Wheel Studs and Lug Nuts, Hooray! Part 1

Wayne Scraba

12 Dec 2017

Click Here to Begin Slideshow Wheel studs and lug nuts are pieces of hardware many people simply take for granted. If a wheel doesn't fall off in the water box or on the launch, then you've found bliss. Unfortunately, these pieces fall into the "who cares" domain of the racecar. Why worry about parts if they work? There are plenty of reasons to give these components some extra thought, not the least of which is safety. Not only are these parts much more important than you might think, picking the proper rear wheel studs, nuts and washers might not be as easy as you think either. Here's why: Consider the actual wheel bolt circle on the axle (it influences the loads placed upon the wheel stud). It's common knowledge among axle manufacturers that the largest possible bolt circle that "fits" the application should be used. For example, when buying new brakes along with new axles, it's relatively easy to specify a larger-than-stock wheel bolt pattern. It's also possible to re-drill a set of brake drums so that axles with a larger-than-stock bolt pattern can be used. Bolt Patterns Matter… Why is the wheel bolt pattern so important? Simple. When the pattern size is increased, the unit load per stud is reduced slightly. The larger the bolt pattern diameter, the lower the force imposed upon the wheel stud. The most common pattern by far is the 5 on 4-3/4" size (which is usually associated with mid-size GM products). Of course, this doesn't apply to alcohol and fuel cars - they typically use larger patterns (with the result being less unit load per stud). Bigger Is Better… The stock GM wheel stud size of 7/16-inch (or equivalent metric size) is simply inadequate on the drive axle for any vehicle destined for competition (even mild competition) or other high performance use. All race applications should have their drive axle studs replaced with a minimum 1/2-inch fastener. For example, Mark Williams does not offer axles in the 7/16-inch stud format and as a result, supplies all axles drilled and tapped to accept 1/2-inch or larger studs. Proper replacement studs are fashioned from high strength materials (often chrome moly steel) and are threaded all the way to the head. Because of this, the stud can be fully engaged in the backside of the axle. As mentioned above, 1/2-inch fasteners are the bare minimum starting point for wheel studs. Remember that the stud is the element that actually transfers the load to the wheel, and the wheel and tire are what transfer the load to the drag strip. And some of these loads at the axle might be much larger than you think. Look at the basic math (and I mean basic - there's nothing here that takes the tire "hook," track conditions or overall tire dimensions into consideration): Engine Torque x Torque Converter Multiplication x Transmission 1st Gear Ratio x Rear Axle Ratio = Load. Using a typical small block powered Stock Eliminator car, the loads can exceed 10,000 foot-pounds of torque at the axles. Arguably, there are two axles and ten studs over which to distribute this load, but it's still a bunch. Because of this, the vast majority of serious drag cars can benefit from the use of "drive studs." These are huge studs that measure up to a full 11/16-inch in diameter (on the drive shoulder). Designed to fit the holes in aluminum race wheels (i.e.: Centerline, Cragar, Weld, Bogart, etc.), the studs make use of an equally huge 5/8-18-inch axle thread (the portion of the stud which screws into the axle). Consider these components overkill if you like, but if bent or broken axle studs are plaguing your car, you need them. A good example of a quality drive stud is the MW piece shown in the following photo. These studs have 11/16-inch diameter shoulders for use with racing wheels. The drive stud is threaded into a 5/8-18-inch thread in the axle flange and secured with a jam nut. Wheels are held on with an open-end flanged lug nut with an aluminum washer. The drive studs incorporate a smooth shoulder (see the photos) that physically drives the wheel. In comparison, a street lug nut for aftermarket wheels has a built-in shoulder that drives the wheel. These street-oriented lug nuts are designed for use with small diameter studs (1/2-inch being the largest). In simple terms, the street models use much smaller diameter studs and the actual lug nut serves to drive the wheel. Obviously, this isn't the most efficient way to handle large torque loads. Next issue, we’ll dig deeper into drive studs. We’ll show you how to figure out the length of the stud along with the thickness of the respective washers you’ll need. Watch for it.

