What does wheel offset mean?
3 Answers
Wheel offset refers to the distance from the inner mounting surface (mounting face) of the wheel to its centerline, which can be categorized as positive offset, negative offset, or zero offset. Characteristics and applications of negative offset: Negative offset means the mounting face is positioned inward (toward the brake system) relative to the wheel centerline. "Deep-dish" style wheels often have negative offset, commonly seen in SUV models and some BMW vehicles. Characteristics of zero offset: Zero offset means the two surfaces coincide. Characteristics and applications of positive offset: Positive offset means the mounting face is positioned outward. Wheels with positive offset are typically used in front-wheel-drive and some rear-wheel-drive vehicles.
I did some research on this ET value issue when I modified my wheels before. Simply put, the offset is the distance between the wheel mounting surface and the centerline. For example, I measured the original wheels, and ET45 means the wheel is recessed inward by 45mm. When changing to aftermarket wheels with a smaller ET value, the wheels will protrude outward, making them look fuller and more stylish. But be careful not to go too extreme—when I changed to ET35 on my car, I clearly felt the wheelbase widened, which actually reduced cornering stability and worsened wet-weather grip. The safest approach is to measure the distance from the original wheel to the fender with a tape measure, calculate the desired protrusion, and then choose the wheels accordingly. This way, you get both good looks and safety.
I remember when I first started restoring classic cars, I got burned by the ET value. I found a set of beautiful wheels, but after installing them, I realized the tires were rubbing against the brake calipers. Actually, the offset is the distance between the wheel's mounting surface and its centerline—the smaller the number, the more the wheel sticks out. A mechanic taught me to use a steel ruler placed vertically against the brake disc to measure the distance to the wheel edge. The stock ET was 50, and the ET38 wheels I installed protruded 12mm more. Always check the factory specs before modifying—rear wheels have more space and can handle a few extra millimeters, but you need to be careful with the front wheels. Now, I always bring calipers when shopping for wheels, since wheels sticking out too far can rub the suspension, and sitting too inward can still interfere with the brakes.
