What is Wheel Offset?
Wheel offset is one of the most important measurements when selecting wheels for your vehicle. It refers to the distance from the wheel's hub mounting surface to the centerline of the wheel. This measurement is typically shown in millimeters and is marked as "ET" (from the German "Einpresstiefe" which translates to insertion depth).
Understanding offset is crucial because it determines how far the wheel will sit inside or outside the wheel well. The wrong offset can cause rubbing issues, affect handling, and even put stress on suspension components.
Understanding ET Numbers
The ET number you see stamped on wheels (e.g., ET45, ET35, ET+20) tells you exactly how the wheel will position relative to the hub face.
A typical wheel might show "ET45" which means the mounting surface is 45mm from the wheel's centerline toward the outside of the wheel. This measurement is critical for determining wheel fitment and should match or be close to your vehicle's factory specification.
When shopping for wheels, you'll often see the offset listed in the specifications. For example, a wheel listed as "18x8.5 ET35" means it's 18 inches in diameter, 8.5 inches wide, with a 35mm offset.
Positive vs Negative Offset
Positive Offset (ET+): The mounting surface is toward the front (street side) of the wheel. This is the most common type found on modern vehicles, especially front-wheel drive cars. The wheel sits more inward, closer to the suspension components.
Zero Offset (ET0): The mounting surface is exactly at the wheel's centerline. This creates a completely neutral position and is commonly found on some trucks and older vehicles.
Negative Offset (ET-): The mounting surface is toward the back (brake side) of the wheel. This pushes the wheel outward from the vehicle. Deep-dish wheels and many off-road wheels feature negative offset, creating that aggressive, wider stance look.
How Offset Affects Fitment
The offset you choose has significant implications for your vehicle:
Suspension Clearance: Lower offset (more negative) pushes the wheel outward. While this can look aggressive, it may cause the wheel to rub against the fender or require fender modifications.
Brake Clearance: Higher offset (more positive) brings the wheel closer to suspension and brake components. Going too high can cause clearance issues with calipers.
Steering Feel: Changing offset affects the scrub radius, which can alter steering feel and feedback. Significant changes may cause the steering wheel to pull or create additional wear on components.
Load Distribution: Proper offset ensures the load is distributed correctly through the wheel bearings. Extreme offset changes can increase wear on bearings and suspension components.
Choosing the Right Offset
When selecting wheels, consider these guidelines:
Stay Within Range: As a general guideline, many vehicles can accommodate approximately +/- 5-10mm change from factory offset without issues, though this varies by vehicle. Always verify clearances for your specific make and model. Larger changes may require fender rolling, suspension modifications, or other work.
Consider Tire Width: Wider tires paired with the wrong offset can cause fitment issues even if the wheels alone would fit.
Think About Your Goals: Want a flush look? You might need lower offset. Going for a more tucked OEM+ appearance? Stay closer to factory specs.
Measure Carefully: Before purchasing, measure your current setup including clearance to suspension components and fender lips. This helps you understand how much room you have to work with.