What is Offset in Mags? Complete Guide to Wheel Offset and Backspacing

Custom wheels and tires can transform a vehicle’s appearance and handling — but only if the wheel offset and backspacing are correct. In this guide, we explain wheel offset and backspacing in detail, including how to measure them, why they matter, and the risks of incorrect fitment.

Understanding Wheel Offset: Definition and Types

Wheel offset describes the distance between the hub mounting surface and the centerline of the wheel. This determines how the wheel sits inside the wheel well and affects clearance, handling, and safety.

• Zero Offset: The hub mounting surface aligns exactly with the wheel’s centerline.
• Positive Offset: The hub mounting surface is closer to the outer (street) side of the wheel. Common in front-wheel-drive and modern rear-wheel-drive vehicles.
• Negative Offset: The hub mounting surface is closer to the inner side of the wheel, making the wheel stick out farther from the vehicle. Typical for deep-dish wheels and some off-road vehicles.

Wheel Offset Reference Table

What is Backspacing and Why It’s Critical

While offset refers to the hub-to-centerline distance, backspacing measures the distance from the hub mounting surface to the inner edge of the wheel. This determines how much space remains between the back of the wheel and suspension components.

Backspacing is particularly important when upgrading to wider wheels or tires. Too much backspacing can cause the inner edge of the wheel or tire to rub against suspension parts, brake calipers, or the inner fender.

Risks of Incorrect Wheel Offset

Incorrect wheel offset can cause serious issues for vehicle performance and safety. Below are the most common problems for excessive positive or negative offset:

Problems with Too Much Positive Offset

• The inner edge of the wheel or tire rubs against suspension or brake components.
• Damage to tires, fenders, or suspension arms.
• Impaired steering response and reduced stability.
• Increased wear on bearings and brake parts.

Problems with Too Much Negative Offset

• Wheels and tires extend beyond the fenders, exposing them to damage.
• Increased steering wheel kick-back.
• Higher stress on suspension components.
• Reduced cornering ability and stability.

How to Measure and Choose the Correct Offset

When selecting aftermarket wheels, it is critical to match the offset within ±5mm of the original equipment specifications if possible. Here’s a step-by-step guide:

1. Check OEM Specifications: Consult your owner’s manual or manufacturer’s data for the recommended offset and backspacing.
2. Measure Wheel Width: From bead seat to bead seat, not outside lip.
3. Measure Existing Offset: Usually stamped on the inside of the wheel, noted in millimeters (e.g., ET40 = +40mm).
4. Account for Tire Width: Wider tires may require an adjusted offset to maintain clearance.
5. Test Fit if Possible: Before mounting tires, test fit the wheels to check clearance on all sides — suspension, brakes, and fenders.

Wheel Offset and Vehicle Handling

Proper offset is not only about fitting the wheel in the well. It also impacts the vehicle’s dynamics:

• Too much positive offset narrows the track width, reducing cornering stability.
• Too much negative offset widens the track excessively, increasing drag and suspension stress.
• Incorrect offset can lead to unpredictable handling and uneven tire wear.

Best Practices for Upgrading Wheels and Tires

• Always verify both offset and backspacing when moving to larger or wider wheels.
• Use a reputable tire and wheel shop to measure and recommend the correct fitment.
• Ensure that the load rating of the wheels matches or exceeds vehicle requirements.
• Keep in mind that even a visually acceptable clearance may cause problems under suspension compression or full steering lock.

Conclusion

Selecting wheels with the correct offset and backspacing is essential for ensuring safe, efficient, and visually appealing wheel fitment. It maintains clearance, preserves handling characteristics, and prevents costly damage to the vehicle. Always prioritize accurate measurement and professional advice when customizing your vehicle’s wheels and tires. Learn more about offsets and know your vehicle at KGCAR.PH.