Pull the measuring tape out before using it to inspect it for bends or dents. If the measuring tape is damaged, you won’t get accurate measurements.
The lips are the portion of a rim that stick out around the edge of the barrel. They help hold a wheel in place while a vehicle is in motion. The outer diameter only refers to the rim’s measurement from lip to lip. The true diameter of a wheel doesn’t include the lip.
The barrel refers to the flat surface in the middle of a rim’s width. This is where the wheel rests when it is installed on a rim.
You can measure from the inside of the lip to the opposite edge if you’d like, but this can be hard to do since the measuring tape won’t be perfectly flat across the surface of the rim.
Wheel widths are typically sized in 0. 5 in (13 mm) increments, so if you get a number that doesn’t end in a full or half inch, check your measurements again. It is unlikely that your rim’s width ends in a number that isn’t 0 or 5.
Bolt pattern measurements are typically taken in millimeters. Bolt patterns are written with 2 measurements: the number of bolts and the diameter from center to center. So a 4x100 bolt pattern means that there are 4 lugs, with a diameter of 100 millimetres (3. 9 in).
It doesn’t matter which of the bolts on the opposite side you choose to use.
The mounting face refers to the backside of the center of a rim where your bolt pattern is. It faces the brake disc on a wheel. If the wheel has no (or zero) offset, then the back of the mounting face is in the center of the rim. If the mounting face is behind the center of the wheel, then it has a negative offset. This is common on older vehicles and exotic vehicles. If the mounting face is in front of the center of the wheel, then the rim has a positive offset. This is the most common configuration for rims, since it creates more space for the brakes and provides greater stability.
Measuring offset and backspacing can be kind of tricky. Write down and label each measurement on a piece of paper to make this process easier.
The measurement from the edge of the inside mounting face to the edge of the inside wheel is the backspacing.
For example, let’s say you have a rim with a 9 in (23 cm) width. The center of the rim must be 4. 5 inches (11 cm). If the backspace is 6 inches (15 cm), then you subtract 4. 5 from 6 to get 1. 5 inches (38 mm). Because this number isn’t negative, the rim has a positive offset. Offset and backspacing will help you determine brake clearance on a rim. Measure a brake disc from edge to edge to determine how much space it needs in a wheel well.
