Jeep Tire Size Calculator and Comparison: Diameter, Width, Sidewall, and What Changes When You Go Bigger

A Jeep tire size is three numbers, and once you know what each one means, you can work out the overall diameter, the sidewall height, the circumference, and how many times the tire turns in a mile with nothing but a calculator. Overall diameter is what matters most: it sets ground clearance under the axles, it changes your effective gear ratio, and it throws off the speedometer and odometer by the same percentage it grows. The tool below does the math for any two sizes, metric or flotation, and shows what changes when you go bigger. Below the tool, you will find the formulas it uses, a comparison of the sizes Jeep owners actually run, and the real reason a "35" from one brand measures 34.4 inches and from another measures 35.1.

In this article

• Jeep tire size calculator
• The formulas, worked once
• What the numbers on the sidewall mean
• Common Jeep tire sizes compared
• Why a 35 is rarely 35 inches
• How diameter changes your gearing
• Speedometer and odometer error
• When a bigger tire needs a lift or trimming
• The spare has to follow
• Frequently asked questions

Jeep tire size calculator

Type your current size and the size you are considering. Metric sizes look like 285/70R17; flotation sizes look like 35x12.50R17. A leading LT or P, and a trailing letter like C or LT, are ignored, so you can copy the size straight off the sidewall. The results use the nominal (calculated) dimensions, so for the exact number on a specific tire, check that tire's spec page, as explained further down.

The formulas, worked once

The calculator uses the same arithmetic Tire Rack lays out in its tire dimensions guide. A metric size gives you the section width in millimeters, the sidewall height as a percentage of that width, and the wheel diameter in inches, so the overall diameter is the wheel plus two sidewalls:

• Sidewall height (mm) = section width x aspect ratio / 100
• Overall diameter (in) = rim diameter + 2 x sidewall height / 25.4
• Circumference (in) = pi x overall diameter
• Revolutions per mile = 63,360 / (pi x overall diameter in inches), because a mile is 63,360 inches

Take the Rubicon's stock 285/70R17. The sidewall is 285 x 0.70 = 199.5 mm, which is 7.85 inches. Two sidewalls plus a 17-inch wheel is 17 + 2 x 7.85 = 32.71 inches overall. Circumference is 3.1416 x 32.71 = 102.76 inches, and 63,360 divided by 102.76 gives 617 revolutions per mile. Section width is 285 / 25.4 = 11.22 inches.

A flotation size skips the arithmetic. In 35x12.50R17, the first number is the overall diameter in inches, the second is the section width in inches, and the last is the wheel diameter. Sidewall height is (35 - 17) / 2 = 9 inches, circumference is 109.96 inches, and revolutions per mile is 576.

What the numbers on the sidewall mean

Everything on the sidewall follows a convention, and Tire Rack's sidewall guide spells it out. On a metric size such as LT285/70R17 116/113S:

• LT in front means a light truck metric size built for heavier loads. P in front means a P-metric passenger size. No letter at all means a Euro-metric size.
• 285 is the section width in millimeters, sidewall to sidewall.
• 70 is the aspect ratio: the sidewall height is 70 percent of the section width.
• R is radial construction. A D here would mean bias-ply.
• 17 is the wheel diameter in inches.
• 116/113S is the service description: load index for single and dual fitment, then the speed rating.

Flotation sizes put the inch measurements up front, which is why off-road tires are marketed by them. In 35x12.50R17LT, the 35 is the nominal overall diameter in inches, 12.50 is the nominal section width in inches, R17 is the wheel, and the trailing LT marks it as a light truck flotation size. The same guide notes that a trailing LT means flotation sizing, while a leading LT means light truck metric; both are built for cargo and towing loads, they just describe the tire differently.

One more wrinkle: section width depends on the wheel it is mounted on. Every size is measured on a specific rim width, and Tire Rack's rule of thumb is that section width changes by 0.2 inch for every 0.5 inch of rim width above or below the measuring rim. The calculator reports the nominal width, so when you are an inch from a control arm, measure.

Common Jeep tire sizes compared

These are the sizes most Wrangler conversations come down to. The first two are factory sizes: the 2024 Wrangler specifications from Stellantis list P245/75R17 as standard on Sport, P255/70R18 on Sahara, LT285/70R17C on Rubicon and Willys, and LT315/70R17C on the Xtreme 35 package and Rubicon 392. The rest are the aftermarket steps everyone considers. All figures below are nominal, computed with the formulas above.

