Whether you are new to wheeling, or you've just gotten a new-to-you Jeep, we've all wondered at some point about the biggest tires that would fit under our Jeep. Despite knowing a whole lot about this addiction we call Jeeping, we've recently added to our Jeep stables. Now we're right back at the beginning, so to speak.
There are a lot of factors that figure into this. Wheel backspacing and rim width for particular tires are important to consider. Read the manufacturer's specs of the tire you are contemplating because they specify it for a set rim size. Skinnier rims mean more sidewall bulge, which might cause interference. Wider rims will equate to less sidewall bulge, but might mean the tire will hit on the fender, or you won't be able to air down as far. More backspacing means you might hit suspension components, and less often means that you'll interfere with your fenders.
We all use our Jeeps lovingly (read: abuse them). Due to frame tweakage or spring sag (or just maybe the bevy of women you are toting in the back of your Jeep), all the circumstances will be different, and will play a big part in what hits. This is a basic guideline for what you can run on your Jeep, but if you aren't sure try to find people with a similar Jeep and ask them about tire sizes.
No one has put together a table of sizes for all Jeeps like we have here. Sure, we skipped the M-726, M-170, M-678, CJ-4, and CJ-10A. But just how often do you see one of them? Some models we don't feel are safe or stable with the stock-width axles and wheelbase above a certain lift or tire size, and some we don't feel have the power to turn the bigger tires. If you are swapping any of the major drivetrain components, use this as a reference and go from there. Keep in mind the tire sizes are actual sizes, so use the P-Metric sidebar in this article for a reference to your tire size if you've got a metric tire. If you've got a standard-size tire, subtract an inch from the advertised size on the sidewall. As usual, the best bet is to actually measure the tire in question.
A stock flattie on stock rims can clear 30x9.5, but add a set of 15x8s to the mix with 3 - 3 1/2 inches of backspacing and you can clear 31x10.5s with rare instances of rubbing. The wider tires will tend to rub on the springs unless you run with very little backspacing. Overall, with an otherwise stock flattie (engine, transmission, and transfer case) we'd put 31s on it and run it like that for the nostalgia factor.
Early CJ-5s and CJ-6s
These can clear 30x9.5 tire with no problems, stock rims or not. A 31x10.5 can clear with the stock rims, but up front they'll hit the springs at full turn and the top of the tire will tag the inner fender when articulating. You can also put a set of rims on with less backspacing and you can clear the springs up front, but they might contact the fenders in the rear. Again, with a stock drivetrain, we'd put 31s on it and trim wherever needed.
The later CJs with their larger engines and slightly larger wheel openings, as well as wider axles changed things a bit. 31s are possible on stock rims and it just goes up from there. While you can run 40s on all of them, we'd only feel OK with them on a Wide-Trac CJ-8 (and only then if we liked replacing axle shafts). Anything else would be very scary.
Smaller stock tires come standard because of YJ's lower stance. With a set of 30x9.5s on the stock rims, you will self-clearance the fender flares. Ditch them and add TJ flares for the ability to put 31s on it if your springs aren't sagging a whole lot. For anything wider than a 10 1/2-inch tire, you'll want aftermarket rims with 3 1/2 inches of backspacing. Stock rims with wide tires will have you hitting your springs at every turn. We'd put 33s on it with a 4-inch lift and TJ flares, then call it done.
TJ Wrangler and LJ Wrangler Unlimited
With 31-inch tires out of the factory, they obviously fit. Add a 1-inch body lift, and 32s will just squeeze under there on the stock rims. But keep them to 9 1/2- or 10 1/2-inches wide. Like the YJ, with anything wider than 10 1/2 inches on the stock rims, there will be contact with the suspension components. With a TJ, we'd put 33x12.5s on 15x8-inch rims with 3 1/2 inches of backspacing. On the LJ, we'd go to 35s and keep the rest of the recipe the same.
The 235/75R15 isn't that hard to translate into a normal usable number. The width is 235, the aspect ratio is 75, and R15 is the diameter of the rim. To use that when shopping for tires, use these two formulas:
Actual Height (in inches) = ((Width x Aspect Ratio x 2)/2550) + Rim Diameter
Actual Width (in inches) = (width / 25.50)
If you aren't a math guru, here are some common P-Metric Tire sizes converted for you.
1949-1965 Wagon and Utility
These models are hampered by the small rear-wheel openings. The front fenders aren't a problem, and if you stick to skinny tires, larger diameters are possible. Cutting will be required to fit most any modern oversize tire. In the rear, however, there isn't much to cut out before running into the inner fender wells. Add a 4-inch lift and 33s then experiment with backspacing and tread width to clear the rear fenders.
