In our ever-changing performance industry, we must always be aware of what our retail customers need and demand from us. Technical knowledge – the ability to quickly and accurately help them make the best and safest wheel and tire choices – is paramount.

Time was that custom wheel selection and fitment was relatively simple. Not today, with all different vehicle configurations, tire sizes, and wheel types and styles to deal with. Not to mention customer desires, constantly changing wheel designs and practical issues like clearances.

To become a performance tire/custom wheel “expert” your customers will appreciate, there is a lot to know and understand. And the best place to start is at the beginning: the basics of wheel construction and terminology.

Wheels Inside & Out

Ever wonder what someone is talking about when they mention bolt pattern, offset or backside setting? Well, you’re not alone. Most people in the tire/wheel industry don’t fully understand their meaning or their relationships to each other and the vehicle.
In measuring a wheel you need to understand all aspects of what makes up the individual parts of the wheel. Our focus begins with terminology and measurements (Diagram 1).
Wheel Diameter: Measured in inches or millimeters.

Wheel Width: Measured on the inside (not the outside) of the inner and outer rim flange.
Offset: The distance in millimeters that the inside surface of the mounting pad is from the centerline of the wheel. If the mounting pad is forward (toward the street), it is positive offset. If the pad is toward the rear, it is negative offset.

Backside Setting (Rear Spacing): The distance from the rear rim flange to the mounting pad.

Caliper Clearance (X-factor): The amount of clearance built into the wheel to allow for the vehicle’s brake rotor and caliper assembly.

Mounting Pad: The surface of the wheel that touches the vehicle’s hub.

Center Bore: The opening through the center of the wheel.

Drop Center : The inside of the wheel into which the bead will be placed to mount the tire. May also be reversed and have to be mounted from the back.

Safety Hump: The small rise that helps hold the tire in place.

Wheel Weight Contour (Inboard/Outboard Flange): Different OE/aftermarket manufacturers have different shapes to their flange, thus requiring weights specifically designed for those wheels.

Bolt Circle: On a 5-lug application, measure from the center of one stud or bolt hole to the outer edge of the stud or bolt hole across the center. For 4-,6-,8- or 10-lug applications, measure from the center of one bolt hole to the center of the bolt hole directly across the center.

Measuring Backside Setting: See Diagram 2. Measure backside setting by placing the wheel face down. Use a clean mat to protect the face. Next, place a straight edge across the rear rim flange and let it overhang the wheel. Now, place a ruler perpendicular to the straight edge down to the mounting pad. This measurement – in inches – is the backside setting.

The backside setting has a relationship to offset. The following formula will help you to understand this better. Offset is relative to the width and backside setting of the wheel. For example, with the 6-inch-wide wheel in Diagram 2, take this 6-inch width and add 1-inch to it. The front and rear flange must be used in this calculation, which are roughly 1/2-inch each.

(Width +1-inch) / 2 = Centerline (3.5 inches)

The backside setting was 3 inches. Therefore, the distance from the mounting pad face to the centerline is .5 inches. Multiply this by 25.4 to determine the offset in millimeters (24.5 millimeters equals one inch), which, in this example, is 12.7mm. It is negative because the mounting pad is toward the rear of the wheel.

Other Key Terms

Terms that indicate the relationship of the mounting pad to the centerline of the wheel are illustrated in Diagram 2.

Reverse Offset (REV): Mounting pad is near the rear of the wheel.

Standard Offset (STD): Mounting pad is at or near the centerline.

Medium Offset (MED): Mounting pad is between the centerline and street side of the wheel.

High Positive Offset (HPO): Mounting pad is toward the street.

Fastener Facts

Now that you have a solid terminology foundation from which to build on, let’s take a look at mounting hardware – wheel fasteners, as they are called.

This may seem like a trivial matter, but the fact is that for all of the work that you do in your shop, a fifty-cent piece of metal can cause a lot of misery and liability.

First, the more common wheel fasteners or lug nuts used in the aftermarket are the acorn or conical seat lugs which typically have a 60 degree angle (Diagram 3). Beware, though, because some manufacturers use a 63 degree angle on some tuner-style wheels.

Acorn lug nuts come in two distinct designs. One has a 13/16-inch hex and is straight from top to bottom, while the other has a 3/4-inch hex with a bulge at the base before the angle begins.
Make sure that when you replace lug nuts that the customer’s own lug wrench will fit properly. Many times, this is overlooked, and will create an upset customer if he/she can’t change a flat tire. Also, if you sell custom wheels that require a thin wall socket to reach the lugs, make sure that it’s compatible with the customer’s lug wrench, as well. If not, you’ll have to make sure he/she can acquire the right wrench.

