Why Do Some Semi-Trucks Have Spikes On Their Wheels?

It can be an intimidating sight at first: a semi-truck with enormous spikes sticking out of its wheels, slowly sidling towards you in the next lane. They're spinning like a drill and look like they're about to carve up your vehicle, as if it's something out of a "Mad Max" film. Thankfully, that's not the primary purpose of these spikes.

Frightening as they may be, it's the position of the spikes which confirms its true purpose. Each is mounted atop a lug nut — the bolts holding the wheels onto the truck — where they act as protective covers from possible road hazards. Debris and other objects on the roadway can easily bounce up and strike a wheel, but the conical shape of the spikes means a glancing blow is less likely to cause real damage. Meanwhile, their pointed profile also avoids nooks and crannies into which water, ice, and snow could accumulate, and which over time might lead to rust on unprotected lug nuts. 

So the spikes aren't just there to look menacing, but if they cause you to leave more space, that's no accident either.

That you may find yourself wanting to move away from a semi-truck with long, protruding wheel spikes may not be their primary purpose, but it's still intentional. Driving a semi-truck is obviously no easy task, as the truck has difficulty changing speed as rapidly as a car and features numerous large blind spots that sometimes smaller vehicles can hover in for too long, endangering both in the process. If the spikes manage to catch your attention and cause you to give the truck more space where it needs it, that's a safety side-benefit for everyone on the road.

Unlike the tire slashers on James Bond's famous Aston Martin, the wheel spikes on a semi truck probably wouldn't be able to carve up your car even if the trucker wanted to. They're typically made from aluminum alloys and/or plastic and so would most likely simply scratch your car before breaking away. All the same, it's good to take them seriously, and perhaps driving would be a little safer and focused if every vehicle had wheel spikes. Probably not, though.