Wheel Offset and Backspacing Explained (and How to Measure Yours)

Offset and backspacing are the same wheel measured from two different points, and getting either wrong means bearings, fenders, or steering geometry pay the price sooner or later.

David K.·Guides·8 min read·Published 16 September 2026

Wheel offset explained plainly: it’s the distance, in millimeters, from a wheel’s true centerline to the face that bolts against the hub, and that single number decides whether a wheel tucks in under the fender or hangs out past it. Positive offset pulls the wheel and tire in toward the truck’s centerline. Negative offset pushes them out. This page settles the whole measurement cluster in one place — offset, its cousin backspacing, how to measure both on a wheel sitting in your garage, and what running more negative offset does to steering feel and wheel-bearing life.

Offset and backspacing describe the same wheel from two different reference points, and confusing them is the single most common reason people order the wrong wheel. Neither number has anything to do with tire diameter or section width — that’s a separate question, covered on What Size Tires Fit My Jeep? — offset only tells you where the wheel sits relative to the hub once a tire is mounted on it. For everything else wheel- and tire-related, the wheels and tires hub is the place to start.

Wheel Offset Explained: Positive, Zero, and Negative

Every wheel has a true centerline — the midpoint between its two bead lips — and a mounting face, the flat pad where the lug holes pass through and the wheel bolts to the hub. Offset is the gap between those two planes, stamped on the back of most wheels as “ET” followed by a number in millimeters (ET35, ET-12, and so on).

• Positive offset — the mounting face sits outboard of centerline, toward the street side. The wheel and tire pull in under the truck. Most factory wheels on unlifted trucks run moderate positive offset, typically somewhere in the +20mm to +40mm range depending on platform and trim, though the exact figure varies enough by wheel and model year that it’s worth checking your specific wheel rather than assuming.
• Zero offset — the mounting face sits exactly at centerline. The wheel sits neither in nor out relative to where a true center-mount wheel would land.
• Negative offset — the mounting face sits inboard of centerline, toward the truck. The wheel and tire push out, widening the stance. This is the range most aftermarket off-road wheels live in, because a wider stance improves stability and gives a taller tire more room to clear the fender well at full steering lock.

Offset and Backspacing Are Not the Same Number

Backspacing measures from the wheel’s mounting face to the back inside lip — always a positive number, always in inches, and it never tells you where centerline actually is unless you also know the wheel’s true width. Two wheels can share identical backspacing and still have different offset if they’re different widths, which is exactly how people end up ordering a wheel that measures “right” on paper and still rubs.

The conversion runs through the wheel’s true width, measured bead-lip to bead-lip rather than the nominal size stamped on the wheel — actual measured width typically runs about three-quarters of an inch to an inch wider than the marketed number:

Backspacing (inches) = (width ÷ 2) + (offset in mm ÷ 25.4)

Run that formula backward and you get offset from backspacing. Here’s the conversion for three common wheel widths across a spread of offsets, using nominal width for reference:

Notice the pattern: for a fixed width, backspacing climbs as offset moves toward positive. A 9-inch wheel at zero offset backspaces to 4.5 inches; push that same wheel to +25mm and backspacing climbs past 5.4 inches, because more of the wheel’s depth now sits inboard of the mounting face.

How to Measure a Wheel with a Straightedge and a Ruler

You don’t need a shop to get real numbers off a wheel you already own — a straightedge, a tape measure, and about ten minutes on the garage floor will do it.

1. Measure the wheel’s true width, bead-lip to bead-lip, with the tape measure laid flat across the front face. Divide by two — that’s your centerline reference.
2. Lay the straightedge across the face of the wheel so it rests on both bead lips.
3. Measure straight down from the underside of the straightedge to the wheel’s mounting pad — the flat ring the lug holes pass through. That distance is your backspacing, in inches.
4. Subtract half the true width (step 1) from the backspacing (step 3), then multiply the result by 25.4. A positive result is positive offset, in millimeters; a negative result is negative offset.

Do this on the wheel you’re planning to replace before you order anything new. Manufacturer spec sheets are usually accurate, but a wheel that’s been re-drilled, straightened after a curb hit, or sold under a generic listing sometimes isn’t exactly what the box claims.