In the last few years, the automotive industry has seen more changes in bolt circles and thread pitches than in the last 20 years combined. One major problem that has cropped up for dealers is the increased length of lug studs. This means that a standard length lug nut will bottom out before fully applying the proper seat pressure against the wheel.

The problem is that you may not notice. The wheel may look tight, but it is actually ready to come off as soon as the customer drives away. The solution here is to use duplex length lug nuts. These are available in both hex sizes and are approximately 1/2-inch longer than standard. Typically, bulge head lug nuts are needed for aluminum wheels with deeper lug holes, but can be used on steel wheels.
Next, we have the mag shank lug nuts. These lug nuts are available in multiple lengths depending on the application. Each requires a washer, either separate or built-on, to apply the proper seat pressure and keep the lug nut from scarring the face of the wheel. The most common are the short shank, standard shank and extended shank (Diagram 4). There are other lengths, but these are the most commonly seen.

Mag lug nuts for aftermarket wheels are typically designed for vehicles that were built 20-30 years ago. This means that most new thread pitches are not available in a mag shank lug.
Keep in mind, these will not fit old style wheels that accept three different bolt patterns. Certain wheels, like the Cragar S/S, were modified – the lug hole was enlarged – to accept the 14mm lug. This means that a Cragar S/S that came off of a pre-1988 GM 1/2-ton 2WD will not work on a 1988-98 truck.

Watch the Washers

While we’re on the subject of mag lugs, let’s talk about the different washers needed for some common applications (Diagram 5). Washers are either centered or offset, depending on the application, and some are thick and others thinner. Offset washers are used on vehicles with either a 5×4.5 or 5×5 bolt circle. Center-punched washers are used on vehicles with a 5×4.75 bolt circle.

Next, let’s look at the larger duplex and dualie lugs. Make sure that when you order lugs for 3/4- and 1-ton trucks that you have the proper length lug nut. For example, Ford F250 and F350 trucks from the mid-1980s to late-1990s require XXL length lug nuts. Also, some dualie wheels require special lug nuts, such as a 90-degree acorn or a washer either built-on or separate.

Next, we have the ET mag lug nut. This is an acorn lug nut with a small shank on the end. These lug nuts are of great use to help center a wheel onto the lug studs. Aftermarket wheels are not typically hub centric like the factory wheels. On occasion a vibration will occur in a front-wheel drive vehicle, and using these types of lugs and a centric ring will help eliminate the vibration (Diagram 6).

Our last major type of lug nut is one of the newest (Diagram 7) on the market. The socket lug or “tuner” lug is a very narrow lug nut that will just barely fit into the lug hole of a tuner-style wheel. They are available in colors and in chrome. In some cases, these lug nuts are installed with a key that engages the lug nut through the center instead of the outside of the lug nut. Others have splines on the outside that require a special wrench adaptor. In either case, make sure your customer gets (or you can give one to them for free) the proper key or adaptor in case of a on-road emergency.

It is recommended that you torque these types of lug nuts by hand, as too much abuse from an impact wrench can damage the key or adaptor or, in some cases, snapping the fastener off altogether. A word of caution regarding socket lugs: Make sure that the lug studs on the vehicle aren’t too long or the key will be pushed out of the head of the socket lug, making it is almost impossible to torque the lugs properly.

Most important, make sure that all lug nuts are hand torqued to the proper specification. Too loose has obvious consequences as a wheel-off situation could occur. Too tight could crack the alloy wheel right at the hub, creating a potential liability nightmare.

Types & Construction

Okay, we’ve discussed wheel terminology and the importance of wheel fasteners. Let’s look at wheel construction, types of finishes and the pros and cons to each.

Understanding the nuances of each will allow you to guide your customer to the right kind of wheel to fit their specific needs and application.

First, wheel construction. Almost everyone is familiar with steel wheels – an inner face welded to an outer rim. But what about aluminum or alloy wheels? How do they differ and what’s their purpose? Read on and you’ll be one step closer to becoming the highly trained professional that customers demand.

One-piece cast wheels are just that. They are formed from molten metal injected into a segmented mold. Once released from mold, the wheel goes through final machining and cleaning processes.
Cast one-piece wheels are typically the heaviest of the three wheel types, although advances in mold design over the years have significantly reduced the weight. A big plus to this wheel is the strength of the outer rim flanges – where the tire beads meet the wheel.

