ANDRA Fastlane ANDRA_FASTLANEED26 - Page 12

tech GO BIG! Nobody gives much thought to rear axle (or wheel) studs and lug nuts. If the parts meet the rules and the wheels don’t fall off when you’re knee- deep into the loud pedal, all is well, so the reasoning goes. But there are plenty of reasons to give these components some extra thought, not the least of which is safety. Keep in mind the axle stud is the component that actually transfers the load from the powertrain to the wheel. The wheel and tyre are what transfer that load to the pavement. The loads at the axle can be much larger than you might think. Check out this basic formula for load (and it is basic with a capital B—it does not take tyre “hook”, track conditions, or overall tyre dimensions into consideration): Engine Torque x Torque Converter Multiplication x Transmission 1st Gear Ratio x Rear Axle Ratio = Load For a typical small block-powered hot rod, the loads at the axles can actually exceed 10,000 foot-pounds of torque. Arguably, there are two axles and ten studs to distribute this load, but that’s still a bunch of load to handle. torque Why rear axle studs and lug nuts are more important than you think When it comes to rear axle studs, bigger is definitely better. A stock 7/16 inch (or equivalent metric size) GM stud is inadequate for competition use. These press-fit wheel studs have a knurl to secure them to the axle shaft’s wheel flange. Rear axle studs for racing are threaded all the way to the head, allowing the studs to fully engage the backside of the wheel flange. Axle studs for racing should measure at least 1/2 inch at the drive shoulder. Really serious, high-horsepower cars that use aftermarket axle shafts should use axle studs made specifically for drag racing. Called drive studs, their shoulders’ outside diameter is the same as the inside diameter of the lug holes in most aluminium racing wheels. This ensures the stud actually does the driving of the wheel, not the lug nut. You can get studs with drive shoulders up to 11/16 inch in diameter with an equally huge 5/8-18 inch axle thread (the portion of the stud that screws into the axle). The wheels are secured to the axles with open- end flanged lug nuts with aluminium washers. STORY AND PHOTOS BY WAYNE SCRABA The most important factor when selecting the proper axle/drive stud is that the driving portion 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. Washer thickness should be greater than the stud shoulder extending past the wheel. That means you must measure the thickness of the wheel center, the thickness of the brake hat (or drum), and the thickness of a wheel spacer if one is used to determine the stud length and washer thickness. Several manufacturers offer axle studs of various lengths (the length of the stud’s drive shoulder is what varies) and washer thicknesses. For example, the Summit Racing website lists more than 90 different 5/8 inch axle stud combinations, along with hundreds of other types for various drag race applications. Consider these components overkill if you like, but if bent or broken axle studs are plaguing your car, you absolutely need them.