Why Do Trucks Often Have Chains Hanging Underneath?

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Trucks have features and capabilities that cars don’t, so they always carry accessories you don’t find on other vehicles. You may notice, truck chains, a set of chains dangling from underneath the truck’s body, usually near the rear axle. Most of the time, these are there for practical reasons.

Trucks often hang chains underneath for slick and snowy road conditions. Drivers will put chains underneath their tires to help them gain traction. In addition, certain vehicles use chains for safety reasons, as chains ground the vehicle and discharge electricity that builds up due to friction.

If you see another truck with chains underneath, they generally have a purpose. I’ll explain the reasons in more detail. 

Trucks have extra features that cars don't

Reasons Trucks Keep Chains Underneath Them

Some drivers may have unique reasons for keeping chains underneath their vehicle, but the two popular reasons are:

  • Chains help the vehicle gain traction in snow and ice.
  • Chains discharge static electricity. 

I’ll explain each of these below. 

Truck Chains Help the Vehicle Gain Traction in Snow and Ice

Drivers who live in places where snow falls understand how difficult it gets to drive in the weather. Things get scary when your vehicle loses traction, and you’ll quickly find yourself sliding across ice patches or getting trapped in snowdrifts. 

Trucks are naturally more capable than cars in these conditions, but that doesn’t mean they couldn’t use some extra help. Sometimes the chains you see underneath the vehicle are being stored for use in the winter months. 

When vehicles get stuck in ice and snow, the tires have nothing to grab onto, so they spin in place. Wedging chains underneath the tires helps them gain traction, and rather than spin in place, they’ll roll over the chains and move the vehicle forward.

Sometimes these chains are loose and used whenever needed, but drivers might also carry snow chains that wrap around the tire to provide constant traction for short trips. 

A third possibility, and perhaps the most likely one, is that the chains are part of an automatic traction control system. 

Automatic Traction Control (ATC) Devices

Heavy-duty trucks, commercial vehicles, and public transportation vehicles, among others, often have automatic traction control systems underneath. 

These devices are installed on the vehicle’s axles near the tires, and they deploy automatically when you are driving on slick roads. A mechanical arm unfolds and slings the chains underneath the tires while the vehicle is moving, providing them with constant traction control. The chains help prevent the vehicle from sliding, ultimately making driving safer. 

Here’s a YouTube that shows devices in action:

Some Areas Require Chains/Traction Control Systems

Some states have “chain control” areas and require vehicles to install chains due to the road conditions. 

Usually, these areas exist in mountainous regions where snowfall is frequent and roads are steep. Chain control areas have very low-speed limits, and the tire chains help drivers maintain traction and avoid dangerous accidents. 

In many places, snow tires are an acceptable alternative to tire chains, but automatic traction control systems may not be enough. 

Truck Chains Discharge Static Electricity

The other reason you might find chains dangling from a traveling truck is that trucks sometimes need to discharge built-up electricity. 

Flowing air and moving liquid create friction over the objects they flow through or against. Friction builds up around truck tires, inside tanks, and inside fuel pump hoses, among other places. This build-up leads to electrical sparks, which can result in fires or explosions, depending on the vehicle’s contents.

Chains used for this purpose usually drag along the roads to keep the vehicle grounded. The ground connection redirects any built-up voltage to reduce the risk of electrical hazards. Essentially, the chains are a safety precaution, and doing this is helpful in two scenarios:

  • Traveling with flammable items: Vehicles that transport or carry flammable gases and liquids often drag chains to keep the vehicle grounded. Gas is extremely dangerous when ignited, so these chains reduce this possibility. 
  • Frequent use of radio communications: Some also say that the built-up electricity can create static on a vehicle’s radio. Grounding the charge with a chain helps improve radio communication, which is essential for emergency vehicles and others that communicate with this system.

Chains are particularly useful for trucks loading/unloading or refueling. While the risk of a fire may be low, the ground connection provides additional safety when the stakes are high. 

Usually, one chain is enough to accomplish this, and you’ll only see it on one side of the vehicle. If you see a truck with chains near both rear tires or all four tires, these are most likely part of a traction control system. 

Types of Vehicles That Drive With Chains Underneath

Pickup trucks may carry chains around, but they are especially common on commercial vehicles, emergency vehicles, and large passenger vehicles. Some examples include:

  • Ambulances
  • Fire trucks
  • Petroleum trucks
  • Tanker trucks that transport flammable liquids
  • School buses
  • Box trucks

When carrying precious cargo, safety is a number one priority. Vehicles that have flammable gases, petroleum, or people onboard need to be extra careful to avoid a disaster and may decide that chains are necessary to discharge any electricity that builds up. 

For some, dangling chains create other hazards, so some companies will find other ways of dealing with this issue.

That said, all of these vehicles may have to travel in the snow, so it’s equally possible they have traction control devices installed. 

Chains help vehicles gain traction on rough terrain

Conclusion

Traction control and static electricity discharge are the two most common reasons trucks have chains underneath them. Sometimes these chains are loose, and other times, they are part of an automatic traction control system fixed to the vehicle’s axles. 

Truck chains used for traction control usually appear near the tires, whereas chains used for grounding are placed on just one side at the rear. 

You’ll see these on pickup trucks, but they are also very common on larger vehicles, such as snowplows, school buses, and emergency vehicles. 

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