Size

Wheel size refers to the diameter of the wheel. We often hear terms like "15-inch wheel" or "16-inch wheel"—the numbers 15 and 16 here represent the wheel size (diameter). Generally, for passenger cars, larger wheel sizes with higher tire aspect ratios create a visually striking effect and enhance vehicle handling stability. However, this is accompanied by a side effect: increased fuel consumption.

Width

Wheel width is commonly known as the "J value." It directly affects tire selection. For tires of the same size, different J values require different tire aspect ratios and widths.

PCD and Bolt Pattern

PCD, or Pitch Circle Diameter, is the diameter of the circle formed by the center of the wheel’s fixing bolts. Most wheels have either 4 or 5 bolts, and the distance between the bolts varies. Hence, we often see designations like 4X103, 5X114.3, or 5X112. Taking 5X114.3 as an example, it means the wheel has a PCD of 114.3mm with 5 bolts. When selecting wheels, PCD is one of the most critical parameters. For safety and stability, it is best to choose wheels with a PCD that matches the original vehicle’s for upgrades.

Offset

Offset, commonly called "ET value," is the distance between the wheel’s bolt mounting face and its geometric centerline (the centerline of the wheel’s cross-section). Simply put, it is the difference between the center of the wheel’s bolt hub and the center point of the entire rim—colloquially, it determines whether the wheel sits inward or outward after modification. For most passenger cars, the ET value is positive; for a few vehicles and some SUVs, it is negative. For example, if a car has an original ET value of 40, installing a wheel with ET45 will make the wheel sit more inward within the wheel arch visually. Beyond visual changes, the ET value is also related to the vehicle’s steering characteristics and wheel alignment angles. A significantly mismatched ET value may cause abnormal tire wear, accelerated bearing damage, or even make installation impossible (due to friction between the brake system and the wheel preventing normal rotation). In most cases, wheels of the same style from the same brand offer different ET values. Before modification, comprehensive factors should be considered. The safest approach, without modifying the brake system, is to keep the ET value of the modified wheel the same as the original.

Center Bore

The center bore is the part that connects and secures the wheel to the vehicle. It is the concentric circular area at the center of the wheel. The diameter of this bore determines whether the wheel can be installed with its geometric center aligned with the vehicle’s hub center. Although wheel spacers can adjust the bolt pattern, this type of modification carries risks, and users should proceed with caution.