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Wheel fastener tightening

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Wheel fastener tightening

Care and attention to detail are key concerns whenever dealing with the installation of custom wheels, especially alloy wheels. Taking the time to do the job correctly will greatly reduce the potential for customer complaints.

Preparing for wheel installation

NOTE: Prior to installing any wheel (steel or alloy), verify the condition of the fastening system’s threads (nuts and studs or bolts and hub threads). All threads should be clean and free of dirt, grease, grit, etc. If burrs or flat spots are found, replace the offending fastener.

Before attempting to install the wheel to the vehicle hub, first verify that you have the correct size fastener, and check thread condition. Finger-install all fasteners. Each fastener should be able to be easily threaded into place without the use of a tool. If not, the thread size (diameter or thread pitch) may be incorrect, or thread damage may exist on either the stud and/or nut; or the wheel bolt and/or hub’s threaded hole. Resolve any fastener issues before attempting to install the wheel(s).

Once you’re satisfied with regard to the fasteners, if this is a first-time installation (new aftermarket wheels), it’s a good idea to first test-fit the wheels before mounting the tires to the wheels. Make sure that no obstructions exist on the hub face that would prevent the wheel from flush-mating to the hub (check for OE stud clips, etc.).

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Install the wheel to the vehicle hub, tightening at least three wheel fasteners. There’s no need to tighten to full torque value, just make sure the wheel fits flush against the hub face. Check for disc brake clearance and for clearance between the wheel rim and any steering/suspension components.

Also check hub fit. Some wheels are designed to be centered to the hub by means of the bolt holes (lug-centric), while others are designed to center to the hub via the hub center-to-wheelhub center hole (hub-centric).

If the wheel’s center hole is larger than the outer diameter of the hub’s centering housing, a hub-centric spacer may be needed to properly center the wheel to the hub.

There’s nothing wrong with using a hub-centric ring adapter. Some wheel makers may use the same center hole diameter to accommodate a variety of hub sizes. Using a centering ring allows a single center hole size to function on smaller hub diameters. Simply check this first to save time and aggravation. The rings, if needed, must be installed to the hub before the wheel is installed.

Wheel fastener torque

Many folks don’t realize it, but all threaded fasteners are intended to stretch slightly when fully tightened to specification.

In the case of wheel studs and nuts (or wheel bolts), this creates the correct preload required to properly secure the wheel to the hub.

If the wheel fasteners are under-tightened, they will eventually loosen, resulting in wheel damage or separation from the vehicle. If the fasteners are tightened beyond their design limit, the wheel stud or bolt can permanently stretch (fatiguing beyond its designed elastic range) or even break during installation.

While the use of an impact gun (or the use of an impact gun equipped with a torsional wrench) may be tempting in terms of saving time, let’s face it: the only way to ensure correct clamping loads is by taking the time to tighten wheel fasteners with the use of a quality and properly-calibrated torque wrench.

Never use an impact gun to tighten custom wheel fasteners. Not only will you not be able to accurately control the level of fastener tightness, but use of an impact tool can easily damage the fasteners or the adjacent wheel surface.

And when we’re dealing with attractive (and expensive) alloy wheels, such damage, even if only cosmetic, is simply unacceptable.

Use sockets that fit the wheel!

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Before attempting to engage a socket to the fasteners, first check to make sure that the socket is clean to prevent damaging the fastener finish. Also, verify that the socket of choice will comfortably fit into the wheel’s fastener hole (in those cases where the fastener sinks into a recess at the wheel’s bolt holes).

Using a socket that is too thick will cause the socket to jam and gall inside the recess, damaging the wheel finish (flaking off chrome, galling a powder coat finish, etc.). My preference is to set aside a dedicated set of thinwall sockets specifically for use on custom wheels. This provides a set of sockets that are kept clean, and that you know will not provide a too-tight fit into bolt hole recesses.

The use of a pneumatic (or electric) impact gun offers the potential of damaging the fastener’s exterior surfaces and/or the wheel’s fastener hole area, in both removal and installation procedures. In a nutshell: If you’re dealing with alloy wheels, leave the impact gun on the bench.

Here’s another tip: When tightening the wheel’s fasteners, don’t make the mistake of finger-tightening, then lowering the vehicle to the ground to continue tightening. Instead of fighting vehicle weight, it’s best to perform your complete tightening procedure while the tire is off of the ground. If the mating surfaces (wheel to hub) aren’t fully compacted together, placing the weight of the vehicle against the tire results in then overcoming the resistance of the sidewall deflection (due to vehicle weight), which could possibly result in inaccurate torquing.

INSTALLATION TIP: In order to prevent the wheel from sticking to the hub in the future (when an aluminum wheel is mated against a steel hub, this can result in electrolysis), it’s a good idea to apply a thin coating of an anti-seize paste to the hub face where the wheel makes contact.

A thin application of this compound will make it easy to remove the wheels in the future.

