Wheel Offset Vs. Wheel Backspacing

Are you looking to buy new wheels for your truck, Jeep®, or SUV? Aside from the standard measurements of diameter, width, and bolt circle, there are a few other values you should be familiar with. Of course, I'm referring to a wheel’s offset and backspacing—two values directly correlating to fitment.​

You’ve likely heard these two terms before, or at least, have read them on the spec sheets of industry-leading wheel manufacturers and retailers, like RealTruck. However, without the proper knowledge, these values are nothing more than a jumbled mess of numbers.​

At RealTruck, we’re more than just a retailer—we’re a provider of world-class, in-house-manufactured parts and concise, accurate information about all things truck, Jeep®, and off-road. In this article, we’re adding to our ever-expanding article library with a comprehensive overview of the ins and outs of backspacing and offset, including what these two values measure, the units of measurement used, how each is calculated, and how they differ. And by the end of this article, you’ll be a wheel fitment expert.

Wheel offset refers to the distance of a wheel’s mounting flange, or the flat portion of the wheel that fits against your vehicle’s hub, from the wheel’s centerline, measured in millimeters. For example, if a wheel is eight inches wide and carries a +0 mm offset, the mounting flange is positioned at the exact centerline of the wheel, with four inches to the front and four inches to the rear.

If you’re unsure of a wheel’s offset, manufacturers will typically etch the specs into the rear of the wheel’s face or barrel. If not, you’ll have to calculate the offset manually—fortunately, this can be done easily with a straight edge, a dismounted wheel, and a measuring tape.​

• Step 1: Measure the wheel's total width. To do so, lay the wheel face down on a flat, non-abrasive surface, such as a piece of plywood or a rubber mat. Place a straightedge across the rear lip of the wheel. Then, measure the entire width of the wheel—from the ground (face) to the straight edge (rear lip). Convert this measurement to millimeters. For the sake of this example, we’ll assume that we’re using a 10-in.-wide wheel (254 mm).

• Step 2: We’ll then need to find the wheel's centerline. Using the previous measurement, divide the value (in millimeters) by two. In this example, the centerline will be 254 mm divided by two, or 127 mm.

• Step 3: Next, we need to measure the distance from the wheel’s mounting flange (the part that rests against the rotor/hub) to the wheel's rear lip. For this example, let’s assume that this measurement is 112 mm.

• Step 4: Using these two measurements, we can calculate the wheel’s offset. Subtract the wheel’s centerline measurement (127 mm) from the hub-to-wheel distance (112 mm). In this example, 112 - 127 = -15, which is the wheel’s offset in millimeters.

As previously mentioned, a wheel's offset can either be positive, negative, or neutral, depending on which direction the mounting flange deviates from the wheel’s centerline. 

• Positive Offset: A wheel in which the mounting flange is pushed closer to the outer lip, resulting in a recessed, sunken-in appearance. 

• Negative Offset: A wheel with the mounting flange positioned further inward from the wheel’s centerline, thus prompting the wheel to protrude further from the body.

• Zero Offset: A neutral offset wheel, or “zero offset”, features a mounting flange that’s positioned directly in the centerline of the wheel’s barrel. 

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Most factory wheels feature a high offset, such as a +45, which keeps the wheel tucked tightly against the body and prevents water, mud, and kicked-up debris from splashing onto other drivers. 

However, many aftermarket wheels feature zero or lower offsets, which push the wheel further outward for a “flush” appearance—where the wheel is practically aligned with the upper edge of the fender. Excessive “poke,” in which the wheel protrudes past the fender, is also a popular look. However, modifications such as fender flares may be required to ensure adequate tire coverage.  

While one may assume a wheel’s offset only impacts aesthetics, that’s not the case. Incorrect offset can also negatively impact performance. The lower the offset, the further the wheels protrude from the body—which can impact factors like:​

• Scrub Radius: The distance at the road surface between your tire's vertical centerline and the projected steering axis.

• Steering Feel: The higher the scrub radius, the heavier the steering and more likely it is to follow bumps and dips in the road.

• Suspension Load: The lower the offset, the more leverage and stress is placed on suspension and steering components, which can accelerate wear.

After installing a lift kit, you’ll likely want to install wider, oversized tires and lower-offset wheels to fill out the fender wells. When spec-ing out your setup, it’s important to select a wheel and tire combo that fits your application—as in, the outside of the tire doesn’t rub the fenders while turning, nor does the inside contact any suspension components. Fortunately, most lift installation instructions, as well as our RealSource™ tire size guides, include several recommendations for tire and wheel specs depending on lift height.

Common Offsets by Lift Height

While every truck is different, the general rule of thumb is that the taller the lift, the further negative your wheel’s offset can be without clearance issues. Now, that’s not without nuance—too wide of wheels or too large of tires can always cause clearance issues, regardless of offset. However, if we’re comparing the same width wheel and tire size (for instance, a 9-in. wide wheel mounted to a 35x12.50 tire) each incremental jump in lift height increases tire clearance, allowing for a lower offset.

What if you’ve already purchased aftermarket wheels, but the offset is too high for adequate clearance after installing a lift kit? That’s where wheel spacers can come in handy. These accessories mount between your vehicle’s hub and the wheel, effectively “spacing” the wheel outward from the hub by the width of the spacer.​

Available in bolt-on (adapter-style) and slip-on configurations, wheel spacers can be a solid solution for incorrect offset—so long as you select the right-size spacers and install them according to the manufacturer’s instructions.

Before committing to spacers as a fitment fix, it's worth understanding the full picture. Not all spacers are created equal, and the wrong type or size can introduce new problems. Read our in-depth guide on whether wheel spacers are safe for your truck before making a call.

