Tech Stuff

Wheel fasteners: Understanding the nuts and bolts of wheel clamping

 

If the vehicle is on a frame lift, and a helper is able to lock the brakes, the wheel fasteners can be final torqued while on the lift. Otherwise, lower the vehicle to the ground until the tires just begin to load (enough to prevent rotation while torquing). If the vehicle is on the ground with its full weight on the tires, you may be fighting a slight lateral load while final tightening. This is perhaps an arguable point, but final tightening before the suspension is fully loaded helps to obtain a more precise centering of the wheel fastener seats.
<p>If the vehicle is on a frame lift, and a helper is able to lock the brakes, the wheel fasteners can be final torqued while on the lift. Otherwise, lower the vehicle to the ground until the tires just begin to load (enough to prevent rotation while torquing). If the vehicle is on the ground with its full weight on the tires, you may be fighting a slight lateral load while final tightening. This is perhaps an arguable point, but final tightening before the suspension is fully loaded helps to obtain a more precise centering of the wheel fastener seats.</p>

The threaded fasteners that secure the wheels to the chassis are perhaps the most critical components on any vehicle, yet they’re often the most overlooked and under-appreciated. Improperly sized threads or seat styles or improperly installed wheel fasteners can result in loss of a wheel and tire package (wheel separation from the vehicle) during vehicle operation. With that in mind, we need to pay more attention to these vital fasteners.

While it may initially seem simplistic to devote an entire article to this subject, its importance and the need to educate beginning or apprentice technicians cannot be overemphasized.

Here, we’ll provide a basic overview of the often overlooked threaded wheel fastener — how to identify it and how to handle it. This includes information dealing with fastener thread size, seat styles and torque values.

Our goal is to provide clear and accurate explanations of various wheel fastening systems that will help to train new technicians (as well as imparting this knowledge to your customers).

NOTE: The common method of attaching a wheel to a hub involves a group of individual threaded wheel fasteners (wheel nuts or wheel bolts), involving a pattern of four, five, six or eight fasteners per wheel. Another type of wheel clamping system involves attaching the wheel to the hub with a single spindle nut. This is most commonly referred to as a knock-off or pin-drive system. Since it’s rare that your shop will encounter a pin-drive system, we’ll focus on multiple threaded fastener designs.

Shown here are four examples of wheel fasteners. From left: spline-drive nut with a conical (tapered) seat; hex drive nut with conical seat and shank extension to accommodate thick alloy wheels; radiused (ball type) hex drive nut; and a wheel bolt that features a ball type radiused seat.
<p>Shown here are four examples of wheel fasteners. From left: spline-drive nut with a conical (tapered) seat; hex drive nut with conical seat and shank extension to accommodate thick alloy wheels; radiused (ball type) hex drive nut; and a wheel bolt that features a ball type radiused seat.</p>

Clarifying misunderstandings

While it’s difficult to break with the use of traditional terms (i.e. “lug nuts”), the term “wheel fasteners” is more appropriate.

Remember that not all automotive wheels are secured with studs and nuts. For example, many German vehicles use wheel bolts instead, which engage into threaded holes in the hub face. So, constantly calling all wheel fasteners “lug nuts” simply isn’t accurate.

The basic factors to consider when selecting wheel fasteners includes:

•  Thread diameter

•  Thread pitch

•  Thread length/thread engagement

•  Fastener seat style

•  Installed torque (clamping load)

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