Re-torque

While opinions on re-torquing vary, the best suggestion is to re-torque all wheel fasteners after the first 50 to 100 miles, specifically after installing new wheels.

This is especially true of alloy wheels, since the initial fastener tightening may result in a slight compression of the wheel material (at the hub mating face).

If a bit of material compression occurs, this will directly result in a lower torque value at the fasteners, decreasing the clamping load.

The best approach is to initially tighten all wheel fasteners to specified value, drive the vehicle for 50 to 100 miles, and then re-torque the fasteners.

When re-torquing, raise the vehicle to lift the tires away from the ground (removing vehicle weight). Loosen all of the wheel’s fasteners (in a crisscross pattern), then re-tighten in the proper sequence to full specified torque value.

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Wheel fastener torque values

Always follow the vehicle maker or wheel maker torque specifications.

Just remember that tighter is not necessarily better.

While you should always adhere to the torque specifications listed by either the vehicle make or the wheel maker, the box below offers a broad guideline of torque values for common wheel fastener sizes.

Tightening sequence

Always tighten any wheel in the proper sequence pattern in order to evenly distribute the clamping load between the wheel and the hub.

Especially considering today’s comparatively lightweight hubs and brake rotors, if the wheel fasteners are tightened improperly (in terms of torque value and tightening pattern), the risk of creating a hub/rotor warpage increases, resulting in a brake pulsation. The goal in using the proper tightening pattern is to avoid concentrated areas of clamping force. You want to evenly distribute the clamping load across the hub surface.

Four-bolt hub

With the hub/wheel positioned so that one fastener is at the 12-o’clock position, tighten the 12-o’clock position first, followed by the 6 o’clock position, followed by the 3 o’clock position, followed by the 9 o’clock position.

Five-bolt hub

With the hub/wheel positioned with one fastener at 12 o’clock, tighten the 12 o’clock position first, followed by the 7 o’clock position, followed by the 2 o’clock position, followed by the 10 o’clock position, followed by the 5 o’clock position.

Basically, from the first fastener, move to a fastener that is furthest away from the first fastener. Then move to a fastener furthest away from that second fastener, etc. Always move to the fastener that is furthest away from the previous fastener.

Six-bolt hub

The same rule applies. After tightening the first fastener, move to a fastener that is furthest away from that first fastener, and so-on.

Always move to the fastener that is furthest away from the previously-tightened fastener.

An example of a six-bolt pattern would be: With the hub/wheel positioned to place one fastener at 12- o’clock, tighten the 12 o’clock position first, followed by the 6 o’clock position, followed by the 2 o’clock position, followed by the 7 o’clock position, followed by the 5 o’clock position, followed by the 10 o’clock position.

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NOTE: For ideal clamping results, it’s best not to fully tighten the fasteners in one step. Instead, tighten in at least two steps. For instance, if the specified torque value is 100 ft.-lb., tighten all fasteners (in the proper sequence pattern) to an initial value of 25 ft.-lb. Then perform a second tightening to full value (using 100 ft.-lb. as our example). By tightening in multiple steps, you greatly reduce the chance of initiating excessive clamping force in isolated areas. Taking this extra care is but another way of increasing your chances of achieving an optimum wheel-to-hub clamping load.

Fastener dimensions

Sizing any threaded fastener involves several dimensions, including diameter, thread pitch and length. Following are the basics.

Thread diameter refers to the diameter of the threaded section of the fastener (outer diameter of a bolt shank or stud).

For example, if you measure the thread diameter of a 1/2-inch stud using a dial caliper, the diameter measured at the thread peaks will measure almost 1/2 inch (usually the exact measurement will be 0.005 - 0.008 inch or so less than exactly 1/2 inch).

Wheel fasteners exist in both inch and metric formats. Common inch-format wheel fasteners include 7/16 inch, 1/2 inch and 9/16 inch. Common metric-format wheel fasteners include 10mm, 12mm and 14mm.

Thread pitch refers to the number of threads or spacing between the threads.

In the inch format, the pitch refers to the number of threads found within a one-inch length of threaded area. For example, a 1/2 inch x 20 fastener is 1/2 inch in diameter, with 20 threads per inch of threaded area length.

A pitch of 20 is commonly referred to as a “fine” thread (as compared to a 1/2 inch x 13 size, which would feature only 13 threads per inch, commonly called a “coarse” thread.

The terms coarse or fine are relative terms, depending on the thread diameter. For instance, a 1/4-inch diameter bolt with a 20 thread pitch is considered coarse, while a 28 thread pitch is considered fine. On a larger diameter bolt, such as a 1/2 inch bolt, 20 pitch is fine and 13 pitch is coarse.

In the metric format, thread pitch refers to the distance between threads. For example, a thread pitch of 1.25 indicates that the distance between two adjacent threads is 1.25mm. If the thread pitch is 1.50, the distance between threads is 1.5mm. In metric format, the higher the number, the more “coarse” the thread pitch.

