Name: Why Do Some Truck Tires Don't Touch The Ground?
Uploaded: 2026-01-23T21:01:30.000Z
Duration: 4 min 49 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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Have you ever been driving down the highway,

looked over at a massive dump truck or a cement mixer and noticed something wrong?

You see the massive wheels spinning, the heavy frame rattling.

One entire row of them isn't even touching the ground.

They're just hovering there, spinning in the air, ghosting along the pavement.

At first glance, it looks like a mechanical failure,

It is actually a brilliant piece of engineering that saves billions of dollars in road repairs,

saves the trucking company a fortune in fuel,

and stops the truck from destroying itself during a turn.

Today, we're looking at the surprising reason why some truck tires are designed not to touch the ground.

Right here in Simple Things: Surprising Histories.

To understand the floating wheel, we first have to look at the road beneath it.

Concrete and asphalt are strong, but they have a breaking point.

If you put too much weight on a single point,

you don't just drive over the road - you crush it.

This is why governments enforce strict act axle weight limits.

It's not just about how heavy the entire truck is.

It's about how that weight is distributed.

If you walk in high heels, you sink immediately.

But if you wear snowshoes, your weight is spread out over a larger area,

This is exactly what that extra set of wheels, technically called a lift axle, is for.

When a dump truck is fully loaded with 20 tons of gravel,

that weight is too much for just two or three standard axles to handle legally.

huge airbags inflate, pushing that hovering axle down until it hits the pavement.

The weight is distributed across more tires, the pressure on the road drops,

and the truck becomes legal to drive without destroying the asphalt.

So if more wheels mean better weight distribution and safer roads,

The answer, as is often the case in history, comes down to money.

Big rig tires can cost hundreds of dollars each, and they wear out quickly.

Every mile a tire rolls against the pavement creates friction.

The more tires you have touching the ground,

the harder the engine has to work to push the truck forward,

Imagine a truck has just dropped off its load.

If the driver leaves those extra axles down,

they are just burning fuel and wearing down expensive rubber for no reason.

By lifting them up, they instantly reduce rolling resistance.

Many highways and bridges charge trucks based on the number of axles touching the ground.

a driver can legally classify the truck as a smaller vehicle,

There is one final crucial reason for the lift.

When a truck with multiple fixed axles tries to turn a tight corner,

They get dragged sideways across the pavement.

It screams, it shreds the tires, and it puts massive stress on the truck's frame and suspension.

If a truck has too many wheels on the ground,

it essentially wants to drive in a straight line forever.

By lifting that extra axle, the driver effectively shortens the truck's wheelbase.

It allows the truck to pivot smoothly around corners,

navigating tight construction sites or city streets without ripping the tread off the tires

So, the next time you see a truck with a ghost wheel hovering in the air,

balancing the laws of physics with the laws of the road and the cost of doing business.

I hope you enjoyed this slice of engineering history.

and subscribe to Simple Things: Surprising Histories for more stories about the everyday world around us.

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Why Do Some Truck Tires Don't Touch The Ground?

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