How to Read Bolt Pattern Correctly?

Being able to read bolt patterns correctly is an essential skill. If you know how to do that, you can easily pick fitting new wheels for your car. Of course, the bolt pattern is not the only thing that ensures good fitment, but it's one of the most important ones nonetheless.

Key Takeaways:

• Reading bolt patterns accurately is fundamental to selecting the right wheels for your car.
• The number sequence in a bolt pattern comprises two pieces of information: the number of lugs and PCD.
• Never assume two vehicles from the same brand or model line have identical bolt patterns.

Engineers design with particular bolt patterns in mind for a good reason. They control weight distribution and secure the wheel to your vehicle. If you get your bolt pattern a bit wrong, all that careful balance goes out the window immediately.

Thankfully, this is just a skill issue. Reading bolt patterns is very simple. But that's not enough because you need to understand what it really is and how it works.

Matching up the correct wheels to your hubs is not just a nice thing to do. Your safety on the road depends on how well your wheels are attached to the car. Even small discrepancies between the bolt pattern and the post drilled through the hub can lead to wheel detachment or very expensive repairs.

Proper fitment lets you avoid annoying and potentially dangerous things like vibration, wobbling, and issues caused by bad alignment. On the contrary, it guarantees that the wheels are centered well and can respond properly to your handling without damaging performance.

What Do Bolt Pattern Numbers Mean?

Numbers are a crucial element of choosing new wheels. They help you identify how a wheel fits onto the hub of your vehicle. Because your hub already has holes drilled in the correct spots, you just need to find a matching wheel that would fit like a glove.

Normally, there will be 2 essential pieces of information in a bolt pattern number sequence. It contains the number of drilled holes for lugs needed to secure the wheel, hence the other name, lug pattern. And it also has the diameter of the circle in which these lugs sit on a wheel.

This data is also called the bolt circle diameter (BCD) or pitch circle diameter (PCD). It's the diameter of the imaginary circle that passes through the center of each bolt hole.

Both elements help you understand what kind of wheels you need for your hubs. The first one tells you the type by the number of lugs. For example, it could be a 5, 6, or even 8-lug pattern. The number of bolts largely depends on the size of your vehicle and the manufacturer. But generally, the larger the car, the more lug nuts on the pattern. Usually, SUVs and crossovers have 6-lug patterns, while heavy-duty or off-roading trucks often use an 8-lug wheel pattern.

Bolt Pattern Measurement: Metric vs Inches

The same bolt pattern can be written in millimeters or in inches. This can be confusing, and you should always pay attention to the measurement units.

Metric Bolt Patterns

In metric bolt patterns, you measure the distance between the center of one bolt hole to the center of the opposite bolt hole, using millimeters as the unit of measurement. For instance, a bolt pattern of "5x100" means there are 5 bolt holes and the diameter of the circle formed by their centers is 100 millimeters. The first number (5) refers to the number of bolt holes, and the second number (100) indicates the diameter.

Many vehicles produced in Europe and Asia, as well as most modern vehicles worldwide, use metric measurements for their bolt patterns. If you are dealing with cars, trucks, or machinery from these regions, metric bolt patterns are more likely to be used.

Inch Bolt Patterns

In inch-based bolt patterns, you measure the bolt holes' arrangement using inches. For example, a bolt pattern of "5x4.5" means there are 5 bolt holes, and the diameter of the circle formed by their centers is 4.5 inches.

Vehicles and equipment manufactured in North America, especially in the United States, commonly use inch-based measurements for bolt patterns. If you are dealing with American-made cars, trucks, or machinery, inch bolt patterns are more prevalent.

Some classic cars, custom-built vehicles, and performance-oriented applications might still use inch-based bolt patterns. If you are working on vintage vehicles or in specific automotive aftermarket segments, you might encounter inch measurements.

The conversion between metric and inches involves using the appropriate conversion factor: 1 inch equals 25.4 millimeters. Therefore, to convert from metric to inches, you can divide the metric measurement by 25.4, and to convert from inches to metric, you multiply the inch measurement by 25.4.

Here are some common bolt patterns and their equivalents in both metric and inch measurements:

• 4x100 (mm) is approximately equivalent to 4x3.94 (inches)
• 5x114.3 (mm) is approximately equivalent to 5x4.5 (inches)
• 6x139.7 (mm) is approximately equivalent to 6x5.5 (inches)

It's important to use the correct unit of measurement for your specific application, as using the wrong unit can lead to compatibility issues when fitting wheels or other components. Always consult the manufacturer's specifications or guidelines to ensure you have accurate measurements for your bolt pattern requirements.

3-step Guide to Reading Bolt Pattern

There is not much to understand in a lug pattern with only two elements to read. The first one is the number of lugs that has to match the number of holes drilled in the hub. The second number is the diameter of the circle these holes form if you connect them with an imaginary line.

Step one: Identify the Number of Lugs

First, you have to do the obvious thing. And that's count the number of bolts sticking out of your wheel. It can be 4 to 5 bolts for smaller cars and 6 to 8 for larger vehicles. This will be the first number on the bolt pattern specifications.

Step two: Measure the PCD

Measure the pitch circle diameter or PCD. The technique varies slightly for odd-numbered and even-numbered bolt patterns. So, the method is simple for an even-numbered pattern: take measurements from the center of one lug to the center of the opposite lug.

But for an odd-numbered, like a 5-lug bolt pattern, you will need to measure the distance from the center of the starting lug to the back of the third lug in the pattern. Because there are no opposite lugs in an odd-numbered pattern.

A piece of advice is to use a proper caliper, not a ruler. It's much easier, and the numbers are much clearer.

Step three: Cross-reference Measurements with Standard Charts

Especially if you are using a ruler to measure the distance between lugs, you need to cross-reference with a database. This cross-reference of the measurement is essential to ensure accuracy and compatibility.

There are a lot of online databases and automotive manuals that have standard bolt pattern charts for vehicles. You can find information by the make and model of your car or you could just search by the numbers you just got.

How Do You Read a 5-lug Bolt Pattern?

Reading a 5-lug bolt pattern is no different from reading any other lug pattern. The number of lug nuts and the pitch circle diameter allows you to note down the bolt pattern your vehicle needs.

For example, let's take a Honda Civic. It has wheels with five lugs and the diameter is around 114.3mm. That means you will find it written down like 5x114.3. And that's how you should read it.

5 Common Mistakes While Reading Bolt Patterns

Reading bolt patterns is very easy, but it can lead you to experience a sense of false security. Here are just a few common mistakes people make when reading bolt patterns:

• Some bolt patterns are given in inches, while others are in millimeters. Forgetting to convert or misinterpreting the unit can lead to selecting the wrong wheel size.
• Measuring between two lugs is fine for even-numbered patterns. However, for wheels with an odd number of lugs like 5, measuring directly between lugs won't give the correct PCD.
• Assuming the models of the same make have identical bolt patterns. Just because two vehicles are from the same brand or even the same model line doesn't guarantee they'll have the same bolt pattern.
• Relying on the previous owner's word is not always best. Without verification about bolt patterns, you can end up with a set of perfectly mismatched wheels.
• Even with the right tools and methods, human error can creep in. Always double-check measurements for accuracy.