Two things jump out. First, the Rubicon's "33-inch" tire is a 32.7 on paper, and Jeep's own "35-inch" tire, the LT315/70R17, is a 34.4 on paper. Second, revolutions per mile fall as diameter grows, and that single number is what the speedometer, the odometer, and the transmission all respond to. Compare the computed 617 revs per mile for 285/70R17 with the 637 Stellantis publishes for the KO2 it fits to the Rubicon, and the 587 computed for LT315/70R17 with the 604 Stellantis publishes for the Xtreme 35 tire. Spec-sheet revs per mile are measured on a loaded, rolling tire, which flattens at the contact patch, so they run a few percent above the geometric figure: about 3 percent for the two Jeep-fitted KO2 sizes in the table, closer to 5 percent for some other tires. For a comparison between two tires, that difference washes out, because both tires are off by about the same share.

Why a 35 is rarely 35 inches

The number in a flotation size is a nominal figure, and Tire Rack says it plainly in its dimensions guide: calculated dimensions "only reflect nominal tire dimensions," which can differ subtly or substantially from the tire's actual size, and anyone working with tight fitment tolerances should use the manufacturer's specifications for the exact tire. The tire's tread depth, carcass, and mold all move the real diameter around, and the Tire Rack light truck size chart puts 35x12.50R17LT in its 34-1/2 inch row for that reason. Here is what three real tires in the same marketed size measure, straight from their spec pages:

Same marketed size, seven tenths of an inch of spread. The same pages put the 33x12.50R17 at 32.5 (KO2) and 32.8 (Ridge Grappler), and the 37x12.50R17 at 36.5, 36.8, and a full 37.0 (Wildpeak A/T4W). The practical rule is simple. Use the calculator to compare sizes and understand the percentage change; then, before you buy, open the spec page for the exact tire and read the overall diameter it was measured at. If fender clearance is going to be close, that tenth of an inch is the one that matters.

How diameter changes your gearing

A taller tire covers more ground per turn, so the engine turns fewer times per mile and the Jeep behaves as if it had numerically lower axle gears. Tire Rack's light truck fitment formulas give the relationship directly: effective axle ratio = (original diameter / new diameter) x original ratio. Going from the Sport's 31.47-inch tire to a 35 on the Sport's 3.45 axle leaves you with an effective 3.10. That is why acceleration goes soft and the transmission hunts on grades, and it is also why Jeep ships its own 35-inch package with 4.56 gears instead of the Rubicon's standard ratio. The percentage you see in the calculator's diameter change line is the percentage your gearing lost. To find the ratio that puts it back, use the Jeep gear ratio calculator, which takes your current ratio and both tire sizes and returns the nearest common ring and pinion.

Speedometer and odometer error

The speedometer does not measure speed. It counts wheel rotations and multiplies by the circumference the factory programmed in. Put on a tire that is 11 percent bigger around and every rotation covers 11 percent more road than the computer thinks, so the dash reads 11 percent low. Tire Rack's formula is the same one the calculator uses: actual speed = (new diameter / original diameter) x indicated speed. A Sport that moves from 245/75R17 to 35x12.50R17 is doing 72.3 mph when the needle says 65.

The odometer uses the same count, so it logs fewer miles than you drive by the same percentage. On that Sport, 1,000 miles on the dash is 1,112 miles on the road, which quietly shortens every service interval and understates fuel economy. Both errors are fixed by reprogramming the tire size with a dealer tool or an aftermarket programmer, and the fix is worth doing even on a modest change: a 285/70R17 to 33x12.50R17 swap is under 1 percent, but a Sport going to 33s is nearly 5 percent, which is 3 mph at highway speed.

When a bigger tire needs a lift or trimming

Diameter raises the Jeep; width is what rubs. Tire Rack's fitment guide gives the first half of that: the change in ground clearance under the axles, and in the vehicle's center of gravity, is (new diameter minus original diameter) divided by 2, because only the half of the tire below the axle is lifting anything. A 245/75R17 to 35x12.50R17 change is 3.53 inches in diameter, so the axles and body rise about 1.77 inches. The sidewall above the axle is the half that has to clear the fender and the inner liner, and it needs that room at full suspension compression and full steering lock, not just sitting in the driveway.

