How is the wheel size measured?
2 Answers
Wheel size does not need to be measured; it can be determined by checking the parameters. Here is a detailed explanation: 1. Wheel size consists of two parameters: rim diameter and rim width. 2. The representation can be in formats like 15*6.5; 15*6.5JJ; 15*6.5J, etc., with no strict requirements on the format. 3. The number "15" at the front indicates the rim diameter, meaning the rim diameter is 15 inches; the "6.5" (or 6.5J, 6.5JJ) at the back represents the rim width, indicating the rim width is 6.5 inches. The wheel size can usually be found engraved on the back of the wheel. Here are other parameters of car wheels: 1. PCD: Refers to the Pitch Circle Diameter of the bolt holes. The representation is like 5*114.3, 10*100/114.3, where "5" indicates the number of bolt holes, meaning there are 5 bolt holes. "114.3" indicates the Pitch Circle Diameter of the bolt holes is 114.3mm. 2. Offset: The distance between the mounting surface and the centerline of the wheel, which can usually be found on the back of the wheel. The offset is used to adjust the wheel track and ensure the wheel does not interfere with the car body. 3. Center Bore: The large hole in the middle of the wheel. Note that the center bore size should be measured from the back for accurate data, and it varies from car to car.
When I first started with car modifications, measuring wheel dimensions was really tricky. The wheel diameter is the distance from the center to the outer edge of the wheel, and I used a tape measure to go around and divide by π to confirm if it was 16 inches. The width is even more critical—measure the inner width of the wheel, for example, a 7-inch width must match the tire size. The bolt pattern was tricky: I counted 5 holes, then used a caliper to measure the distance between the centers of each hole to avoid mismatching the hub. The center bore size also needs its diameter measured—if it's too small, it won’t fit the axle. The offset was my biggest lesson; not measuring it accurately caused the new wheels to rub against the fender after installation, forcing me to redo it. Now, I always check the vehicle manual first, then take physical measurements. With simple tools, you can get it right and save money. A few more practices, and it becomes second nature.
