May 15, 2021
In short, offset is the distance from the center line of your wheel to the mounting pad. If the mounting pad is closer to the face of the wheel from the center line the wheel is a positive offset, if the mounting pad of the wheel is at the dead center of the center line the wheel is a zero offset and if the mounting pad of the wheel is closer to the backside of the wheel from the center line the wheel is considered a negative offset wheel.
The easiest way to understand how the offset affects your fitment is, the higher the offset the closer the wheel is to your chassis and the lower the offset the further the wheel is from your chassis.
No vehicle has a set number that they require, every vehicle has a minimum and maximum offset tolerance they can use. It is very important that the wheels you choose are within that minimum and maximum offset range to prevent fitment issues.
Let’s say you have a car that requires a minimum offset of 35 and a maximum offset of 45, If you attempt to install a wheel that’s a 25 offset you run the risk of your tires rubbing on your fenders and or the wheels and tires sticking out. And if you attempt to install a wheel that’s a 50 you run the risk of the wheel obstructing with your suspension components.
Trucks are a little more flexible as they tolerate a wider minimum and maximum range, specifically lifted trucks. As an example for trucks let’s say you have a minimum offset of 0 and a maximum offset tolerance of 12.
If you’re wanting for the wheels to stick outside of your fenders you’d want to look for a wheel with an offset lower than your minimum tolerance of 0. If you want the wheels to stick out the least or not stick out at all aim for options closer to your maximum tolerance of 12.
We’re often asked if running a negative offset will come with problems. Here’s my opinion on the topic, If the offset is too negative and you’re running an oversized tire, I’d say you have a high chance of encountering problems.
When your vehicle was manufactured the suspension components, hub and bearings were all made to specifically tolerate your original equipment wheel and tire weight and overall geometry. These components do offer a little tolerance for plus sizing however not when it’s an extreme.
So let’s say your truck comes with a 31 inch tire from factory and you lift the truck and jump up to a 35 inch tire. The tire is going to weigh more than your factory tires. This upgrade will cause some strain to the drivetrain which can be resolved by regearing your ring and pinion but not always is that required.
When can problems arise from a negative offset?
Let’s say you now take that already borderline fitment and use a super low offset to hang it out the fender. You’re now increasing the overall strain as your vehicles hub and wheel bearings will suffer being that the wheel and tire geometry has now changed and your factory hub and wheel bearings weren’t designed to support the additional weight.
Think of it like this, if you hold an apple in your hand and close to your body you can do so for an extended period of time with minimal strain, now imagine holding a watermelon with one hand with your arm fully extended horizontally to your side.
You can definitely plus size your wheels and tires to where they can hang outside your fenders safely with minimal strain but there is a very fine line to those limitations and we always recommend that you consult with an expert to determine what that fine line is.
When measuring your wheel offset you’ll need to know a couple things:
Warning: This can be slightly confusing, if you know your wheels width you’re welcome to use our wheel offset calculator for a more simplified solution.
Now that you know your wheels width, backspacing and centerline we can calculate your offset.
Centerline – Backspace = Offset
To convert inches to millimeters, multiply inches by 25.4 & to convert millimeters to inches, divide mm by 25.4
In Example: Let’s say your wheels is 10 inches wide, your centerline is 5 inches. For this example let’s say your backspace is 4 inches. 5 – 4 = 1 and 1 inch in millimeters is -25.4 so this means your wheels offset is -25mm (always round). In the case where the backspace is higher than your centerline your offset is positive.
In the above section we learned about backspacing thru the necessity of having to measure for the offset. If you skipped that section, the backspace of a wheel is the distance from the outer edge of the wheel to the mounting pad. While the offset of the wheel is the distance from the centerline of the wheel to the mounting pad.
Traditionally it was common to reference only backspacing as all the vehicles manufactured at the time required low offset wheels so it was easier to reference the backspacing. In 1984 Chevrolet introduced the C4 Corvette which was possibly one of the first american vehicles to require high offset wheels.
By this point the wheel manufacturers would stamp on the mounting pad the offset and begin to use the offset term as a primary reference. The stamp would like something like this 8.5Jx17 ET35 where the offset is referenced as ET which is the German word EinpressTiefe meaning offset.
By the 1990s more vehicles were being manufactured that required high offset wheels and the term offset begun to gain traction over backspacing.
As of today backspacing and even front spacing are truly the most important variables in custom wheel manufacturing where a precision fitment is a must.
However for the cast wheel industry and a greater portion of the factory and aftermarket wheels being produced offset is going to be the measurement primarily referenced.