The clearest manufacturer guidance is what Jeep itself does. Per the Xtreme Recon package announcement, Jeep's factory 35-inch fitment on the Wrangler Rubicon consists of LT315/70R17C BFGoodrich KO2 tires on 17x8 beadlock-capable wheels, a 4.56:1 axle ratio, and a 1.5-inch factory suspension lift with its own shock tuning, and the 2024 spec sheet puts that combination at 12.9 inches of ground clearance against 10.8 for a standard Rubicon and 9.7 for a Sport. In other words, Jeep's engineers chose a 34.4-inch tire, a modest lift, and a regear to deliver a "35." Above that size, nothing comes from the factory, so there is no manufacturer number to lean on; a lift, a fitment check through full articulation, and a regear are the standard package, and clearance has to be confirmed with your specific wheels, since wheel width and offset move the tire relative to the control arms as much as the tire size does. Wheel fitment basics are in the bolt pattern and torque spec guide.

Also check load range and speed rating when you step up. The flotation 35s above are load range E with load index 121 or higher, and a Sport's stock P245/75R17 is not. The all-terrain tires for highway driving guide covers how the heavier LT carcass changes the ride.

The spare has to follow

Whatever size goes on the four corners should go on the tailgate too. A spare that is 3 inches shorter than the other three tires on an axle is a different rolling circumference, which matters for a limited-slip or locker and for the traction control's wheel-speed math, and it makes five-tire rotation impossible. The bigger spare also changes what fits around it, from the tailgate carrier to the cover. The stock vs. lifted tire cover sizing guide explains how to measure the spare you actually have, since, as the spec pages above show, a "35" can be anywhere from 34.4 to 35.1 inches depending on which tire it is.

Frequently asked questions

How do I calculate tire diameter from a metric size like 285/70R17?

Multiply the width by the aspect ratio to get the sidewall in millimeters (285 x 0.70 = 199.5 mm), convert to inches (7.85 in), double it, and add the wheel diameter: 17 + 2 x 7.85 = 32.71 inches. That is the nominal figure; the manufacturer's spec page gives the measured one for a specific tire.

Is a 285/70R17 the same as a 33-inch tire?

Close enough that Jeep calls the Rubicon's LT285/70R17 a 33-inch tire, but on paper it is 32.71 inches, and BFGoodrich's KO2 in that size is published at 32.8 inches. A true 33x12.50R17 is nominally 33.0 inches and 12.5 inches wide, so it is a little taller and more than an inch wider.

What size is a 35-inch tire in metric?

The nearest common metric sizes are LT315/70R17 (34.36 inches nominal, Jeep's factory 35-inch tire) and LT295/70R18 or LT285/75R18, which land in the 34 to 35 inch range. No metric size works out to exactly 35.00 inches, which is one reason the off-road market uses flotation sizes.

How far off is my speedometer with 35s on a stock Sport?

Going from 245/75R17 (31.47 in) to a nominal 35 is an 11.2 percent increase in diameter, so the speedometer reads 11.2 percent low: 65 indicated is 72.3 actual. The odometer logs 1,000 miles for every 1,112 driven. Reprogramming the tire size fixes both.

Do 35s need a lift on a Wrangler JL?

Jeep's own answer is yes, a small one: the factory Xtreme 35 package fits LT315/70R17 tires with a 1.5-inch suspension lift, 17x8 wheels, and 4.56 gears. Anything taller than that has no factory precedent, so you must verify clearance at full compression and full steering lock on your Jeep with your wheels.

Why does the spec sheet show more revolutions per mile than the formula gives?

The formula uses the unloaded diameter. A spec sheet figure is measured with the tire loaded and rolling, and a loaded tire flattens at the contact patch, so its rolling radius is smaller and it turns more times per mile, typically a few percent more. When comparing two tires, the difference cancels out, because both are affected by about the same amount.

Related reading on this site: Jeep gear ratio calculator, tire cover sizing for stock vs. lifted Jeeps, best all-terrain tires for highway driving, Jeep wheel bolt pattern and torque specs by generation.