The wheels are much more important than people give them credit, and there are a number of reasons why you should know how to measure the wheel size properly. Aside from knowing what size tires you’ll need for your car, wheel size is important if you plan on replacing your wheels with aftermarket ones.
In this article, we’ll cover the most common aspects of wheels, and which dimensions are important factors to take into consideration. We’ll also show you how to properly measure wheels.
What Can You Measure On A Set Of Wheels?
As we’ve already mentioned, there are more things to measure on a wheel aside from its diameter. Some measurements are more important than others, but to make the right choice when buying aftermarket wheels, you should be aware of all these measurements and what they mean.
The first thing to know is the wheel diameter. It’s basically the size of the wheel and knowing the diameter is important for finding the right tire size. Aside from the wheel diameter, you should know the width as well. The wheel diameter is most commonly referred to in inches, and the most common wheel sizes are between 15 and 19 inches, while luxurious and performance cars may have a larger wheel fitted. The diameter and width of a wheel are related to the tire size you need to choose.
When looking for aftermarket wheels, offset is another factor to take into consideration. The wheel offset measures the distance between the hub surface and the wheel’s center. Depending on the wheel, the offset can be positive, negative, or zero. Contrary to popular opinion, positive offset means that the mounting hub is pushed toward the face of the wheel. This means that wheels with more positive offset will be more tucked under the fenders.
A negative offset means the opposite. It’s less common than a positive offset, but there are aftermarket wheels with a negative offset as well. This means that the mounting hub is pushed more toward the suspension, making the wheel stick on more. Zero offset means that the mounting hub is located exactly at the center of the wheel.
Offset is extremely important because in some cases, wheels won’t fit your car, even if the width and diameter are right. If the wheel is tucked under the car, it’s likely that suspension or brake components will interfere with fitment. In this case, wheel spacers can be used to push the wheels so they would fit properly.
The bolt pattern is another extremely important aspect of wheel measurement. Each car model has a specific bolt pattern consisting of two numbers. The first number represents the number of bolts or studs, while the second number represents the diameter of the circle formed by those bolts or studs.
For European cars, a great example would be 5×120 (the bolt pattern for most BMWs), while North American cars have a slightly different pattern example – 4×4.5. For European vehicles, the second number is represented by millimeters, while for North American cars the number is represented in inches.
Just like cars have different bolt patterns, wheels are also made according to these bolt patterns. It’s safe to say that the most popular bolt patterns have the largest variety of wheel options.
The center bore is also worth mentioning although it’s one of the things that can be modified to fit. Different vehicle models have a different size center bore, and for safety reasons, the center bore should be the same on both the hub and wheel.
Step-By-Step Guide To Measuring Wheels
Measuring wheels isn’t a complicated process, however, it does require removing the wheels from the car and the tires from the wheels. Removing the wheels from the car is a straightforward process, however, removing the tires from the wheels requires special tools and will need to be done by professionals.
Once you’ve removed the wheel and tire, you’ll need to place it on a flat surface. By placing a tape measure across the center of the wheel, you’ll need to measure the diameter of the inside part of the barrel. This is the actual diameter of the wheel. If you measure the entire wheel, you’ll get the overall wheel diameter which is usually around an inch and a half larger.
Measuring the wheel width is done similarly. The tape measure should be placed inside the barrel, instead of measuring the entire width. The common thing about measuring wheel diameter and width is that you need to measure points where the tire is placed.
The wheel offset, or ET as many call it, is measured differently. You’ll need to turn your wheel and place it face-first on the ground. Make sure you do this gently because some wheels are prone to scratches and scuffs. You’ll need a comprehensive level measuring tool placed on top of the center of the wheel and measure the length between the tool and the mounting hub. The difference between the measured distance and half the width of the wheel is the offset. Although most wheels have the offset or ET written down inside of it, it’s a good thing to know how to measure it in case it’s missing.
Lastly, measuring the center bore doesn’t require any special tools, and is done simply with slide calipers. You can use a tape measure as well, but being as precise as possible is important to fit the wheel properly to your car. The center bore should be measured to the precision of a tenth of a millimeter.
Conclusion
It’s no secret that all the possible information about wheels and tires for almost every vehicle on the road is available online, however, for someone interested in cars, how they work, and genuinely knowing more than the average driver, these measurements will mean a lot. Knowing how to measure wheel size is important if you plan on fitting aftermarket wheels and tires to your car, and fitting them for the best look and performance capabilities.