I will let you all know what I think I can fit and take pics of my measurements at full flex, etc with my factory wheels for a reference for you all so hopefully NO ONE will accidentally buy too large of a tire or wrong wheel offset again.

Good luck on choosing your tire size combinations and maximizing your jeeps tire well room!

- Mark

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Previous-05 CRD KJ;Current-2010 Taurus SHO Twin Turbo (450HP), 2014 Subaru Forester Turbo (stock)

on Kap's width calculation - remember that number is the section width - the widest part of the tire - that's the industry standard - but the part that rubs is the tread not the section.
The tread width can easily vary 1/2" or more for the same section width based on the manufacturer and the tread design.
Many manufacturers do not list a tread width although it is becoming more common. If it's not listed - measure it - it's a good comparison number.

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2005 CRD
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