How to Read Wheel Specs: 18x9.5 +38 5x100 Explained

Wheel specifications can look cryptic at first, but a size such as 18x9.5 +38 5x100 is simply a compact way of describing four important dimensions. Understanding those numbers makes it much easier to compare wheels, avoid incompatible bolt patterns and ask the right fitment questions before ordering.

What does 18x9.5 +38 5x100 mean?

Read the specification from left to right:

• 18 = wheel diameter in inches.
• 9.5 = nominal wheel width in inches, measured between the tyre bead seats.
• +38 = positive wheel offset in millimetres.
• 5x100 = five wheel studs or bolt holes arranged on a 100 mm pitch circle diameter.

18: wheel diameter

The first number is the nominal wheel diameter. An 18-inch wheel requires a tyre designed for an 18-inch rim. Diameter affects tyre sidewall height, brake clearance, ride quality, weight and the range of tyres available, but a larger diameter does not automatically mean better fitment.

When moving between 17- and 18-inch wheels, the tyre size normally changes as well so the overall rolling diameter remains appropriate for the vehicle.

9.5: wheel width

The second number is the nominal width between the bead seats. A 9.5-inch wheel is wider than an 8.5- or 9-inch wheel and therefore occupies more space on both the suspension side and the guard side.

Wheel width should always be considered together with offset. Two wheels can both be +38, for example, but the wider wheel will sit further inward and further outward. See our wheel offset guide and wheel width guide for a deeper explanation.

+38: wheel offset

Offset is the distance between the wheel mounting face and the wheel centreline. A positive number means the mounting face sits toward the outside face of the wheel.

Offset changes how far the wheel sits relative to the suspension, brakes and guards. Lowering the offset usually moves the wheel outward; increasing it usually moves the wheel inward. The effect must be considered with width, because changing width changes the centreline position and both clearances.

5x100: PCD or bolt pattern

PCD is not interchangeable just because the wheel has the same number of holes. A 5x100 wheel is not the same as 5x114.3, 5x112 or 5x120. The wheel and vehicle hub need the correct bolt pattern unless a properly engineered conversion system is being used.

For more detail, read Wheel PCD Explained: 5x100, 5x114.3, 5x112 & 5x120.

What the wheel size does not tell you

Even a complete-looking specification such as 18x9.5 +38 5x100 does not confirm fitment by itself. Other checks can include:

• centre bore and whether a hub-centric ring is required;
• spoke and barrel clearance around the brake caliper;
• tyre width, profile and approved rim-width range;
• inner clearance to struts, coilovers and suspension arms;
• outer clearance to the guard and bumper tabs;
• wheel nut or bolt thread pitch and seat type;
• vehicle load requirements and wheel specification;
• ride height, alignment and suspension modifications.

Our hub-centric ring guide and wheel-nut thread pitch guide cover two of the most commonly missed details.

Example: why the same offset can fit differently

Compare an 18x8.5 +38 wheel with an 18x9.5 +38 wheel. The second wheel is one inch wider overall. In simple geometric terms that additional inch is split roughly equally between the inner and outer sides, so the wider wheel occupies about 12.7 mm more space on each side before tyre shape and wheel design are considered.

This is why searching only by offset can be misleading. Width and offset should always be assessed together.

Before ordering wheels

Start with the vehicle's correct PCD, then confirm diameter, width, offset, centre bore, brake clearance and tyre choice. For vehicle-specific starting points, browse the HausofWheels Wheel Fitment Guides. To see current genuine wheel options, browse Genuine JDM & Performance Wheels.

Fitment information is a guide only. Vehicle specification, brakes, suspension, tyre choice and modifications can change clearance. Confirm the exact setup for your vehicle before ordering.