Bolt Patterns

The bolt pattern is made up of the number of bolts and the diameter of the imaginary circle they create (BCD). The BCD can be expressed in inches or millimeters. Bolt patterns with an even number of bolts are measured from bolt center to bolt center. 5 lug bolt patterns are measured from the center of the upper bolt to the bottom of the lower bolts.

A bolt pattern is expressed as follows:


Where N = number of bolts and BCD = bolt center diameter.

For example, if you have a 5 lug wheel and your bolt center measures 114.3 millimeters then your bolt pattern is 5×114.3.

Parts of a Wheel

A wheel might look like a single object, but it is made up of several parts. To understand a wheel, you must understand the parts of a wheel. Let’s get acquainted with the most important wheel parts by starting at the center of the wheel.

The center bore is the opening that allows the wheel to fit on the axle. This is the part of the wheel that actually attaches the wheel to the vehicle and bears the weight of the vehicle. When you buy aftermarket wheels, you must ensure that the center bore is at least the size of the OEM wheel. This generally isn’t a problem as most manufacturers make wheels with a large center bore in order to fit as many vehicles as possible. When the center bore is larger, hubcentric rings are used to fill the gap. Center caps will cover the center bore with style.

Going out from the center bore is the center disc. This is the portion of the wheel into which the bolt holes are machined to create the bolt circle. This area is the point of contact to the axle seat, the lug bolts and the lateral surface of the rotor. Everything on the wheel connects in some manner to the disc.

The lug holes create the bolt circle with 4 or more openings. The diameter of the bolt circle is called the bolt circle diameter and abbreviated as BCD. The amount of holes and the diameter of the bolt circle is what defines the bolt pattern. Now that we’ve got the center covered, let’s move outward in our wheel anatomy.

The spokes connect the center disc to the outer ring of the wheel. The spokes give the wheel structural integrity and are one of the major elements of style in wheel design.

The outer lip is the portion of the wheel in front of the spokes. For the most part, the dish only comes into play when it is a large area. When the spokes are significantly distanced from the outer edge, the wheel is considered a deep dish wheel. This is done purely for aesthetic reasons. As the dish gets deeper, the face is more vulnerable to damage from impact.

Now, on the very outer portion of the wheel is the barrel. The barrel is what creates the structures necessary for mounting the tire. The barrel has many parts. The smallest inside diameter of the barrel is the drop center. If the drop center is close to the front face of the wheel, it is a front mount wheel. If the drop enter is close to the back face of the wheel it is a reverse mount wheel. The barrel edges are flared to create the flanges. The flanges keep the tire from slipping off. The outer facing flanges are part of the cosmetic face of the wheel.

Just inside the flanges are flat areas called the beads. This is where the edges of the tire sit onto the wheel. Mounting humps circle the barrel on both the car side and the cosmetic side of the wheel. These ridges separate the beads to keep the tire from slipping away from the edge of the wheel.

Now you know the parts of the wheel, let’s look at how the pieces are put together.

Wheel Sizes

Wheels come in a wide range of sizes. The low-end is anchored by 15 inch wheels; massive 26 inch wheels dominate the upper end and wheels of all sizes are available in-between. So, if your car or truck comes stock with 16 inch wheels why would you want another size? Two reasons: aesthetic appeal and performance.

Larger wheels just look better. They fill out the wheel well and that provides visual impact. It’s what we call pure wheel eye candy. Larger wheels carry tires with smaller sidewalls so you get better grip and performance. For off road vehicles, this translates to less roll and sway and more stability. The only downsides to upsizing are that larger wheels and tires weigh more so gas mileage suffers and acceleration from 0 to 60 is degraded. Car and Driver studies also determined that at the upper limits, the suspension is taxed and the ride can suffer.

Don’t forget, your vehicle was originally engineered to roll on stock size wheels. That means the speedometer, odometer, traction control, torque and gearing settings were based on the distance that the stock wheel and tire assembly would cover in one revolution. When you change the size of the wheel you must maintain the overall diameter of the wheel and tire assembly. So, as your wheels get larger, the standing size of the tire gets smaller.

A good rule of thumb is that for every increased inch of wheel diameter you must decrease an inch of standing height. This maintains the overall diameter. That means the wheel and tire will still cover the same amount of distance in one rotation but it will look so much better doing so.

A wheel size is expressed as follows:


Where D = diameter and W = width.

For example: 18×9 means the diameter of the wheel is 18 inches and the width is 9 inches.

Not sure upsizing really makes a difference? Seeing is believing.