1967-1973 Jeepster Commando and Jeepster
The Jeepsters have small wheel openings, but the outer fender can be cut quite a bit to clear whatever you want. Basically, pick a tire, pick a lift size from the chart, and cut until it's clear. We'd lift it 4 inches or go with a spring over, and then cut until some 35x12.5s fit in there. If it were just a 4-inch lift, we'd expect to be lowering our bumpstops to keep the tires out of the inner fender when really flexing.
1984-2001 XJ Cherokee
These vehicles follow the same guidelines for stock rims as TJs: no more than 10 1/2 inches wide or the tires will always hit suspension components. For our money, we'll go with a set of 35x12.5s on 15x8s, put a 6-inch long arm lift on it, and cut until we're happy.
1993-1998 ZJ Grand Cherokee
Like the rest of the wagons in this line, the small wheel openings with less cuttable area than an XJ are the Grand Cherokee's Achilles' heel. Due to the front control arm design, 10 1/2-inch wide tires won't rub the lower arms on stock rims, but that's about the only advantage. To avoid interference with wider tires, for the most part, go to an aftermarket rim. We'd put 33s on it with 4 to 5 inches of lift and trim as much as possible.
1999-2004 WJ Grand Cherokee
If you've got the checkbook to wheel one of these things, then just find a 4-inch lift for it, put some 33-inch-tall tires on it, and wheel it till it's so beat up you've got to cut the body apart just to open the doors. If you're looking for a more street-friendly ride, just put 1 1/2-inch coil spacers on it with some 31s and run it that way. Either way is wheeling in climate-controlled comfort, so enjoy it. Turn up the stereo if you can hear the tires rubbing.
2005 and up WK Grand Cherokee
Just like the other Grand Cherokees, the same basic tire-size rules apply. You don't have to worry about hitting the lower control arms, but you aren't going to be running a 15-inch rim on these either. Grab a 265/70R17 tire with a 2-inch lift and go run with that. They will rub a bit at full lock, but we'd live with that. With larger tires, other things would start blowing up anyway.
2002-present KJ Liberty
The first year of the Liberty sat about 1 inch higher than the following years. Our chart is really for 2003 and up KJ owners. If you've got an '01, for the most part, you can add an inch to whatever it is we've recommended. Like the Grand Cherokees, this isn't really a hard-core rig - it's more of a dual purpose one. We'd put a 2 1/2-inch lift on it, stuff some 265/75R16s under it, and trim as necessary.
1947-1965 Willys/Kaiser Truck
With the truck bed on the same platform as the wagon of the era, come more cutting options. Stock 31x10.5s will fit, but you'll have to trim some of that fender lip out of the way. The problem with fitting tires on these trucks is the rear fenders. Pull the rear fenders off, and you can put 35s on it. However, on a stock truck, we'd put 33x10.5-inch tires on it with 4 inches of lift with a 1-inch body lift to maintain the truck's appearance.
1957-1965 FC-150 and FC-170
There aren't tons of people running around in these things and unless it was a crew-cab version M-678 or the Swedish Bus, we doubt we'd ever own one. That said, the biggest tires they can clear stock are 30s. You might be able to squeeze a 31-inch tire under it and trim off the 1/2 inch of fender lip as long as the 31 was skinny. Or you could swap FC-170 springs onto the FC-150 for about 2 1/2 inches of lift and the ablility to clear 32s.
1967-1969 Kaiser M-715
The M-715 is based on the Gladiator truck and has the ability to clear 39s at stock height with no fender trimming. The inner fenders in the front are also shared with the Wagoneer and Cherokee. You'll have to get some custom rims to run a normal tire on this one. Get a rim with a 16-inch diameter and 4 inches of backspacing, then put a 39x13.5-inch tire on it and call it done.
1963-1987 Gladiator and J-Truck
As evidenced by the M-715, there is an enormous potential for fitting tires simply by cutting the wheel wells. The inner wheel wells are huge and can clear 35s, but the outer fender isn't made to accept that size tire. Lift it however much you want and then trim the rest away. We'd go with 4 inches of lift and at least 35-inch tires on a rim with less than 4 inches of backspacing. (Possibly up to 38s, depending on how trigger-happy we were on the Sawzall that day.)
1963-1991 Wagoneer and Cherokee
While it does share the front inner wheel wells with the Gladiator, J-Truck, and M-715, the rear is the limiting factor. Whether it's a two-door or a four-door, the inner wheel well in the rear is small, and you'll start running into problems with 35-inch tires. Either cut that inner fender away entirely or stay with 35-inch tires. With a Wide-Trac Cherokee, there might not be any fender-trimming needed, as they come with the larger fender flares to begin with. We'd go with 6 inches of lift and 35x12.5 inch tires on 15x8 inch rims with 3 1/2 inches of backspacing to stay out of the springs. Then we'd go trimming until there was no interference. If we absolutely had to have 38s, we'd either mini-tub the rear or just run no inner fender at all.