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Old 02-28-2012, 09:59 AM   #1
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Largest tire on stock JK? Here's your answer!

One of the most frequently asked questions on this forum is “What's the largest tire I can fit on my stock/unlifted 07+ JK?”. So, I put this post together that can either be made a sticky, or something that we can link to whenever this question arises.

Have to give thanks to kbwwolf for proof-reading and making a few tweaks here and there. Thanks bro!

First things first. Jeeps come stock with 3 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)


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
Adding washers to the steering stops

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Old 02-28-2012, 11:01 AM   #2
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Awesome stuff, Jeff.

Here are a couple other things that might help:

Tire Dimensions Made Simple - Discount Tire


How to convert offset to backspace:


Take offset, divide by 25.4, then add the overall rim width (rim width +1) divided by 2

so: for a 16x8 wheel with -27 mm offset:


-27mm / 25.4 = -1.06" + (((8"+1")/2)= 4.5") = 3.43" BS


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Old 02-28-2012, 05:06 PM   #3
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Sticky vote x1
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Old 02-28-2012, 08:18 PM   #4
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Thanks, I actually think I decided to go with 18" rims, would a 275/65/18 or 285/65/18 be better for a 9" rim. I found a few rims I like, the one has a 4.5 offset but some of the others go up to a 5.5 offset. would the 5.5 offset still work with those size tires.
Thanks
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Old 02-28-2012, 08:49 PM   #5
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Originally Posted by kevprit View Post
Thanks, I actually think I decided to go with 18" rims, would a 275/65/18 or 285/65/18 be better for a 9" rim. I found a few rims I like, the one has a 4.5 offset but some of the others go up to a 5.5 offset. would the 5.5 offset still work with those size tires.
Thanks
The 275/65/18 is only a shade wider than the stock 18" Sahara and it no taller. Between those two sizes, I would definitely go with the 285/65/18, which would measure out to roughly 32.6" tall and 11.2" wide. That tire would definitely work on the 4.5" backspaced wheel. It may also work fine on the 5.5" backspaced wheel, but there is a chance you might get some rubbing up front on full turn. Simple fix would be a washer or two on the steering stops. See the bottom of the first post for a link to an article on how to do this.
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Old 02-28-2012, 08:55 PM   #6
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Thank you. Could I go any bigger of a tire then the 285/65/18 or would that be the biggest you would recommend.
Thanks,
Kevin
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Old 02-28-2012, 08:55 PM   #7
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315/75/16s with 4.5" BS and fenders cut on my stock suspension now. Minimal rubbing on Rubi rail but I will trim that. It's true. You can run 35s on stock setup if you cut. I have had them to the bumpstops.
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Old 02-28-2012, 09:06 PM   #8
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Originally Posted by kevprit View Post
Thank you. Could I go any bigger of a tire then the 285/65/18 or would that be the biggest you would recommend.
Thanks,
Kevin
A 295/65/18 on a wheel with 4.5" backspacing would be what I would shoot for. But there aren't many options out there in that tire size. I don't know a whole lot about 18" tire options though.

Quote:
Originally Posted by Sparkplugg View Post
315/75/16s with 4.5" BS and fenders cut on my stock suspension now. Minimal rubbing on Rubi rail but I will trim that. It's true. You can run 35s on stock setup if you cut. I have had them to the bumpstops.
It can be done, yes. But, like you said, there will definitely be some cutting and clearancing involved. This thread is more focused on the person who just wants to put the largest tire possible on their stock setup. The majority of those folks will not want to go with flatties or cut stockers. Hell, with the Metal Cloak fenders, they claim you can run 37s on stock suspension!

On a side note, one of these days I myself plan to go with 315/75/16s with BW flats and my TF leveling kit.
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Old 02-28-2012, 10:04 PM   #9
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ok last question. Would a 275/70/18 work and look nice? and what is the size difference between that and the 285/65/18. there are no tires available for 295/65/18, So I was going to go with 285/65/18 but there still arent very many tires available. Thanks.
Kevin
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Old 02-28-2012, 10:59 PM   #10
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I was talking about it in my revived thread but I'll add the question here. Is there an easy way to figure out what diameter will or will not rub the fenders off-road disco'd? I've been getting the impression that pretty much anything over a stock diameter will which means all those Rubi's out there with the e-disco's and 32.1" tires have got to really be cutting it close, and any Sport with 17" option or Sahara with quick discos. My ideal tire would be a 285/75/16 on proper 4.5" backspacing but it sounds like that extra .7" diameter (.35" radius) combined with the 15mm extra width on each side and proper backspacing would cause it to cut into the fender.
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Old 02-29-2012, 06:12 AM   #11
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Originally Posted by kevprit View Post
ok last question. Would a 275/70/18 work and look nice? and what is the size difference between that and the 285/65/18. there are no tires available for 295/65/18, So I was going to go with 285/65/18 but there still arent very many tires available. Thanks.
Kevin
Actually, one of the best AT tires out there is available in the 296/65/18, the Goodyear Duratrac.
A 275/70/18 would work. That would spec out to 33.2"x10.8". That would be a full inch taller and .8" wider than stock.

Quote:
Originally Posted by flyinion View Post
I was talking about it in my revived thread but I'll add the question here. Is there an easy way to figure out what diameter will or will not rub the fenders off-road disco'd? I've been getting the impression that pretty much anything over a stock diameter will which means all those Rubi's out there with the e-disco's and 32.1" tires have got to really be cutting it close, and any Sport with 17" option or Sahara with quick discos. My ideal tire would be a 285/75/16 on proper 4.5" backspacing but it sounds like that extra .7" diameter (.35" radius) combined with the 15mm extra width on each side and proper backspacing would cause it to cut into the fender.
There is no formula that I am aware of. To gain that extra clearance, you could go with 18/59 or 19/60 stock coils. That could yield you a little bit of lift. Of course, you would need to check to see if you already have these springs. Another option would be the Teraflex leveling kit (either spacer or coil). That will give you 2" in the front and 1" in the rear.

