Picture this: you’re driving down the highway and about to pass a semi-truck (on the driver’s side, at a reasonable speed, because that’s safer). And as you’re passing the cab, you see those large wheels rolling beside you. And the front ones are covered in spikes. If you’re like me and worry about what would happen in an accident, these spiked wheels seem unsafe and mortifying. So why are they there?

The spikes on semi-trucks serve a practical purpose

Underneath each of those spikes is a lugnut, which keeps the wheel on the actual truck. Over hundreds of thousands of miles of highway driving, those lug nuts are bound to wear out. And a worn-out lug nut can lead to a truck wheel falling off, causing major accidents. To prevent this, the spikes protect the lug nuts from the elements.

The spikes also help keep moisture away from the wheels in general. If you know anything about water, it’s that, when paired with metal, it can create rust. The spikes will flick that moisture away as the wheel spins. Many trucks protect their wheels from the elements in some capacity, whether it’s with flat plastic covers or truck spikes.

However, that’s where the mechanical benefits of truck spikes end, and the psychological advantages begin.

Truck spikes are intended to intimidate

Accidents with big rigs are, more often than not, fatal. Maybe not to the truck driver, but absolutely to anyone who ends up in front of them. A key to staying out of semi-truck accidents is to give them plenty of space. Keep a safe following distance on every side of them, and stay out of their blind spots.

Likewise, these spikes are used to deter drivers from veering into their lane. And in most cases, you’ll only see these spikes on the very front wheels. That happens to be exactly where the trucker’s biggest blind spot is: right on the side of the semi-truck. So those spikes keep you away from where a truck driver might not see you.

One could argue that intimidation isn’t the best way to prevent an accident. After all, driving stressed or with a clouded mind leads to mistakes and, inevitably, crashes. But beyond that, the spikes are used to give the truck some character.

In short, truck spikes are cosmetic more than anything

Semi-truck drivers could use just about anything to cover their lug nuts. But they give their truck a bit of personality or, at the very least, a dominating presence on the road. But if you’re spending 70 hours a workweek in a truck, the least you can do is make it your own.

There are only a few states that have certain restrictions on these decorations. Hawaii says that it can’t extend 4-inches past the wheel rim, and Washington state says the spikes can’t stick out from the vehicle’s sides if you’re looking at it from above.

But these decorations aren’t just for semi-trucks. If you want to protect the lug nuts of your car, and don’t mind looking a little silly in the process (spikes don’t really belong on tiny passenger cars. Maybe pickup trucks), then you can buy a set of wheel spikes for your own vehicle. And it’s perfectly legal!

So now you know why trucks have spikes. They were put there to scare you off, but they also protect the wheels and look pretty cool. So don’t mess with the trucks, or you’ll get the spikes.