Many topics can be derived around car wheels, such as the wheel materials we discussed earlier and wheel maintenance, among others. We can learn even more about wheels!

For friends who modify wheels or upgrade tires, a key concern is wheel parameters. When talking about wheel parameters, we cannot avoid size, width, PCD & bolt pattern, offset, and center bore.

Size

When we talk about wheel size in daily life, we actually refer to the wheel’s diameter. Generally, the most common mainstream wheel sizes we encounter daily are 14-inch, 15-inch, and 16-inch.

For the same vehicle model, increasing the wheel size will inevitably require reducing the tire’s aspect ratio. As we mentioned when discussing tires before, tires with a lower aspect ratio have a smaller slip angle caused by the deformation of the soft tire sidewall during cornering. This results in more accurate vehicle steering, faster response, richer road feedback to the driver, and a more direct handling feel. However, on the flip side, ride comfort will definitely decrease, and the ride will feel stiffer. At the same time, larger wheels can accommodate larger-diameter brake discs and calipers, leading to stronger braking force.

Nevertheless, larger wheels also bring disadvantages such as increased weight, reduced acceleration, higher fuel consumption, slower suspension response, and compromised driving comfort.

Width

Wheel width is not expressed with numbers like 195 or 205 (as tires are). It is commonly known as the "J value," and its size directly affects tire selection. For tires of the same size, different J values require different tire aspect ratios and widths.

Offset

Offset, commonly called the "ET value," is the distance from the inner side of the mounting hole (fixing surface) to the wheel’s centerline.

To put it more simply: after the wheel is installed, does the position of the mounting bolts sit inward toward the car or outward toward the car body?

Offset is not just about whether the wheel looks convex or concave visually; it also affects 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). Going back to the previous point: if the ET value of the modified wheel remains the same but the J value increases, the wheel will protrude outward on both sides. For example, if the original wheel is 6J and you modify it to 8J, the wheel will protrude outward by a distance of (8J - 6J) × 2.54CM / 2 = 2.54CM (8J means the wheel width is 8 inches, and 1 inch = 2.54CM). For this protruding part, you need to check if it will rub against the car’s shock absorbers, suspension, etc.