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Last issue, we introduced you to several different wheel stud formats. We ended with a look at the best system available for a drag car: the drive stud. This time around we’ll explain how to figure out which stud fits what application and which washers to use for your application. Here’s how it works:
What gets confusing for a lot of racers - even Pro racers have been baffled by the combinations - is the number of different combinations of stud lengths and washer thicknesses available. Mark Williams offers a number of different washer sizes and stud lengths (the drive shoulder length of the stud differs). The reason for the multitude of combinations is the range of wheel center thickness on the market, coupled with the actual thickness of the brake drum or disc brake hat and a wheel spacer (if one is used). According to Mark Williams, the most important factor when choosing the proper stud is that the driving portion of the stud is fully engaged into the wheel. The smooth "drive" segment dimension of the stud needs to be slightly greater than the combined thickness of the brake adapter/drum and the thickness of the wheel. Meanwhile, the washer thickness should be greater than the shoulder extending past the wheel. When ordering a set of drive studs, you must specify the wheel center and brake hat (or brake drum) thickness.
In conjunction with their drive stud system, MW has developed a reduced hex (7/8") "Base Nut" series for use with the drive stud wheel retention system. The "Base Nuts" are produced in both 17-4 stainless steel and titanium alloy. The aluminum spacer washer attaches with a snap fit over the base nut; the washer spins freely, but will not separate from the nut, which in turn prevents marring of the wheel surface. This also eliminates the problem of losing the washers when swapping tires. The washer is available in different thickness (1/8" to 3/4") to compensate for different wheel and brake hat thickness. The washers can be changed if the wheel thickness changes. By using stainless steel and titanium alloys, rust or corrosion problems are obviously eliminated. These nuts are either produced on CNC machines from bar material or are forged. This makes the nut a dimensionally (and visually) superior component. Because of the manufacturing method, the thread pitch diameter is extremely square with the flange. This produces an even grip pressure load on both the wheel and the stud.
What if you're weight conscious? You can use drive studs manufactured from titanium alloy. As an example, Mark Williams manufactures drive studs machined from the lightweight material. These titanium studs are manufactured from Ti-17 material with a tensile strength of 180 KSI and a Rockwell hardness of 40. In comparison to a comparable chrome moly stud, the titanium piece actually features a higher tensile strength. Typically, a set of titanium studs can save approximately 1.625 pounds over a set of their conventional drive studs, but be prepared to pay for the weight loss. Titanium isn't cheap (nor is it easy to machine). As a result, titanium studs can increase the cost factor by well over one hundred dollars. Remember though, that unsprung, rotating mass is much more critical than just weight.
In addition to titanium studs, Mark Williams has also developed a set of "encapsulated" aluminum series lug nuts. Obviously, they're designed for applications where every ounce of weight is critical. The part is produced from 7075 aluminum alloy with a hard coat finish. The stainless steel washer spins freely, but will not separate from the nut. The nut has a fixed counter bore depth that is equivalent to using the standard nut/washers in combinations in the 1/8" and 3/8" thickness. The washer snap-fits on the nut to prevent accidental loss and is manufactured from rust proof stainless steel material.
As you can see, lug nuts and wheel studs are components that should not be taken lightly. More than one car has been mortally wounded simply because the owner turned into Scrooge on elementary hardware such as this. In the photos that follow, you'll find a selection of different stud and nut combinations, along with information on how to determine the right wheel stud/lug nut mix for your racecar.
A number of different drive stud combinations are available. That's one reason why some racers are confused over selection. Here's the drill: The various race wheels available all have different center section thickness. In addition, each brake drum or disc brake hat might have a different thickness. By offering different drive stud dimensions, almost any combination can be covered (including one with a wheel spacer).
Basically, the segment of the stud that threads into the axle is the same on all five drive studs offered by M-W (it has a 5/8-18-inch thread and is 13/16" long). The shoulder segment lengths vary, as do the wheel nut segments.
In conjunction with the drive studs, M-W also manufactures a series of reduced hex wheel nuts. These nuts have a hex head size of 7/8" and are designed for use with M-W washers. Not shown are titanium nuts and aluminum lug nuts. More on the washers in the next photo.
The washers used with the reduced hex nuts are designed to snap onto the nut. The snap fit allows the washer to spin freely as it is tightened against the wheel, preventing marring of the wheel surface. But at the same time, the washer won't separate from the nut when it's loose. This means you won't lose the washers when you change wheels.
The washers are available in a number of different sizes. The aluminum washer thicknesses are as follows: 3/4-inch, 9/16-inch and 3/8-inch. In addition, a 1/8-inch thick steel washer is available. Why have so many different washer sizes? Simple. Pretend you outfit your racecar with drive studs and then decide to change wheels. If the "new" wheel has a different thickness than the old jobs, remember that the drive shoulder of the stud might not be the appropriate length for the wheel. If that's the case, it's a simple (and cheaper) matter to buy different lug nut washers instead of changing studs.
Here's how to figure out which drive stud and washer combination is right for your car. Measure the thickness of the brake drum or the disc brake hat. For comparison's sake, let's say our fictitious hat measures 0.300-inch. Next, measure the wheel center thickness. In this case, the race wheel measures 0.525-inch thick at the center. This means we need a bare minimum drive shoulder dimension of 0.825-inch on the drive stud. It's important to have a drive shoulder that's a bit larger (in length) than minimum, so we specify a drive stud with a 7/8-inch (.875-inch) shoulder. When a standard nut is used, a longer shoulder is used to center the washer. The snap nut is self-centering.
This is a “decorative” chrome lug nut used on street driven cars. With this setup, the shoulder of the lug nut drives the wheel, not the stud. This is not a race car piece, folks.
