Most racers are intently focused on generating maximum horsepower and getting it to the ground. Often overlooked are those wheel studs that are subject to shear loads upwards of 30,000 psi in an 11,000 horsepower nitro car and over 15,000 psi in a doorslammer.
To lend their expertise to the subject we contacted two firms that collectively have over 100 years wheel stud experience: ARP and Mark Williams Enterprises.
Back in 1974 Williams developed the basic setup for professional-class cars that’s been successfully employed ever since: a beefy 5/8-inch screw-in stud that’s retained on the back side with a jam nut and features an even bigger 11/16-inch shoulder to accommodate aluminum drive wheels. This centers the wheel on the stud instead of being dependent on the taper of a lug nut. However, given the wide variety of wheel flange thicknesses on the market, and the desire to minimize rotational weight, there are many variables to consider. But first, let’s examine non-shouldered studs.
ARP’s forte is manufacturing application-specific press-in wheel studs with 7/16-20, ½-20, M12 x 1.50 and M14 x 1.50 thread pitch. There are over three-dozen dedicated stud part numbers in the latest ARP catalog. Also available from ARP are screw-in studs (1/2-20) for aftermarket axles in a variety of lengths, plus an M12 x 1.50 stud with an overall length of 2.955-inches.
Far superior to OEM offerings, ARP’s studs are manufactured from 8740 chrome-moly steel alloy and heat-treated to 190,000 psi tensile strength. They are cadmium plated for extra durability.
Installing press-in studs is fairly straightforward, however, the ARP studs are made with an interference-fit for the knurls and if the hole is too big the stud can spin. This is why virtually all aftermarket racing axles and hubs employ screw-in studs.
For anyone contemplating modifying OEM axles to accommodate different studs, or drill hubs, detailed instructions can be found in ARP’s catalog (a free printed copy is available upon request).
M-W’s shouldered drive studs are available in both steel and titanium. A typical installation includes the 5/8-18 stud and a jam nut to secure it, with the wheels held in place with an open-end flanged nut and an aluminum washer to prevent any marring of the wheel.
Titanium studs are available, and are about 45-percent lighter than comparably-sized ones made of steel. That’s an important consideration for a racer striving to minimize the rotating mass. However, the improved performance comes at a price, as titanium studs are roughly triple the cost of their steel counterparts.
Selecting the proper length drive stud is obviously important; the drive shoulder of the stud should be fully engaged in the wheel. M-W recommends that the unthreaded shank of the stud be slightly greater than the combined thickness of the brake hat or drum and the wheel. The washer should be thicker than that portion of the shoulder that extends past the face of the wheel.
To simplify the installation of any type of stud (wheel or otherwise) and mitigate the chance of harming threads or the stud shoulder, M-W offers a special stud installation tool that accepts a variety of collets that range from 5/16-24 to 5/8-18.
You wouldn’t think the lowly lug nut would be the focus of much attention, but Williams has developed a highly efficient setup that features encapsulated aluminum washers in various thicknesses from 3/16- to 3/4-inch to compensate for different wheel and brake hat combinations and prevents damaging the wheel. The steel Snap-Lock base nut is employed in lieu of a standard flanged nut, with four washer options.
For those intent on absolutely minimizing weight M-W offers integral aluminum nuts made from 7075-T6 aluminum and hard anodized. An integral aluminum washer snaps onto the nut and spins freely. While they’re part of M-W’s titanium stud package, they can also be used with steel studs.
So there you have it…information you can use to help make your race car’s drivetrain “bulletproof.” What’s more, both ARP and M-W have experienced tech teams that can provide personalized assistance with toll-free convenience.