Wheel offset — the ET number stamped on a wheel, measured in millimeters — is the distance from the wheel's mounting face to its centerline. Backspacing is the distance from the mounting face to the back edge of the wheel, measured in inches. Both describe the same thing: how far in or out the wheel sits on your truck. To convert between them, use: backspacing = (overall wheel width ÷ 2) + offset.
Positive, Zero, and Negative Offset
Picture a wheel from the side, split down the middle by an imaginary centerline. Offset tells you where the mounting face — the flat surface that bolts against your hub — sits relative to that centerline.
- Positive offset (ET followed by a positive number): the mounting face sits toward the street side of the centerline, so the whole wheel tucks inward toward the truck. Most factory truck and SUV wheels are positive.
- Zero offset (ET0): the mounting face sits exactly on the centerline.
- Negative offset (ET with a minus sign): the mounting face sits toward the brake side, pushing the wheel outward. This is the deep-lip, wide-stance look — what people call "poke."
Lowering the offset number moves the wheel outward and widens your track. Raising it moves the wheel inward. Here is the whole picture in one table:
| Offset | How it's marked | Where the wheel sits | Typically found on | Main rub risk |
|---|---|---|---|---|
| Positive | ET + a number (ET18, ET30…) | Tucked inward, toward the suspension | Factory truck and SUV wheels | Inner: suspension parts, shocks, brake calipers |
| Zero | ET0 | Mounting face on the centerline; wheel splits evenly in and out | Many aftermarket truck wheels | Depends on width — splits the difference |
| Negative | ET − a number (ET-12, ET-25…) | Pushed outward past stock ("poke") | Deep-lip and off-road styles | Outer: fender edges and liners at full steering lock |
Converting Offset to Backspacing (and Back)
Offset is metric and backspacing is imperial, which is why the two numbers confuse people. The relationship is simple:
Backspacing (inches) = (overall wheel width ÷ 2) + offset (converted to inches)
Two details matter. First, convert offset from millimeters to inches by dividing by 25.4. Second, "overall width" is the full outside-to-outside width of the wheel, which runs roughly an inch wider than the advertised width because the advertised figure is measured between the bead seats, not across the flanges. So a wheel sold as 8 inches wide measures about 9 inches overall.
Worked example: a 15x8 wheel with zero offset has an overall width of about 9 inches, so its backspacing is about 4.5 inches. Give that same wheel a negative offset and the backspacing shrinks; go positive and it grows. Spec listings on street and truck wheels — including the Predator and Pegasus lines we stock — usually publish both numbers, so you can cross-check them with this formula.
What Goes Wrong with the Wrong Offset
Too much positive offset — a higher number than stock — pulls the tire deeper into the wheel well. The inner sidewall can contact suspension components, shock bodies, or the inner fender liner, and on some setups the wheel barrel sits too close to the brake caliper to clear it at all.
Too much negative offset pushes the tire past the fender. The outer sidewall can rub the fender edge or liner at full steering lock or when the suspension compresses over a dip. Moving the wheel outboard also changes the scrub radius, which typically means heavier steering feel and more kickback through the wheel, and it adds leverage on wheel bearings and studs. Tires that stick out past the bodywork throw water and gravel down the side of the truck, and many states require fenders or flares to cover the tread — check your state's rules before going wide.
None of this means you must stay at the factory number. Plenty of trucks run a modest offset change without trouble. It means there is no universal "safe" number — clearance depends on your tire size, suspension, and body, so measure before you order.
How to Measure the Wheels You Have
Start with the easy route: check the back of the wheel. Most wheels have the size and offset cast or stamped on the back of a spoke or inside the barrel — something like 15x8 ET-12 — or a backspacing figure on older truck wheels.
No stamp? Measure backspacing directly:
- Take the wheel off the truck and lay it face-down on a flat surface.
- Lay a straightedge across the back lip of the wheel.
- Measure straight down from the straightedge to the mounting face. That distance is your backspacing.
- Measure the overall width, outside edge to outside edge, then run the formula backward: offset = backspacing − (overall width ÷ 2), multiplied by 25.4 to get millimeters.
While the wheel is off, confirm your bolt pattern too — the method in our bolt pattern measuring guide works the same on any wheel, truck or trailer. And when the new wheels go on, tighten them in stages with a torque wrench; our lug nut torque guide covers the crisscross sequence and why a re-check after the first drive matters.
FAQ
What does the ET on a wheel stand for?
It comes from the German word Einpresstiefe, meaning "insertion depth." ET followed by a number is the offset in millimeters: ET30 means 30 mm positive, ET-12 means 12 mm negative, and ET0 means the mounting face sits right on the centerline.
Will a lower offset make my wheels stick out more?
Yes. Every millimeter lower (or more negative) moves the wheel that much farther outboard. Width matters too: a wider wheel at the same offset gains lip on the outside and barrel on the inside at the same time, so check clearance in both directions.
Can I run a different offset than my truck came with?
Often, yes — modest changes are common on pickups. But there is no one-size answer: clearance depends on tire size, suspension travel, and steering lock. Compare the new wheel's backspacing against your measured stock figure, and test-fit before mounting tires if the numbers are close.
Every wheel at Cheap2Go Tires lists its offset and backspacing in the specs — browse the wheel collection and your order ships free from our Orlando warehouse; for a second opinion on fitment, call (407) 821-7008.