What is wheel offset, and why is proper offset important for spare tires?

Wheel offset is a design feature that determines how the vehicle weight is carried by the wheels and tires. Improper offset on a spare tire may put added stress on the vehicle drivetrain and wheel bearings.

If you look at a car from the rear or the front, imagine you could shift the tires inward toward the center of the car or outward away from the center of the car.  Essentially, you now have a good idea of what wheel offset is and what changing it can do. When a carmaker designs a vehicle, ensuring that all four wheels carry the car's weight in a balanced way will determine the offset measurement of the wheels. It is important to note that the correct offset measurement for a particular car will vary depending on how wide the wheels are. 

Wheel offset is typically displayed in positive or negative numbers based on millimeters (MM). This number is calculated by measuring the position of the lateral centerline of the wheel relative to where the wheel meets the vehicle's hub.  The goal is to have the tire tread meet the road in a position under the car that provides the proper load-carrying support. So, a wider wheel and tire will have a different offset measurement than a narrower wheel and tire, yet both can result in proper load-carrying balance.  

Modern Spare takes offset very seriously, and we design our wheels with this in mind. In fact, when designing a narrow space-saving wheel, we could have vastly simplified our design work and eliminated some major design challenges by sacrificing proper offset.

Although our customers may not be familiar with what the proper offset is on a spare tire or why it is important, this critical measurement is worth the added engineering complexity and effort.