Alloy Wheel Size Guide: How to Choose the Perfect Fit for Your Car

Wheelbase alloys are a perfect addition to your car, giving it a brand-new look with minimal effort. However, when choosing your alloys, there are several things you must consider when it comes to sizing them up. Whether you are buying alloys for the first time or simply looking for some clarification, G-Force Styling is here to answer your questions.

This guide is designed to clear up any grey areas on all things alloy sizes, from general information to specific processes you should complete before purchasing. Once you’re up to speed with our latest tips, you can browse our vast range of alloys to determine your favourite colour or necessary size, with 24” alloy wheels being the largest of our stock.

Alloys: The need-to-know

Aluminium is the dominant material on alloy wheels and is much more common than the other main wheel type, steel. While alloys are typically fitted on most vehicles directly by the manufacturer, steel wheels tend to cater to lower trim or base models.

An obvious perk of alloy wheels is their striking visuals, with a change of wheel being an easy way to add a strikingly rich aesthetic to your vehicle. There are also various practical elements of alloy wheels:

Good grip

Embedding alloys on your vehicle can increase its surface area, causing it to have more direct contact with the road. Not only does this help to maintain grip naturally, but it enhances the steering response of your vehicle and equalises the amount of pressure on your wheels when driving.

Prolongs brake effectiveness

Older wheels tend to react to heat less effectively than alloys on particularly long drives, which can encourage brake failure. Alternatively, alloys manage heat more seamlessly, distributing the heat from your brakes to keep them working at their best for longer.

General performance

With a reduction in unsprung weight thanks to your alloys, your driving experience will see enhanced acceleration, clear-cut steering and a lower fuel consumption rate.

Key terms

Away from the practical perks of alloys, there are some key terms to familiarise yourself with:

• Wheel rim: The wheel's outer edge which holds the tyre in place. The rim is purposefully designed in a U-shape to support the part of the tyre that directly connects with the rim, also known as the tyre bead. This design causes the centre of the wheel to sit further back into the tyre for protection.

• Alloy Wheel Offset: Wheel offset relates to how your wheels are positioned in your wheel wells. It is crucial that your wheel offset is accurate, as this ensures the efficient function of your vehicle's brakes, suspension and particular body parts. There are three categories of offset:

• Zero offset is where the mounting surface of your wheel is in line with the centreline, the centre point of your wheel, if you were to vertically half it.

• Positive offset causes the wheel's mounting surface to be set on the outer side of the wheel, facing outwardly towards the street. Positive offset is the most common type of offset amongst manufacturers.

• Negative offset is the opposite of positive, where the wheel’s mounting surface sits back towards the inside edge of the wheel, creating a ‘dished’ effect, often seen in trucks.

• Backspacing: The amount of space between the backside of the wheel and the wheel’s mounting surface.

• Bolt Patterns: The measuring technique to determine the number of lugs on your wheel and the distance between them, also referred to as the Pitch Circle Diametre (PCD) or lug pattern. A lug is a fastener that holds your wheel to your vehicle’s axle.

• Wheel centre bore: The hole positioned at the back of the wheel’s centre to accommodate the spigot, which is placed between the wheel rim and the car wheel hub. The wheel centre bore is measured in milimetres. 

With the background information established, it is time to measure your alloy wheel size using our simple step-by-step guidance.

Generally, you can measure what sized alloy you need with the following format:

Wheel diameter x Wheel width

20 x 8.5J

While the wheel diameter and width are measured in inches, the J refers to the bead profile of the wheel. However, further considerations must be taken to ensure you choose the best alloys for your vehicle.

How to measure alloy wheel width

The width of your alloy wheel refers to the distance between your wheel's outer and inner lips. Each wheel contains a compatible rim width range, which can differ by a couple of inches. These various measurements make it essential for establishing accuracy.

How to measure alloy wheel PCD

The wheel pitch circle diameter is condensed to PCD for ease and is measured in millimetres. The measurements are determined by the number of bolts that hold your alloy wheel in place and where they are positioned. 

• To measure your alloy wheel PCD, gauge the number of bolt holes in your wheel. These holes will be positioned in a circular shape called the bolt circle.

• Whether your wheel requires 4 or 6 bolts, measure the diameter of the circle they create in reference to the centre of each hole.

How to identify bolt patterns

Wheels containing 4 bolts would present as a diamond or square shape. Alternatively, this shape will differ and appear more circular when more bolts are required, making the measuring process easier. As mentioned, you should measure the distance between each hole, specifically up to the centre of each. If your wheel contains an odd number of bolts, you may need specialist tools to achieve accuracy.

The most common format for bolt holes and PCD is:

Number of Bolt Holes x PCD Diametre (mm)

4 x 100

How to measure alloy wheel offset

The wheel offset refers to the distance from the hub-mounting surface to the centreline of your wheel. Your measurement may be positive or negative, depending on the positioning of the hub mount.

The offset number is formatted as ET40, which equates to an offset of 40mm.

While lower offset numbers indicate your wheel protrudes on the outer side of your vehicle, higher numbers relate to the opposite. If the offset is too low, your wheel will sit unnecessarily further away from the car, while higher measurements will negatively affect the bodywork or suspension.

Similar to measuring the width of your alloy wheel, accuracy is required as there is no fixed size for a vehicle wheel offset. While 2% is the general difference accepted by manufacturers, you should consider wheel offset measurements on a basis that is relevant to every individual vehicle.

Find the best alloys for you at G-Force Styling

At G-Force Styling, we are committed to providing an eclectic range of top-quality wheel alloys, so we stock some of the best brands, including AEZ, Autec and Fox.

Purchase the best wheel alloys for your vehicle today and get a Free Fitting Kit with Every Alloy Purchase!