2 Wheel Bolt Pattern Calculator & Guide

This calculator works out the bolt pattern (PCD) of a 2-wheel or 3-wheel vehicle from the number of studs and the distance between adjacent studs. You enter the stud count and the center-to-center distance between two neighboring studs, and you get the bolt circle diameter in millimeters or inches. It’s built for mechanics, DIY builders, and anyone fitting aftermarket rims to a motorcycle, scooter, or ATV.

Formula

The bolt pattern (PCD, or pitch circle diameter) is the diameter of the imaginary circle that passes through the center of every stud. For a regular polygon formed by the studs, the relationship between the side length (adjacent stud spacing) and the circumcircle diameter is:

PCD = d / (2 × sin(π / n))

Where:

• d = center-to-center distance between two adjacent studs (mm or inches)
• n = number of studs (3, 4, 5, or 6 typical)
• PCD = bolt circle diameter (same unit as d)

This formula works for any regular polygon. For a 4-stud pattern, it simplifies to PCD = d × √2, because the studs form a square.

Worked Example

Using the defaults from the calculator: a 4-stud wheel with adjacent stud spacing of 82 mm.

Step 1: Identify n = 4, d = 82 mm.

Step 2: Plug into the formula: PCD = 82 / (2 × sin(π / 4)).

Step 3: sin(π / 4) = 0.7071, so 2 × 0.7071 = 1.4142.

Step 4: PCD = 82 / 1.4142 = 58.0 mm.

So the bolt circle diameter is 58.0 mm (rounded to one decimal). The calculator shows 58.0 mm, and in inches that’s 2.283 in.

When to Use This Calculator

Use this when you have a wheel with an unknown bolt pattern and only a caliper to measure the stud spacing. It’s common when buying used rims, fitting a spare wheel, or adapting a hub for a custom build. The formula works for any number of studs, but 3, 4, 5, and 6 are the most common on motorcycles, scooters, and small trailers.

For 5-stud patterns, the measurement is often taken from the center of one stud to the center of the second-farthest stud (not adjacent), but that’s a different formula. This calculator specifically uses adjacent stud spacing, which is the most reliable and easiest to measure accurately.

How to Measure Stud Spacing Correctly

To get the adjacent stud spacing, measure from the center of one stud to the center of the next stud over. Use a digital caliper for best accuracy. If the studs are threaded, measure from the same side of each stud (e.g., the outer edge of one to the outer edge of the next, then subtract one stud diameter).

For a 4-stud wheel, you can also measure from the center of one stud to the center of the opposite stud and divide by √2, but that’s less direct. The adjacent spacing method is less prone to error because it doesn’t require measuring across a hub.

Common Mistakes

• Measuring from the outside of one stud to the outside of the next – this adds one stud diameter. Always measure center-to-center, or subtract the stud diameter.
• Using the wrong number of studs – a 5-stud wheel with 4-stud spacing will give a wrong PCD. Count the studs carefully.
• Mixing units – if you measure in inches, the output will be in inches. Convert to mm by multiplying by 25.4 if needed.
• Rounding too early – keep at least 3 decimal places in your sine calculation to avoid a 0.5 mm error in the final PCD.

Limitations of the Formula

This formula assumes the studs are evenly spaced on a perfect circle. In practice, hubs may have slight manufacturing tolerances. Also, some wheels use a bolt pattern that is not a regular polygon (e.g., asymmetric patterns), but those are rare on 2-wheel vehicles. For those, you need to measure all stud positions and fit a circle, which is beyond this simple formula.

How to Choose

When picking a bolt pattern calculator, the key is whether it uses the measurement you can actually take. Some calculators ask for the number of studs and the distance between two adjacent studs (like this one), while others ask for the distance between two non-adjacent studs. Make sure you know which measurement you have. Also check whether the output is in mm or inches – many aftermarket rims are spec’d in mm, but some older models use inches. Finally, verify your measurement with a second method if possible, such as measuring the hub diameter or using a bolt pattern gauge.

Frequently Asked Questions

What does PCD mean?

PCD stands for Pitch Circle Diameter. It’s the diameter of the circle that passes through the center of all the studs on a wheel hub. It’s the standard way to describe a bolt pattern.

Can I use this for 3-wheel vehicles?

Yes, the formula works for any number of studs, including 3. A 3-stud pattern is common on some scooters and older motorcycles. Just enter 3 as the number of studs.

What if I measure in inches instead of mm?

Just enter the spacing in inches and the calculator will give the PCD in inches. You can then convert to mm by multiplying by 25.4. The second output gives inches automatically if you enter mm.

Is the bolt pattern the same as the lug pattern?

Yes, they are the same thing. Bolt pattern, lug pattern, and PCD all refer to the arrangement of studs on a hub. The only difference is that some people include the number of studs in the description, like “4×100” meaning 4 studs on a 100 mm circle.

Why does my wheel have 5 studs but the spacing isn’t uniform?

Some hubs use a “dual pattern” with two sets of studs for different rims. In that case, measure each set separately. Also, if the wheel is bent or damaged, the spacing may be off. Otherwise, 5-stud patterns are always evenly spaced.

Can I use a bolt pattern gauge instead of measuring?

Yes, a bolt pattern gauge is a metal disc with holes at standard PCDs. You place it over the hub and find the hole that fits perfectly. It’s faster and less error-prone than measuring with calipers, but a caliper is more flexible for unusual patterns.

Final Thoughts

Knowing your wheel’s bolt pattern is essential for buying new rims, spacers, or adapters. This calculator gives you the PCD from a simple measurement you can take with basic tools. Always double-check your measurement and the resulting PCD against the manufacturer’s spec sheet if possible. A 1 mm error in PCD can cause wheel wobble or stud failure, so accuracy matters.

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in n | Number of studs | - | 4 | 3
in d | Adjacent stud spacing | mm | 82 | 10
out pcd | Bolt circle diameter | mm | d / (2 * sin(pi / n)) | 2
out pcd_in | Bolt circle diameter | in | pcd / 25.4 | 3