With a basic understanding of offset under our belts, let’s get into our next value—backspacing. Backspacing is a similar measurement, though it is not calculated in the same way or with the same units. This numerical value describes the distance from the mounting flange to the wheel's rear lip, in inches.

Returning to the example above, in which a wheel is 10 inches wide with a -15 mm offset, the backspacing is simply the measurement, in inches, from the wheel’s mounting flange to the rear lip.​

If you remember, we calculated this measurement in Step 3 of our previous example. At 112 mm, the aforementioned wheel has a backspacing of approximately 4.041 inches.​

Before ordering a set of wheels for your ride, measure for clearance between the vehicle’s hub and any suspension components, brake lines, etc. Don’t choose a wheel with a backspacing close to or greater than this distance, as doing so may result in rubbing and clearance issues. For additional tips on recommended, rub-free tire sizing, check out our assorted tire size guides:​

• Jeep Wrangler Tire Size Guide

• Toyota Tacoma Tire Size Guide

• Ford F-150 Tire Size Guide

• GMC Sierra 1500 Tire Size Guide

Backspacing alone doesn’t necessarily inform fitment—instead, the relation of a wheel’s width and its backspacing does.​

Typically, the less backspacing, the further a wheel sticks outwards. For example, an 8-in.-wide wheel with a 4-in. backspacing will sit further recessed than an 8-in-wide wheel with a 3-in. backspacing. Alternatively, a 10-in.-wide wheel with a 4-in. backspacing will stick out significantly farther than an 8-in.-wide wheel with a 4-in. backspacing, since the distance from the mounting flange to the outer lip has increased by two inches.

Backspacing matters on every application, but especially on lifted trucks. Larger tires—both wider and taller—reduce the clearance between tires and suspension components. Additionally, many lift kits—especially on IFS (independent front suspension) applications—feature aftermarket steering knuckles and control arms that, while providing greater support and correcting steering geometry, further minimize clearances. In fact, some lift kits even specify aftermarket, lower-offset wheels (or spacers) as a requirement.

Before spending loads on new shoes for your truck, contact the lift manufacturer and thoroughly read the lift instructions for wheel and tire guidelines.

What size wheels should you install with your lift kit? In most cases, wheel diameter has little to no bearing on offset, meaning you’ll be able to find wheels of any size with a compatible offset. 

The only instances where wheel diameter affects fitment are brake and suspension clearance. So long as the wheel’s inner barrel clears the brakes and steering knuckles, diameter is flexible. 

Where wheel diameter comes into play is wheel–sidewall ratio, which significantly affects performance on and off-road. Check out the chart below for some recommended wheel diameters, pros, cons, and recommended usage.

So, what are the key differences between these values? For starters, both are measured in different units—backspacing in inches and offset in millimeters. Additionally, offset uses negative and positive values, whereas backspacing uses only positive values.​

With these surface-level differences aside, we can view the two measurements in relation to one another rather than focus on their differences. With other values defined, like a wheel’s width, these two measurements essentially determine the same thing—the position of the wheel’s mounting flange—only offset measures this value in relation to the wheel’s centerline, and backspacing measures this value in relation to the wheel’s rear lip.​

You can also use these values to determine one another. For instance, if we know that a 9-in-wide wheel has a +25 mm offset (one inch), then we know that the mounting flange is pushed one inch towards the wheel's outer face. To determine the backspacing, simply divide the wheel’s width by two (in inches) and add or subtract the offset. In this case, we’d perform 9/2 + 1, giving us a backspacing of 5.5 inches.​

Alternatively, if we know the backspacing and width of the same wheel, we can use a similar equation to determine the offset. In this example, divide the width by two, and subtract the resulting value from the backspacing. In this case, we’d perform 5.5 - (9/2), yielding an offset of one inch, or +25 mm.​

So what have we learned? Let’s look at a few key takeaways:​

• Backspacing is the distance of a wheel’s mounting flange to the rear lip in inches.

• Offset is the distance from the centerline of a wheel's mounting flange, measured in millimeters.

• Both values accomplish essentially the same measurement in different ways (the position of a wheel’s mounting flange).

• Both values are related, but not identical.

• Offsets can be positive or negative.

• Backspacing only presents as positive values.

• Both values help determine the position of a wheel relative to your vehicle’s body.

What Offset Do I Need for My Truck?

It depends on the look you're after and your truck's clearance requirements. Most factory truck wheels have a positive offset of +10 to +44 mm, which keeps the wheel tucked close to the body. Aftermarket wheels typically feature negative or low offsets to push the wheel outward for a more aggressive stance. Before choosing an offset, measure the clearance between your hub and any suspension components, brake lines and inner fender to avoid rubbing.

Can the Wrong Offset Damage My Truck?

Yes. Running an offset that's too low — pushing the wheel too far outward — can cause the tire to contact the fender or fender liner, especially under load or during turns. Too high an offset pushes the wheel too far inward, where it can contact suspension components, brake calipers or brake lines. Either scenario can cause premature wear or component damage.

Is Backspacing or Offset More Important for Fitment?

Neither is more important than the other — they're two ways of describing the same thing. Most modern wheel manufacturers specify offset in millimeters, while backspacing is still commonly used by domestic wheel brands and older references. Knowing how to work with both and convert between them gives you the full picture when comparing wheels across different brands.

Can I Use a Wheel Spacer to Fix My Offset?

Yes. Wheel spacers can effectively push a wheel outward, increasing its negative offset. While ordering wheels with the correct specifications is the best solution, spacers can be a functional alternative.