How to Measure Wheel Sizes
If you are unsure the overall size of your wheels, there are a few things to consider when attempting to measure the dimensions. You will want to find the following:
- Bolt Patterns
With the Wheel Diameter, keep in mind that there are two measurements to consider: Overall Wheel Diameter and Actual Wheel Diameter.
When measuring for the Overall diameter, you will want to measure from the outside lip to outside lip of the wheel (Shown by the Green Line in the photo below).
When measuring for the Actual Diameter, you will want to measure from the inside of the Barrel of the wheel (Shown by the Red Line in the above photo). Example: A wheel with an actual Diameter of 18” will have an overall diameter of around 19.5”.
Measuring the Wheel width is similar to measuring the Diameter. You will want to measure from the Barrel Section and not to overall outside width (See Picture Below).
The offset of a wheel is the distance from the hub mounting surface to the center line of the wheel. This is an important measurement to keep an eye on when choosing your next set of Mustang wheels. The wheel offset is measured in millimeters and results in three different types of offsets.
The Three Types of Offset
- Positive Offset: The hub mounting surface is toward the face of the wheel.
- Negative Offset: The hub mounting surface is toward the back of the wheel.
- Zero Offset: The hub mounting surface is even with the centerline of the wheel.
The backspacing is the distance from where the hub section of the wheel contacts the hub surface of the car to the back lip of the wheel (See picture below). Backspacing is always measured in inches and is closely related to the offset so that means when you change one it immediately affects the other.
This is extremely important because it determines the clearance of the wheel in the wheel well. Also, it affects how much the wheel will stick out past the fender. You can measure a wheel’s backspacing by running a straight edge across the rim bead (without a tire) and dropping another straight edge or Tape measure/ruler down to the wheel face, measuring that distance. (See picture below)
The bolt pattern consists of two numbers and looks like this: 5×4.50. The first number in this example(5) indicates how many bolt holes or studs are on the vehicle while the other number (4.50) describes the diameter of the circle formed by those 5 holes or studs. They are listed in either inches or millimeter units (4.50 is inches). Another example: a bolt pattern of 4×100 indicates a pattern with 4 lugs on a circle with a diameter of 100mm.
Using these tools, you will be able to find the overall dimensions of the wheels you have! Many wheel manufacturers will also have the Diameter and Width Cast in the back of the wheel (example: 17x9) to make it easy to know the main size.
Source: Discount Tire