They’re small, often inconspicuous (sometimes overshadowed by a flashy or elegant wheel design, or hidden by a wheel cover), and taken for granted. But, and almost needless to say, they’re important.
Lug nuts, or wheel nuts, keep your wheels firmly attached to your car at all times. Your vehicle’s wheels may have four, five or six nuts, depending on what you drive. If they’re not installed properly, or they’re the wrong size–in the case of aftermarket wheels, or if you’re replacing broken or corroded nuts–it will usually mean they won’t lock onto the wheel correctly, will break more easily, and will cause the wheel to wobble or fall off completely. Loose or missing nuts will cause uneven pressure on the wheel hub and contribute to premature wear of the wheel bearings. And unnatural pressure will occur when your car or truck corners, brakes, or ramps up to higher speeds. All that is a scenario for certain danger or disaster.
Wheel nuts are key to the entire wheel mounting system, which, to work properly and safely, means that the wheels must make full contact with and fit flat against the mating surface of the hub.
The wheel mounting system is essentially a bolted joint that works by clamping two ‘mated’ surfaces together tightly. The friction of the two surfaces and the force produced by clamping them together with bolts creates a ‘clamp load’ that allows the surfaces to resist movement. That ‘clamp load’ is created by a very precise tightening of the bolts against the mated surfaces, a procedure usually measured in foot-pounds of torque, with a torque wrench. When you change or rotate your vehicle’s wheels, be aware that most underlying causes of loose wheels are linked to over-torquing or under-torquing the lug nuts.
(side note: Before 1975, Chrysler cars in the U.S. used left-hand and right-hand screw thread for different sides of the vehicle to prevent loosening. Other makes used both left-handed and right-handed lug nuts before 1965 models. But it was determined that the taper seat worked to prevent loosening, so modern vehicles use right-hand threads on all wheels.)
Wheel nuts come in a wide variety of sizes, styles, and materials including tapered lug nuts, ball seat lug nuts, and mag and screw-in lug nuts, depending on vehicle make, model, and whether it’s foreign or domestic (U.S.). And, of course, you can opt for specialty forged, CNC-machined-to spec, magnesium alloy lug nuts (visit https://smwwheels.com/about-smw-wheels/ for news and information about the world’s best forged mag wheels).
So consider what makes up a complete wheel nut fitting when changing out or rotating wheels or wheel/tire sets:
Thread pitch (a measurement of the distance between threads), the size of the studs (another name for those threaded bolts that stick out through the holes in the rims) that the nuts attach to on the car, and the seat type–the area where the wheel nuts contact the wheel’s surface.
These factors also differ according to car brands and models. If you’re doing a ‘nut job’ yourself, consult reliable online guides (e.g., the eBay home page for “wheel nuts”) or your vehicle owner’s manual to help you find the factory size you need. Or have it done by a knowledgeable mechanic.