With so many different numbers and measurements on wheels, it can be a little confusing to understand.
Today, we'll go over offset and backspacing.
So you’ve managed to save up the cash to start building your truck. First things first, you end up searching the internet trying to find your bolt pattern, backspacing, hub size, and more. But more importantly, you’re trying to figure out what wheels and tires are going to fit your truck. Does diameter matter? Does width matter? Unfortunately, it’s just not that easy. Things like backspacing and offset can be as unique as the wheel that matches your truck. So how can you be sure what you want will fit and look exactly how you want it to? That’s where we come in.
Wheel sizes are normally listed as 22x12 -51mm or 18x9 +25mm, etc, but what do all of those numbers even mean?
The first number listed is the diameter in inches. So a 22x12 -51mm would be a 22” diameter wheel.
The second set of numbers listed is the width in inches, so a 22x12 -51mm would be a 12” wide wheel.
The third set of numbers is where it gets tricky. That number is the offset of the wheel in mm. So a 22x12 -51mm would be a -51mm offset.
So there’s wheel diameter, wheel width, and a “positive” or “negative” offset. What is offset? Offset is the distance in millimeters (mm) + or - from the hub (where you bolt the wheel to the vehicle) to the true center of the wheel.
A “negative” offset is where the mounting surface of the wheel is closer to the inside (brake side) of the wheel. In the truck world, many custom truck wheels come in aggressive negative offsets. The more negative the offset, the more aggressive stance you will get. This means the wheels will “poke” outside of the fenders. “Poke” or “Stance” is when the wheel and tire stick outside of your fender. A negative offset is what can create a larger lip or concave style, which will push the tire out.
A “positive” offset is where the mounting surface of the wheel is closer to the outside (fender side) of the wheel. This pushes the wheel in toward the brakes which can “sink” the tire and wheel into the fender well opening.
Does backspacing matter? Backspacing is similar to offset, but it changes where we measure from. We are still looking for the distance from the mounting surface of the wheel, but instead of measuring the “center line”, it’s measured from the back edge of the mounting surface (hub). Backspacing is less commonly used than offset because offset has replaced backspace measuring in common wheel fitment.