Another plus is that these wheels can withstand a great deal of punishment, making them a good choice for typical off-road applications. If they’re damaged, repairing them is usually possible. Also, the design flexibility is only limited to imagination and mold constraints, giving consumers lots of choice.

Another one-piece option is the forged wheel, which is milled out of a solid chunk of aluminum (or alloy). While they can painted, polished or chrome-plated, one-piece forged wheels are usually offered in only one offset per size, so you don’t have the flexibility to adjust the backside setting.
Two-piece wheels consist of a center that is welded to an outer rim. The centers can be cast or machined out of solid aluminum or alloy (forged or billet).

The outer rim, however, is usually “spun” from flat metal and then welded at a joining seam. There are some instances where a cast outer rim is used, especially to create the “waterfall” or soft lip that doesn’t allow for weights to be hammered on the outside flange.

Centers on two-piece wheels are usually painted or polished, and the outer rims are usually polished. Popular deep lip wheels are two-piece. Rarely is a two-piece wheel chrome plated, except in the case of a composite wheel.

A composite wheel is created when an aluminum center is welded to an outer steel rim. The center is chrome plated separate from the outer rim, then pressed together and welded. Typically, a weight savings is realized with a two-piece wheel because the outer rim is lighter than the comparable part of a one-piece wheel.

One major benefit to this type of wheel is the availability of widths and backside settings. And this type of wheel can be custom-built to exact measurements allowing you to maximize the available fender well space by choosing the widest wheel and biggest tire combination to fit the vehicle.
Three-piece wheels are designed so that the center, formed by one of the previously mentioned processes, is bolted to two sections of outer rim halves. This lets the manufacturer change the width of the front and back halves of the wheel to create the desired backside setting.

Three-piece wheels are extremely expensive, but they offer the greatest sizing flexibility and are generally light weight. Three-piece units can also be chrome-plated by having the center and outer rim half plated, then assembled with bolts.

Multiple Finishes

Next, let’s look at wheel finishes and the pros and cons of each. First are painted wheels, which feature a powdercoat paint that is electrostatically applied. This means that they hang on a hook that draws a negative current through the wheel while positively charged paint is sprayed on the wheel. A clearcoat is then applied to further protect the finish. A baking process will cure the coating to a hard durable finish.

• Pro: These wheels can be refinished if damaged and only require soap and water to clean. Never clean a hot wheel or clean one in direct sunlight; some cleaners react to heat and can cause damage to the clearcoat.

• Con: The finish doesn’t have the high luster of a polished or chrome wheel.

Next is the polished wheel. Here, the bare metal is color buffed on a polishing wheel using a polishing rouge, which is available in different grits. Once the wheel is cut with a heavy grit, it is buffed with a mild grit polish to smooth the surface. Advances in technology have created new processes that allow the wheel to be polished on a lathe with special diamond bits.

• Pro: These wheels can be repaired if scraped or bent. They have a reflective finish that looks good and is a modest increase in price over painted wheels.

• Con: This wheel will become dull over time and have to be polished to bring back the luster of the finish. Regular waxing will prolong its shine.

Last is the chrome wheel. It’s a common misconception is that these wheels are “dipped” as though dunking them in a paint barrel. Although there are new “chrome” paint processes that have been introduced in the last few years, the most prevalent process is electroplate.

Part science and part luck, here is the process so that you can explain why a chrome wheel is more expensive than the rest. Wheels are placed on a rack that draws a negative current through the wheel. After thorough cleaning, the wheel is placed in a positively charged copper solution, which causes particles of copper to form on the surface of the wheel.

Once removed from the copper bath, the wheel is buffed to a high shine. Then it goes into a nickel-plating process, which add layers of durable nickel to the wheel. In some cases a micropourus nickel is added to further enhance the durability of the plating. Finally, chrome is applied to seal the nickel. So what you see isn’t so much chrome as it is the nickel, but common nomenclature is to call it a chrome wheel.

• Pro: Extremely reflective finishes that is the most desirable of luxury wheels. They generate excitement – especially in a showroom – that attracts customers. Wash with soap and water and the finish will remain “brand new.”

• Con: If the wheel is curbed or scratched, generally it cannot be repaired. A heavy salt environment can lead to corrosion that will attack the finish (usually from the inside of the tire) and cause peeling. Wax is a good preventative measure.

I hope that this will help you to guide your customer to the right wheel to fit their desires and budget. Remember, if you don’t sell yourself as a performance professional, your competition sure won’t do it for you!

You’re on the front line in the battle to win the confidence of performance consumers. With the right knowledge, you will win.