What Negative Offset Does to Scrub Radius, Bearing Load, and Fender Clearance

Pushing the wheel and tire outward doesn’t just change how a truck looks. It changes the geometry the steering and suspension were designed around, and the further you go from the factory number, the more that geometry pushes back.

Scrub radius is the distance between the steering axis — the line through the ball joints, extended down to the ground — and the center of the tire’s contact patch. Negative offset moves the contact patch outward, away from that axis, which increases scrub radius. The practical result is heavier steering effort at low speed, more kickback transmitted through the wheel over rough ground, and a stronger pull to one side under hard braking if a caliper is even slightly sticky or the road surface isn’t level from side to side.

Bearing load works on simple leverage. The wheel bearing sits at the hub; the tire’s contact patch sits out at the end of the offset. The more negative the offset, the longer that lever arm, and the more bending load the bearing, ball joints, and tie-rod ends carry with every pothole and every turn. Factory bearings are sized around the factory offset range. Stack a heavy negative offset with a heavier tire — a 35-inch mud-terrain instead of a stock all-terrain — and a bearing rated for one load ends up carrying meaningfully more, for the life of the truck.

Fender clearance is the one people actually notice. Negative offset pushes the tire’s outer edge toward the fender lip, and the geometry that matters isn’t static ride height — it’s full suspension compression and full steering lock happening together, which is when a tire sits closest to the fender liner and the inner edge of the wheel well. A combination that clears easily in the driveway can still tag the fender on a washboard road with the wheel cranked over. This is why aftermarket wheels with meaningful negative offset are almost always paired with a lift kit — the added height buys back clearance the offset just spent.

Retorque the lug nuts within the first 50 to 100 miles on any new wheel, negative offset or not. New wheels seat against the hub as they’re driven, and factory torque specs assume a properly seated wheel.

Which Offset to Run

There’s no single correct number — it depends on tire size, whether the truck is lifted, and what it actually does. A few starting points:

• If you’re running stock-sized tires and just want a slightly wider stance, stay within roughly 12mm of the factory offset. Beyond that you start trading noticeably into steering effort and bearing load for a look a wheel spacer or a modestly wider wheel could deliver with less change to the geometry.
• If you’re building for rock crawling and plan to run 35s or 37s, favor an offset closer to zero than deeply negative. The heavier tire already adds leverage on the bearings; stacking that with aggressive negative offset compounds it faster than most people expect.
• If the truck already has wheel spacers installed, don’t also buy a deeply negative-offset wheel — the two stack, and the combined leverage on ball joints and tie-rod ends can exceed what either was designed to carry alone. See Are Wheel Spacers Safe? for where that line actually sits.
• If the build runs beadlock wheels for low-pressure crawling, offset still matters exactly as much as it does on a standard wheel — a beadlock ring adds weight out at the rim, which increases the bending load a negative offset multiplies. Read What Are Beadlock Wheels? before assuming the ring changes anything about how offset behaves.

Common questions

What’s a good wheel offset for a Jeep Wrangler running 35-inch tires?

Most Wrangler builds running 35s land somewhere between 0mm and -12mm on a 17-inch wheel, paired with a 2 to 3.5-inch lift for clearance at full articulation. Going more negative than that without a lift usually means fender trimming or persistent rubbing at full steering lock.

Does running negative offset always require a lift?

Not always, but usually past about -12mm on a stock-height truck, because the tire moves outward faster than the fender well can absorb it at full compression. Mild negative offset on stock-sized tires can sometimes clear without any lift — check at full steering lock before assuming it will.

Can the front and rear wheels run different offset?

Yes, and on some solid-axle trucks it’s normal — rear fenders often have more room than front fenders, which have to clear the wheel through a full steering sweep. Check clearance at both ends independently rather than assuming one offset number works everywhere on the truck.

What does the “ET” number stamped on a wheel mean?

ET stands for Einpresstiefe, a German term meaning insertion depth, and the number that follows it is offset in millimeters. ET35 is +35mm offset; ET-12 is -12mm. It’s the same number this whole page has been discussing, just under its factory label.

Is more backspacing the same thing as more positive offset?

Only if the wheel width stays the same. Backspacing and offset move together on a single wheel, but comparing backspacing across two different widths without converting to offset first will get you the wrong wheel — that’s the whole reason the conversion table above exists.