Calculator
Wheel offset and backspacing
Enter the new wheel and your stock wheel. You get backspacing, how far the outer lip moves, how far the inner lip moves, and the stance that lands in.
- Backspacing
- 4.79"
- Poke vs stock
- +87 mm
- Inner lip moves
- -37 mm
Aggressive
fine on most vehicles
Aggressive: the outer lip sits well past the fender. Expect trimming or rubbing at full lock unless the truck is lifted.
How to read the numbers
A wheel has three numbers that decide where it sits: diameter, width and offset. Diameter decides which tires fit on it. Width and offset together decide where the tire sits in the wheel well. The calculator above does the arithmetic the hard way so you do not have to.
Poke vs stock is the useful one. It is how many millimeters the outer edge of the new wheel sits past the outer edge of your factory wheel. Zero means the new wheel's lip lands exactly where the old one did. Positive means it sticks out further; negative means it tucks in. The stance names, tucked, flush, slight poke and aggressive, are the same ones every fitment gallery uses, so you can go look at photos of the number you just got.
Inner lip moves is the one people forget. Go wider with a high positive offset and the inside of the wheel crowds the strut and the upper control arm. That is why a 20x10 +35 can be a worse idea on a truck than a 20x10 -18, even though it looks tamer.
Stock numbers live on every fit guide; pick your vehicle on any page and this calculator fills them in. When you have a combination you like, the package builder adds the tire and the lift and predicts the rub.
Questions people ask
- What is wheel offset?
- The distance in millimeters from the wheel's mounting face to its centerline. Positive offset pushes the wheel in toward the suspension; negative offset pushes it out toward the fender. Most trucks come from the factory around +20 to +45; aftermarket off-road wheels run from +1 down to -44 and beyond.
- What is backspacing?
- The distance from the mounting face to the inner edge of the wheel, in inches. It is offset and width combined into one number: backspacing = (width + 1) / 2 + offset / 25.4. Older off-road wheels are often sold by backspacing instead of offset.
- Does a lower offset make the wheel stick out more?
- Yes. Every millimeter of lower offset moves the whole wheel outward one millimeter. Going wider also moves the outer lip out by half the extra width, so a 20x10 -18 pokes far more than a 20x9 +1 even though the offset difference is only 19 mm.
- How much poke before it rubs?
- It depends on tire width and lift more than the wheel alone. As a rule of thumb, up to about 15 mm past stock is flush and rarely rubs; 15 to 40 mm is slight poke and may touch the fender liner at full lock with a wide tire; past 40 mm expect trimming unless the truck is lifted. The package builder runs the exact combination.
- Is positive offset safe on a wider wheel?
- Wider wheels with high positive offset move the inner lip toward the strut, upper control arm and brake caliper. The calculator's 'inner lip moves' number shows that; past roughly 15 mm, check clearance before buying.