Wheel Studs and Lug Nuts, Hooray! Part 1 — Click Here to Begin Slideshow Wheel studs and lug nuts are pieces of hardware many people simply take for granted. If a wheel doesn't fall off in the water box or on the launch, then you've found bliss. Unfortunately, these pieces fall into the "who cares" domain of the racecar. Why worry about parts if they work? There are plenty of reasons to give these components some extra thought, not the least of which is safety. Not only are these parts much more important than you might think, picking the proper rear wheel studs, nuts and washers might not be as easy as you think either. Here's why: Consider the actual wheel bolt circle on the axle (it influences the loads placed upon the wheel stud). It's common knowledge among axle manufacturers that the largest possible bolt circle that "fits" the application should be used. For example, when buying new brakes along with new axles, it's relatively easy to specify a larger-than-stock wheel bolt pattern. It's also possible to re-drill a set of brake drums so that axles with a larger-than-stock bolt pattern can be used. Bolt Patterns Matter… Why is the wheel bolt pattern so important? Simple. When the pattern size is increased, the unit load per stud is reduced slightly. The larger the bolt pattern diameter, the lower the force imposed upon the wheel stud. The most common pattern by far is the 5 on 4-3/4" size (which is usually associated with mid-size GM products). Of course, this doesn't apply to alcohol and fuel cars - they typically use larger patterns (with the result being less unit load per stud). Bigger Is Better… The stock GM wheel stud size of 7/16-inch (or equivalent metric size) is simply inadequate on the drive axle for any vehicle destined for competition (even mild competition) or other high performance use. All race applications should have their drive axle studs replaced with a minimum 1/2-inch fastener. For example, Mark Williams does not offer axles in the 7/16-inch stud format and as a result, supplies all axles drilled and tapped to accept 1/2-inch or larger studs. Proper replacement studs are fashioned from high strength materials (often chrome moly steel) and are threaded all the way to the head. Because of this, the stud can be fully engaged in the backside of the axle. As mentioned above, 1/2-inch fasteners are the bare minimum starting point for wheel studs. Remember that the stud is the element that actually transfers the load to the wheel, and the wheel and tire are what transfer the load to the drag strip. And some of these loads at the axle might be much larger than you think. Look at the basic math (and I mean basic - there's nothing here that takes the tire "hook," track conditions or overall tire dimensions into consideration): Engine Torque x Torque Converter Multiplication x Transmission 1st Gear Ratio x Rear Axle Ratio = Load. Using a typical small block powered Stock Eliminator car, the loads can exceed 10,000 foot-pounds of torque at the axles. Arguably, there are two axles and ten studs over which to distribute this load, but it's still a bunch. Because of this, the vast majority of serious drag cars can benefit from the use of "drive studs." These are huge studs that measure up to a full 11/16-inch in diameter (on the drive shoulder). Designed to fit the holes in aluminum race wheels (i.e.: Centerline, Cragar, Weld, Bogart, etc.), the studs make use of an equally huge 5/8-18-inch axle thread (the portion of the stud which screws into the axle). Consider these components overkill if you like, but if bent or broken axle studs are plaguing your car, you need them. A good example of a quality drive stud is the MW piece shown in the following photo. These studs have 11/16-inch diameter shoulders for use with racing wheels. The drive stud is threaded into a 5/8-18-inch thread in the axle flange and secured with a jam nut. Wheels are held on with an open-end flanged lug nut with an aluminum washer. The drive studs incorporate a smooth shoulder (see the photos) that physically drives the wheel. In comparison, a street lug nut for aftermarket wheels has a built-in shoulder that drives the wheel. These street-oriented lug nuts are designed for use with small diameter studs (1/2-inch being the largest). In simple terms, the street models use much smaller diameter studs and the actual lug nut serves to drive the wheel. Obviously, this isn't the most efficient way to handle large torque loads. Next issue, we’ll dig deeper into drive studs. We’ll show you how to figure out the length of the stud along with the thickness of the respective washers you’ll need. Watch for it.

There are all sorts of different wheel studs and lug nuts available today. Choice is obviously plentiful, but some studs are better suited to certain tasks than others.

This is a conventional drag race replacement stud for the front of a production line automobile. The stud simply presses into the front wheel hub. This stud measures 7/16-20 X 2-7/8-inches, and is a replacement for a factory GM disc brake stud. The knurl measures 0.560-inch, and as you can see, the stud has a "bullet" nose to facilitate lug nut installation. It's perfectly acceptable to use this stud on the nose of your racecar. Just don't use a wheel spacer with this type of stud.

Mark Williams sells this 1/2-20 X 3-1/2-inch stud for use on the rear of a racecar. This stud (or probably more correctly, "bolt") screws in on the backside of the axle, and is held in place with a lock washer. When using studs such as this, it's a good idea to use Loctite or an equivalent thread cleaner along with a "most severe service" thread locking compound (use "red" Loctite on the bolt/flange only - not on the actual lug segment of the stud!). In the case of M-W studs, the bolt head on the backside of the stud must be torqued to 65 ft/lbs. If the fasteners are not installed correctly, the lug bolt head(s) could interfere with the rear brake cylinders. The installed torque of the wheel studs should be checked periodically. Wheel spacers should never be used with this type of stud.

Here's another stud type you might come across. Basically, it's a M-W piece that was initially designed for Winston Cup or GN competition. This stud has a "quick start" segment machined on the nose. As you've probably gathered, this allows the lug nut to be installed rapidly without cross threading. Again, this is more of a bolt than a stud, and it too is installed from the backside of the axle, using a lock washer for retention. This stud should only be used with the GN style quick start nuts or "acorn" type nuts. And yes, it is possible to use this large diameter (5/8") stud on a drag car, but it isn't recommended.

This is a conventional long 7/16 X 3-1/2-inch stud installed on the nose of a car. At this location of the car, a conventional open end lug nut is suitable since there is no driven load on the stud.

A drive stud (such as this M-W version) is designed with a 5/8-18-inch thread on each end with an 11/16-inch shoulder in between. Obviously, the shorter threaded segment is installed in the axle and secured with a jam nut.

Meanwhile, the shoulder (see the pointer) is the same OD as the lug hole ID in common aluminum drag race wheels. This ensures that the stud actually does the driving of the wheel, not the lug nut.

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