I recently ditched my OEM 20's in lieu of a set of 18" Gear Blackjacks wrapped with 275/70-18 Fierce Attitude M/T's. I don't want to buy a 5th Gear/Fierce combo if I don't have to, but for the life of me, I can't seem to find an equivalent 18" steel wheel. I'd rather use an 18" spare because it makes finding a spare tire a lot easier. Can I go with a 17"? If so, how do I find out what 17" tire will be the same OD as my 18". Anybody else go through this when they went to 18's?

 

If the tire diameter is close to each other then it will be fine. Your tire diameter is 33" tall so you just gotta find a 33" or close tire size for a 17" rim - 275/75/17 for example.

 

Use the caluclation method given in THIS wheel and Tire thread.

 

Thanks fellas. Dog, I read through that thread but the thing I couldn't find was whether or not my spare could be a different OD than the rest of my tires. I know that if it is, it can't be by much...especially on a 4x4. Is there an allowable percentage that I should follow? Keep in mind that my Fierce's have about 8K on them so should I go with a 17" tire that's slightly smaller? If I buy a used wheel/tire off of ebay or craigslist, should I account for wear on the spare? In other words, how much size difference will be safe? 295-70/17 is + 0.31...safe? Would you be comfortable with it?

 

I found a 20" OEM spare with a "new" 275/60/20 tire. According to the tire size calculator, this will have a diameter difference of -0.5%. Best part is, he only wants $50. Would this work for front & rear? 2WD only?

Given the history of rear end problems on these trucks, my obvious concern is rear diff problems.

 

I run a full time staggered setup and my rear tire OD is almost 1" lower but wider than my front tires. No ABS or other issues here for a 2WD.
Front - 275/55/17
Rear - 305/45/18

 

I don't think front/rear would be a problem unless I put it in 4WD, which I wouldn't with a mismatched spare, I'm just worried about left/right.

 

If you can't find a used 18" wheel, I know places will put the Cragar Soft 8's on sale in black for around $65 once in a while. It's a GOOD, STRONG steel wheel, a long time favorite of the Jeep crowd and then you'll have the 18" like the rest of them and won't have to worry about any conversions or slight diameter difference issues...


EDIT: Nevermind, I can't find it any larger than a 17x9...

 

I used my 8 year old factory 31" spare (265/70/17) on the rear pass side for 40 miles to get a new replacement tire and had no issues. The other 3 corners were 28". I was more concerned about the spare rubbing my inside fender since i have a 6" rear drop.

 

I shoulda just went with 17" wheels.