welcomia/Getty ImagesDriving alongside a semi-truck is unsettling at the best of times. They take up nearly the entire lane, can be difficult to see around, can trigger nightmares for anyone who has watched Final Destination, and some even have those intimidating, long, pointed spikes sticking out from the wheels.They don't look like standard lug nuts seen on a passenger vehicle, so what are they and what are they used for?Learn why some semi-trucks have wheel spikes, what sits underneath them, what those spikes actually do, and whether they serve a safety purpose.Why Do Semi-Trucks Have Spikes on Their Wheels?The long spikes usually seen on the wheels of a semi-truck are decorative covers designed to go over the existing lug nuts. They aren't designed to interact with the axle, tire, or braking system, and they don't hold the wheel in place.AdvertisementAdvertisementThey also don't only come in spike shapes. Manufacturers of these covers sell them in a variety of designs, like flat, bullet, rocket, or spear styles. They're usually made out of chrome-finished plastic, but metal options are also available. Like other lug nut covers, they can also put a barrier between the hardware and dirt or moisture, though the pointed shape itself doesn't provide a special protective function.Covers might attach by pushing onto the existing lug nut, or attach another way depending on the brand. Check the item's instructions when installing.Are Semi-Truck Wheel Spikes Legal?Plenty of decorative automotive accessories are either straight up illegal or in a legal gray area. So, what about wheel spikes?Federal commercial vehicle rules address wheel condition and secure fasteners, while individual states can place additional restrictions on items that project from wheels.AdvertisementAdvertisementFor instance, Washington state restricts certain wheel nuts, hub caps, and wheel discs that extend outside the vehicle body and create a hazard to pedestrians or cyclists. Rules can vary by state, so before buying covers, consider local vehicle-equipment laws in the area.These covers also shouldn't be confused with other dedicated wheel-safety equipment. The Federal Motor Carrier Safety Administration requires commercial vehicle wheel nuts and bolts to remain secure, and decorative covers don't replace inspections or maintenance.If a driver is concerned about safety while traveling beside a semi-truck with wheel spikes, the covers don't call for any special precautions. Drivers should follow the same advice recommended around other large trucks, including avoiding their blind spots and leaving enough room when passing.So the next time you see these wheel spikes, you'll know what they're for.SourcesWashington State Legislature, "RCW 46.37.369"ECFR, "Part 571—Federal Motor Vehicle Safety Standards"Federal Motor Carrier Safety Administration, "Tips for Passenger Vehicle Drivers"