Here is a thread over at JK-F that you may find useful.
33" stock height. rubbing on swaybar links when disconnected
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Old 02-29-2012, 08:10 AM   #12
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Originally Posted by kjeeper10 View Post
Sticky vote x1
x2 on the sticky.

This is now my go-to link for any "Biggest tires, no lift" questions.
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Old 02-29-2012, 09:10 AM   #13
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Old 02-29-2012, 02:25 PM   #14
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There is no formula that I am aware of. To gain that extra clearance, you could go with 18/59 or 19/60 stock coils. That could yield you a little bit of lift. Of course, you would need to check to see if you already have these springs. Another option would be the Teraflex leveling kit (either spacer or coil). That will give you 2" in the front and 1" in the rear.

Here is a thread over at JK-F that you may find useful.
33" stock height. rubbing on swaybar links when disconnected
Thanks I'll check that thread out. Yeah I need to figure out how to check the coils. I've heard they put heavier duty coils on JKU's and on JK/JKU's with the factory towing packages and I do have the Max Tow package on my JKU. We're installing my disco's on Sunday and going to test the articulation and see if we can figure out how much room I have to work with.
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Old 02-29-2012, 02:34 PM   #15
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Yeah I need to figure out how to check the coils. I've heard they put heavier duty coils on JKU's and on JK/JKU's with the factory towing packages and I do have the Max Tow package on my JKU.
To check your coils, simply look for the tag attached to the top of them. Check all four, since sometimes the two fronts are different spring rates.

Here's a photo of the tag. The last two #'s on the tag give the spring rate (in this case 16).

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Old 03-01-2012, 09:20 PM   #16
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i just got a 15x8 rim and was wondering what is an equivalent size to 33" tires by 12.5 or 10 thank you
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Old 03-01-2012, 09:32 PM   #17
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i just got a 15x8 rim and was wondering what is an equivalent size to 33" tires by 12.5 or 10 thank you
Um, a 33x12.5x15.
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Old 03-01-2012, 09:58 PM   #18
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ya but what would that convert over to so i can search all the tires that are like that
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Old 03-01-2012, 10:13 PM   #19
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ya but what would that convert over to so i can search all the tires that are like that
A 33x12.5x15 would be something like 315/70-75/15. Not sure you are going to find anything like that. For the 15" rim, it is best to just go with a 33x12.5x15 tire (as long as your wheel has appropriate backspacing to support it). Plenty of options out there.
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Old 03-01-2012, 10:15 PM   #20
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ok thank you
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Old 03-02-2012, 10:59 AM   #21
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x2 on the sticky.

This is now my go-to link for any "Biggest tires, no lift" questions.
Yeah...good stuff here
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Old 03-05-2012, 09:01 AM   #22
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sticky vote YES!!!

Data input: I searched far & wide for "biggest tire" possible to stuff on the stock 18" 08JK configuration.

My long-time tire shop determined 275/65/18 for the Kelly TRS was maximum without lift/different rims.

They have proven to be wonderful for my use as DD and general rain/mud/mountain pass snow/ice.

The front bump stop had to be screwed out about 1/4" to keep clear of any contact at full turn L or R.

Despite the circumference being "the same" as stock Duelers, I have dropped about 1.5 mpg and the auto tranny spends less time in OD.

While stock my 3.73 diffs would run 55-60mph at about 1800 rpm, and known roads with slight up/down sections, could cruise without downshift. With the extra rubber those same slight rises always provoke downshift. And many places I simply turn OD off due to the wandering shift pattern.

It appears to me, there is a crucial rolling resistance at the normal highway speed, that is changed by the subtle tire change. While I doubt the added weight is responsible, the results I've had suggest you can't have maximum mpg [not that most here are expecting that] and maximum traction at the same time.
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Old 03-07-2012, 09:14 PM   #23
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sticky!!!
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Old 03-08-2012, 11:07 AM   #24
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Wheel/Tire combination

For tires I went with the Nitto 35" 12.50 17 Trail Grappler, this is the best allround tire that meets what I want out of my tires: Good on the trail, good in the mud, good at climbing, good on snow and ice. Like I said best tire.
For wheels I went with Level 8 Strike 5 17" 12.50.
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Old 03-14-2012, 06:41 AM   #25
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Why exactly is it called a "pizza cutter"
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Old 03-14-2012, 07:29 AM   #26
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Why exactly is it called a "pizza cutter"
Cause they are tall and skinny, like a pizza cutter.
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Old 03-15-2012, 03:44 PM   #27
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My '11 Sahara has 255/70/18 tires on it. I'd like to go with a tire that is 275/70/18.

I don't have a lift and don't really want to get one. Will these be OK? Does anyone have these on their Jeep without a lift or spacers?

Thanks!
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Old 03-15-2012, 04:51 PM   #28
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My '11 Sahara has 255/70/18 tires on it. I'd like to go with a tire that is 275/70/18.

I don't have a lift and don't really want to get one. Will these be OK? Does anyone have these on their Jeep without a lift or spacers?

Thanks!
Lol...did you read the first post in this thread?

That size would be a 33" tall tire, just under 11" wide. It'll rub your fenders off-road (but would be okay on-road). And it's probably too wide to use with your stock rims. It might rub your air dam or wheel stops.
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Old 03-15-2012, 04:59 PM   #29
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still working on $$ for 33" upgrade....
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Old 03-16-2012, 06:40 PM   #30
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awesome information, it is like going to a Jeep Wrangler 101 Class.. except it's FREE!

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