Wheel Fitment Guide: Understanding Offset, Bolt Patterns and Centre Bore
When buying new Wheels it is very important that you understand what fits your vehicle. They're are a variety of different things that determine the fitment of the wheel, some of which can be quite confusing. That's why we'll go through everything you need to know about Wheel Fitment in this guide.
What is Diameter?
The Diameter of a wheel is the width across from directly opposite parts of the rim.
It is essentially how "big" the wheel is.
Common passenger vehicle sizes range from 15" to 22", while some trucks and SUVs may use even larger diameters.
If a wheel is described using the numbers (18x8.5j), the diameter in this example would be 18".
Wheels come in a variety of different diameters and some may not be suitable for certain types of vehicle as once fitted, they may rub on the wheel arches.
What is Wheel Width?
The width of a wheel is simply the width or depth of the wheel from front (face) to back, the distance between the tyre mounting flanges.
Many people tend to put wider wheels on their vehicle as it is widely accepted that this will increase grip and stability as there is more tyre surface in contact with the road.
Using the same example of (18x8.5j), the width would be 8.5.
Knowing the width required for your vehicle is crucial for tyre fitment - too narrow and the tyre won't seat properly, but too wide and it may cause rubbing issues or improper tyre profile.
What is Offset?
The offset of a wheel is the distance in millimetres from the wheel's mounting surface (where it attaches to the hub) to the centreline of the wheel. It can be:
- Positive Offset - when the mounting surface is toward the front or outside face of the wheel. Most front-wheel-drive vehicles use positive offset wheels.
- Zero Offset - when the mounting surface is even with the centreline of the wheel.
- Negative Offset - when the mounting surface is toward the back or brake side of the wheel. This creates a "deep dish" appearance and pushes the wheel outward from the vehicle.
Offset is typically marked as "ET" followed by a number (e.g. ET45 means +45mm offset).
Choosing the correct offset is critical - improper offset can cause rubbing against suspension components, fender interference, and handling issues.
What is PCD or Bolt Pattern?
This measurement describes the diameter of the circle formed by the centres of the wheel lugs, and the number of lug holes.
Bolt patterns are expressed as
- Number of Lugs x Diameter in millimetres (e.g. 5x112mm)
Bolt patterns must match exactly - even slight variations can prevent proper mounting. While adapters exist, they can introduce additional complexity and potential failure points, so direct fitment is always preferred.
FAQs
How do I find the correct wheel specifications for my vehicle?
The most reliable sources for your vehicle's specifications are the owner's manual, the vehicle manufacturer's website, or the information sticker typically located on the driver's door jamb.
If you are unsure of the wheel specifications of your vehicle, do not hesitate to get in touch with us and we will be more than happy to help.
Can I install wheels with a different offset that what came on my vehicle?
Yes, but with caution.
Small variations (within 5-10mm) are often acceptable, but larger changes can affect handling, create clearance issues, and cause premature wear on suspension components.
Moving to a more positive offset pushes wheels inward, which may cause interference with suspension components.
Moving to a more negative offset pushes wheel outwards, potentially causing fender rubbing or extending beyond legal limits in some cases.
Our recommendation is to stay within 5mm of your factory offset for optimal performance and reliability.