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If you are a novice when it comes to cars, many times, you will find yourself clueless about the terms that you are hearing, especially when you are talking to a mechanic. Among others, you will often hear about wheel offset, especially when you are asking help from the pros for a tire change.
If you want to know what it is and how to measure wheel offset, I got you covered in the rest of this post. The discussions below will let you know why it is important and how to calculate the value of your wheel offset. It might seem quite technical, but if you know how it is computed, you will realize that it is indeed quite simple.
What is Wheel Offset?
Before I let you know how the computations work, let me first give you a quick primer on what is a wheel offset. Once you know what it means, it will be easier to understand why it is important and how it can be measured.
In a nutshell, a wheel offset refers to the distance from the wheel’s hub mounting surface to its centerline. The measurement is expressed in millimeters. The value can be positive, negative, or zero.
Positive Offset: This means that the mounting surface of the hub is in front the wheel’s centerline. A positive offset is common in new rear-drive cars, as well as in most front-wheel drive automobiles.
Negative Offset: This means that the mounting surface of the hub is behind the wheel’s centerline. Deep dish wheels belong to this category of wheel offset.
Zero Offset: This means that the mounting surface of the hub is aligned with the wheel’s centerline.
Aside from knowing what it means, you should also learn about what happens when the offset is too much. That being said, if there is too much positive wheel offset, the inner edge of the wheel can be damaged and the tires can rub against the suspension, which can constitute costly repairs. It can also interfere with the brake. The stability of the car can also be compromised, and hence, will affect safety. Lastly, it can also lead to poor handling.
On the other hand, in case there is too much negative wheel offset, there can be increased steering wheel kickback. The entire suspension can also be subjected to higher stress, which can affect the durability of the components and the overall performance of the car. Similar to too much positive offset, it can also result in poor handling.
Why is Wheel Offset Important?
You might now have a clearer understanding of what is offset, but you are possibly still struggling to understand why it matters. To put it simply, an offset is important because it makes sure that the wheels and tires are right for the vehicle. In the paragraph above, I have noted that will happen if there is too much positive or negative offset.
According to experts, the offset should not be more than five millimeters when compared to the offset of the tires that will be replaced. The wrong offset can compromise not only the performance of the car, but also its looks.
If you will purchase an aftermarket wheel that has the same offset as the one that has been replaced, you can expect that the scrub radius, handling, and suspension will remain the same. On the other hand, if it is wider, clearance can be lost from the side of the suspension.
How To Measure Wheel Offset
Now, let us go to the most important part of this post – the measurement of wheel offset. As a car owner, you might not feel compelled to know how to do it. For the pros, on the other hand, this is important to recommend new wheels that will match the requirements of the vehicle.
In most cases, the manual from the manufacturer will indicate the offset of the wheels. Often, they are also embossed on one part of the wheel. They may come with the letters ET, although such is not the case all the time. For instance, if the offset is 45 mm, it can be written as ET45. If it is not printed, this is the time that you will have to do the measurements manually.
Before you measure the wheel offset, there is one value that you should determine – wheel backspace. To put it simply, wheel backspace is the distance between the mounting plate and the wheel’s flange. This is a combination of the width and the offset of the wheel.
To measure the backspace, start by laying the wheel on a flat and stable surface. See to it that you are facing the back part of the wheel. Use a straight edge and lay it on the wheel’s inboard flange. Use a tape measure or ruler to determine the distance between the inboard flange and the straight edge. Expressed in inches, this is the distance from the wheel’s inside lip to the mounting surface of the hub.
Now that you have the value of the backspace, you have to know the width and the centerline of the wheel. To compute the centerline, measure the distance from the outboard to the inboard flange (which is the width of the wheel) Let us say that the width is eight. If you divide it by two, this means that the centerline is four.
To compute the wheel offset, all that you have to do is to subtract the centerline from the backspace. If the centerline is four inches and if the backspace is two inches, this means that the offset is negative two.
If the value of the backspace is lower than the centerline of the wheel, you will end up with a negative offset. On the other hand, if the backspace is higher than the centerline, you will have a positive offset. If the backspace and the centerline are the same values, you will have a zero offset. Go back to the discussions above to know more about this.
If in case you do not have the right unit of measurement, remember this – if you want to convert inches to millimeters, all that you have to do is multiply the value by 25.4. On the other hand, to convert millimeters to inches, you have to divide the value by 25.4.
Other Things to Remember
Aside from knowing how you can take the right measurements, you also have to keep these things in mind:
- If you have a wheel with the wrong offset, this is not a hopeless case. You might want to consider the possibility of using offset spacers. The latter are metal shims with a bolt. It has the primary purpose of pushing the wheel from the suspension, which is one way of correcting the offset.
- When using spacers, one of the most important things to do is to make sure that it is hub-centric. This means that it should have a precise fit on the axle hub of the car. This will provide the assurance that it will be able to properly hold the weight of the car.
- In most instances, it is not enough that you compute the wheel offset. A better thing to do is to test fit the wheels, which will be an opportunity for you to see if they are suited for your car.
- Changing the wheel offset of your car is also necessary if you want a change in aesthetics. It gives the car a wider and more aggressive stance. Nonetheless, this should be done with caution as changing the offset without a solid basis can affect the car in more ways than one.
- The right offset is not the only thing that should matter. You need to make sure that the tires have top-notch quality, especially in terms of construction and the materials that are used. A separate post is needed to tackle the most important considerations when you are searching for aftermarket tires and wheels.
At this point, I hope that you already know how to measure wheel offset. The term might sound technical, but as shown above, the computation is pretty much easy. You just have to know the basic values and you can easily determine the offset, which will be vital in looking for new aftermarket wheels.