What is the ET value of a tire?
4 Answers
Tire ET value refers to the offset, which is the deviation between the mounting surface of the wheel hub and the centerline of the rim, measured in millimeters. It can be positive, zero, or negative. The ET value is defined as the distance between the mounting surface of the rim and the center of the rim. A positive value indicates an outward direction, while a negative value indicates an inward direction. Tires are circular elastic rubber products mounted on various vehicles or machinery, typically installed on metal rims. They support the vehicle body, absorb external shocks, ensure contact with the road surface, and maintain driving performance. Tires are often used under complex and demanding conditions, enduring various deformations, loads, forces, and extreme temperatures during operation.
After years of modifying cars, I've learned that the ET value of a tire is actually the distance from the mounting surface of the wheel hub to the centerline of the rim, measured in millimeters. This number directly affects the position of the wheel within the body: a smaller ET value makes the wheel protrude more visibly, giving a fuller look but potentially causing rubbing against the wheel arch; a larger ET value tucks the wheel inward, creating a concave appearance. Those into stance modifications love tweaking this, but doing it poorly can affect steering and suspension geometry, even accelerating bearing wear. I recommend checking the factory data before changing the ET value—keeping the deviation within plus or minus 5 millimeters is safer, and always consider the changes in tire width together.
I just learned about ET value when changing my wheels. Simply put, it's the wheel offset measurement that directly determines whether your tires will rub against brake calipers or fenders. The ET38 wheels I chose this time extend 7mm further out compared to the stock ET45, perfectly flush with the fenders when paired with 235 tires - no more strange noises when cornering. Note that increasing ET value narrows the track width, potentially reducing high-speed stability; while decreasing ET improves stance but requires extra caution against tire rubbing on inner liners over bumps. Wheel selection isn't just about looks - ET values must match your vehicle's specifications.
As an auto mechanic, I often encounter issues caused by customers randomly altering the ET value. The ET value is like the ID number of a wheel, stamped on the back of the rim. Once, a customer switched to off-road rims with an ET20, and during a turn, the tire directly wore through the ABS wiring harness. The original factory design takes into account the wheel track, suspension travel, and steering angle. Changing the ET value without proper consideration is like wearing ill-fitting shoes—short trips might be manageable, but long journeys will inevitably lead to problems. If modifications are necessary, be sure to measure the minimum clearance from the center of the original rim to the suspension and leave at least a 10 mm buffer space.