For example, a 1.0 pitch is “very fine,” a 1.25 pitch is “medium fine,” a 1.5 pitch is “medium” and a 1.75 pitch is “coarse.”

In the inch format, the higher the pitch number, the finer the threads.

In the metric format, the lower the number, the finer the threads.

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While it may seem confusing at first, once you understand the measuring approach, it will be easy to identify thread sizes.

With regard to wheel fasteners, the threads are always “fine.” As compared to coarse threads, this provides increased bolt strength and potential clamping load. If a wheel fastener is 7/16-inch diameter, the thread pitch will be 20. If 1/2-inch diameter, thread pitch will be 20. If 9/16-inch diameter, thread pitch will be 18. Metric wheel fasteners will either feature a 1.25 or 1.5 thread pitch, regardless of thread diameter.

Thread engagement length is critical. At the minimum, thread engagement length must be equal to or greater than the diameter of the fastener. In other words, if the stud is 1/2-inch in diameter, the nut must engage onto the stud by at least 1/2 inch. If not, either a longer stud or longer nut must be used (if a longer nut is needed, the nut must protrude further through the wheel hole to meet the stud). Use of longer nuts is possible when the nut features an extended shank that offers greater thread length. This will vary depending on nut style. If this isn’t feasible, a longer stud must be used.

When using wheel bolts or capped nuts, care must be taken to avoid bottoming the bolt or nut. For example, if the stud offers one inch of exposed length for nut engagement, but the threaded hole in the nut is only 3/4 inch deep, the nut will bottom-out on the stud and will not clamp the wheel against the hub.

Pay attention to length, instead of blindly screwing on whatever nuts are handy at the time.

HANDBOOK Q&A: What are the various fastener drive styles?

Common wheel fastener drive styles will involve either a male or female hex or a spline drive that features a series of grooves or splines.

A spline drive style requires a special splined socket, while male hex head nuts or bolts require a six-point socket. Small-diameter spline-drive fasteners are commonly found on many “tuner” style wheels in order to accommodate small hub areas. By the same token, a female-hex type nut or bolt allows the use of smaller outside diameter fasteners where space is at a premium. These require the use of a hex bit (in slang terms, this is often called an “allen” wrench, a term that isn’t always correct, since the term “allen” actually denotes a specific tool brand).

In short, if you plan to service today’s custom wheels, it’s important to realize that you’ll need a broader array of tools beyond a basic selection of female six-point socket wrenches.

Another point worth mentioning relates to socket wall thickness. In many cases, the clearance between the fastener and the wheel’s bolt hole entry cavity is very tight, requiring the use of thin-wall sockets to avoid scarring the wheel finish. This is something that many shops tend to ignore, until it’s time to install or remove the wheel. Our suggestion would be to stock a small inventory of thin-wall 1/2-inch-drive deepwell sockets (for servicing hex-headed wheel nuts or bolts), that are dedicated only to custom wheel service. Another benefit to this approach, as long as you don’t use those sockets for routine repair jobs, is that the sockets will remain “healthy” — clean, with minimal wear and burrs that could damage chrome fasteners.

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HANDBOOK Q&A: What are the various fastener seat styles?

The “seat” refers to the actual contact area between the fastener’s head and the wheel.

It’s critical to understand that the seat style of the fastener must match the seat style featured on the wheel. If the wrong seat style is used, the wheel simply will not be fastened to the hub correctly. If the seat style of the fastener does not match that of the wheel, you’ll likely damage the wheel finish, and more importantly, the wheel will eventually loosen and wobble as it moves in relation to the hub.

In short order, any play between the wheel and the fasteners will ruin the wheel’s fasteners holes, resulting in either severe wheel damage or complete loss of the tire/wheel assembly.

The seat styles most commonly found include radius, conical, and flat (“mag”). These terms refer to the shape of the seat (where the fastener contacts the entry of the fastener hole in the wheel).

Radius seats are also called “ball” seats, since the base of the nut (or base of the head on a wheel bolt) features a ball shape, which mates into a wheel’s female radiused ball relief at the wheel’s mounting hole.

Conical seats are often referred to as “tapered” seats. This style features an angled seat wall (a “cone” shape). The fastener will feature a male cone seat, and the wheel will feature a female cone entry hole. The most common angle of taper is 60 degrees.

Mag wheel nuts feature a flat contact patch at the wheel (the nut usually features a thick flat washer). A mag-style nut may also feature a smooth outer-walled shank that served to help center the wheel on a lug centric design, as the shank enters the wheel’s bolt hole and serves as a guide pin to center the wheel’s hole over the wheel stud. When using a capped nut (where the female threaded hole does not pass all the way through the nut), it’s important to pay attention to thread engagement length. At the very least, the nut must engage onto the stud at a depth that is equal to the stud diameter. For example, if the stud diameter is 12mm, the nut must thread onto the stud by at least 12mm of depth. Also, make sure that the stud does not bottom-out inside the nut. If the stud bottoms out, it will be impossible to achieve full clamping load.

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