What is the biggest size tire I can fit with no lift on a Jeep Wrangler JK?

Chris

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One of the most frequently asked questions on this forum is “What's the largest tire I can fit on my stock / unlifted 2007+ Jeep Wrangler JK?”. So, I put this post together so that we can link to whenever this question arises.

First things first, Jeeps come stock with three different tire sizes:
  1. 225/75/16 (29”x9”)
  2. 255/75/17 (32”x10”)
  3. 255/70/18 (32”x10”).
The backspacing on stock JK wheels is 6.25". That means that the mounting surface of the wheel is 6.25” from the rear lip of the wheel. The larger the backspace number, the further under the fender (and closer to suspension components and airdam) the wheel will be (see below image).

40-RWD-Wheel-diagram.jpg


I see posts all the time saying that a 33” tire will fit the stock JK just fine, and that is semi-true. In reality, this question requires a 2 part answer. The first part deals with tire diameter. The second part deals with width.

It is true that the largest diameter tire you can fit on a stock JK without issue (read on) is 33” in diameter. With this diameter, you shouldn’t have any issues on the street. However, you could get some contact with your fenders if you flex offroad. Disconnecting your front sway bar will cause contact with your fenders.

Now let’s take a look at tire width. People often overlook this aspect when choosing a tire. The width on most 33's range from 10” – 12.5”+.


On Stock Wheels
The largest tire you can fit without a chance of problems on road is a 33x10 tire (also called a “pizza cutter”). An example is the 255/80/17 BFG KM2. Because this tire is the same width as most stock JK tires, there is no issue on road, despite the larger diameter. You can run this size without issue.

Now, let’s consider some tires that could potentially cause slight issues on road; the 33x11s. The common sizes of these would be 285/75/16, 285/70/17, and 275/70/18.

The 275/70/18 measures slightly under 11” wide, while the other two measure a little over. Many folks have reported running these sizes without issue. However, others have experienced contact with the airdam or front suspension components. Simple fixes are to add washers to the steering stops, trim the airdam, or install wheel spacers.

Any tire larger than 11” in width, you are almost guaranteed to have to do one of the above mentioned mods. In fact, if you go too much wider than the 11” tire on stock wheels, you stand a good chance of making contact with your rear swaybar end link. If that is the case, wheel spacers can correct this issue. Common sizes are 295/70/17 (33x11.6), 305/60/17 (33x12), 305/70/16 (33x12), 295/65/18 (33x11.6).


On Aftermarket Wheels
As I mentioned initially, the stock wheels have a backspacing of 6.25”. This is too deep of a backspace to allow proper clearance for a decently wide tire. The general consensus is that the “magic number” for backspacing for the JK is 4.5” or less. It does not mean you can't run a wheel with 4.6”+. But 4.5” and under is the safest bet.

Many 15” wheels have less (sometimes a lot less) than 4.5”. That's so the wheel clears the brake calipers. Most 15” wheels come with 3.75” of backspacing (MB72, MB TKO, etc). There are a few that come with more (such as the Black Rock 909 – 4”) and some that come with less (such as the Level 8 Tracker – 3.32”). Just remember, the lower the backspace number, the further out the wheel will sit from the Jeep body. One of the most common wheel/tire combos on this site is the 15x8 MB 72 wheel with 33x12.5x15 Duratrac tires. Dozens of people run this setup without a single issue on the street. However, just like most of the other 33” combinations, you can get some fender contact when offroad.

Also, be aware that, while many 15" alloy wheels will fit over the Wrangler's brake calipers, most 15" steel wheels will not.

Once you get into 16”+ wheels, it's pretty easy to select a wheel with a backspace near 4.5”. The most common 33” tire to run with 16” aftermarket wheel is the 285/75/16. A common tire size for the 17” wheel is the 285/70/17.

Links of interest:
Utility to compare tire sizes
Wheel / tire fitment calculator