What Is My Wheel's Offset?To find the offset, start by determining the wheels' centerline. To obtain that, first measure the wheel's overall width from one outside edge to the other. Do note, that's not necessarily the same as the width given in the manufacturer specs. For example, the width in 20x8.5 inches refers to the distance between the inner flange and outer flange. Next, divide the width in inches by 2 to find the centerline. The width of this wheel is 9.5 inches, so its centerline is at 4.75 inches. Then, subtract the centerline value from the backspace value to find your offset in inches (5.25-4.75=.5). If the resulting number is negative, then your offset is negative, and the opposite goes for a positive offset. If the centerline value and backspace are the same, then the offset is zero. Don't forget, this number is still in inches. To convert, multiply it by 25.4 to get the offset in millimeters. The offset of this wheel is +.5 inch or +12.2 mm. Our result is a few millimeters from the manufacturer's listed offset. We tried to illustrate the offset in the photo that shows the two lines drawn on a straightedge, which indicates the position of the wheel's mounting surface to its centerline. We recap the equations we used to get backspace and offset in the following quick equations.
What Do Positive and Negative Look Like?Negative offset configurations are often found on lifted trucks and look badass. On the other hand, negative offset on a lowered truck can look just plain bad. Take a look at these three trucks. A lifted one's offset can make the wheels stick out-in order to clear those big tires.
The lowered pickup's positive offset wheels look tucked from the side and clean from the front. | 
Another way to see positive and negative is through the often-seen negative camber, which occurs when the top of the wheel tucks in toward the vehicle and the bottom juts outward. |
If you put the wrong wheels on this ride, the negative offset will make the wheels stick out, and you will have a lowrider. | |