Free Wheel Offset Calculator & Fitment Comparison Tool
Compare your current wheel to a new one and instantly see offset, backspacing, frontspacing, outer poke, and how much closer or further the inner lip sits from the suspension. The fitment diagram updates as you type.
Calculate Wheel Offset, Backspacing & Frontspacing
Enter width, offset, and spacer — backspacing, frontspacing, and the diagram update as you type
Inner lip, toward the suspension
Outer lip, toward the street
Inner lip, toward the suspension
Outer lip, toward the street
Understanding Wheel Offset, Backspacing & Spacers
Wheel offset—often stamped as “ET” (from the German Einpresstiefe)—is the distance in millimeters from the wheel’s hub mounting surface to the true centerline of the rim. Backspacing and frontspacing describe the same mounting-face location from the inner and outer lips. Together they tell you how far the wheel tucks toward the suspension and how far it pokes toward the street. Spacers reduce effective offset and push the whole wheel outward.
Positive Offset (Higher ET)
With a positive offset the hub mounting surface sits toward the street-facing side of the wheel. This tucks the wheel and tire deeper into the fender well, closer to the strut or coil-over. Most factory vehicles—especially passenger cars and crossovers—run positive offsets between ET30 and ET50. Higher positive offset keeps the scrub radius small for stable, predictable steering.
Negative Offset (Lower ET)
A negative offset pushes the hub mounting surface behind the centerline, moving the wheel outward past the fender lip. This creates an aggressive, “deep-dish” look popular on lifted trucks, Jeeps, and off-road builds. Be aware that aggressive negative offsets increase the scrub radius, add leverage on wheel bearings, and can cause tires to rub on fenders during turns or suspension travel.
Zero Offset & Centerline
Zero offset means the mounting surface is exactly at the wheel’s centerline. It serves as the neutral reference point: any value above zero is positive offset, and any value below is negative. Many classic truck wheels and aftermarket deep-lip wheels sit at or near zero offset.
What Is Backspacing?
Backspacing is the distance from the wheel’s inner lip (the side facing the suspension, brakes, and inner fender) to the hub mounting surface, usually listed in inches. More backspacing tucks the barrel further in toward the strut. Less backspacing pulls the inner lip away from the suspension and gives you more inner clearance. If you’ve ever installed wheels that rubbed a control arm, shock, or caliper, backspacing was the number that was off.
What Is Frontspacing?
Frontspacing is the matching measurement on the street side: from the mounting face to the outer lip. It controls poke, fender clearance, and how flush the setup looks. Wider wheels with the same offset add both backspacing and frontspacing—the extra width grows inward and outward from the hub. That is why a 1" wider wheel at the same ET sits closer to the suspension and further past the fender.
Offset vs. Backspacing
Offset is measured in millimeters from the centerline. Backspacing is measured in inches from the inner lip. They describe the same mounting-face position two ways, which is why spec sheets mix them. Formula (including typical 0.5" lips on each side): Backspacing (in) = (Width + 1) ÷ 2 + Offset ÷ 25.4. Frontspacing is (Width + 1) ÷ 2 − Offset ÷ 25.4. Enter width, offset, and spacer above—both spacing numbers fill in automatically.
Inner Clearance (Suspension Side)
The calculator reports how much closer or further the inner lip sits compared with your current wheel—not just outer poke. More backspacing (or a wider wheel at the same offset) moves metal toward the strut, coil-over, UCA, and brake caliper. Less backspacing or a spacer moves it away. Always check inner clearance at full lock and full droop, not just how the wheel looks from the fender.
How Wheel Spacers Work
A spacer bolts between the hub and the wheel, physically pushing the wheel outward. A 25 mm spacer on a wheel stamped ET45 gives you an effective offset of ET20 and reduces effective backspacing by the same 25 mm (about 1"). That buys inner clearance and adds poke. Always use hub-centric spacers with the correct bolt pattern and torque specs, then re-torque after the first 50 miles.
Fitment & Safety Considerations
Changing offset or backspacing by more than 10–15 mm in either direction can affect fender clearance, inner suspension clearance, turning radius, ABS sensor alignment, and tire wear. Always test-fit at full steering lock and full suspension droop before committing. For lifted trucks or aggressive builds, consult a professional—Platinum Wheels offers free fitment consultations at our Denver shop.
How to Use the Wheel Offset Calculator
- Start with the diagram – a sample current vs. new setup is already drawn so you can see how the tool works before you type anything.
- Enter your current wheel – width (inches), offset / ET (mm), and spacer if you run one. Backspacing and frontspacing fill in automatically.
- Enter the new wheel the same way.
- Read both sides of the diagram – inner lip (suspension) on the left, outer lip (street) on the right.
- Share the URL – tap “Update Comparison & Share Link” to copy a link with your specs for a friend, installer, or forum post.
Frequently Asked Questions About Wheel Offset & Backspacing
What offset do I need for a flush fitment?
A “flush” look typically requires the outer lip of the tire to sit nearly even with the fender. The exact offset depends on your vehicle’s hub width, fender arch, and tire size. Use our calculator to compare a few options, then bring the results to our Denver shop for a professional recommendation.
Why does a wider wheel rub the suspension if offset stays the same?
Width grows both directions from the centerline. At the same ET, a 1" wider wheel adds about 12.7 mm of backspacing and 12.7 mm of frontspacing. The inner lip moves closer to the strut even though the stamped offset never changed. Check the inner-clearance number, not just poke.
Is more backspacing better?
Only if you need the wheel tucked in. Extra backspacing is what hits UCAs, shocks, and calipers. Less backspacing (or a spacer) is what hits fenders and outer liners. The right number is the one that clears both sides on your vehicle, not a bigger or smaller figure in the abstract.
Will changing my wheel offset void my warranty?
Manufacturer warranties vary. Minor offset changes (5–10 mm) are generally considered safe and rarely affect warranty coverage. Extreme changes that cause accelerated wear or component damage could be a different story—always check with your dealer.
Can I run spacers instead of buying new wheels?
Yes. Quality hub-centric spacers are a safe and affordable way to effectively lower your offset and reduce backspacing. Make sure they match your bolt pattern and hub bore, and re-torque after the first 50 miles.
What is wheel poke?
“Poke” is how far the outer lip extends toward (or past) the fender. A positive poke change means the wheel moves outward (more aggressive). The matching inner change tells you whether the back of the wheel moved closer to the suspension or further away. Our calculator shows both, in millimeters and inches.
Need Expert Wheel Fitment Advice?
Our Denver team specializes in custom wheel fitment. We’ll help you find the perfect offset, width, and setup for your vehicle. Free consultations available.