Spreading the load
Why Do Trucks Have So Many Wheels?
A loaded truck weighs as much as thirty cars. Its wheels are not for grip — they are for not destroying the road.
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Step 1 of 5
Pressure is weight divided by area.
The same load pressed through a small patch does far more damage than through a large one. That is why a stiletto heel dents a floor a heavy boot does not.
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Step 2 of 5
Road damage rises viciously with load.
Doubling the weight on an axle does not double the damage — it multiplies it many times over. Keeping each axle under its limit matters far more than the total.
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Step 3 of 5
So the law counts axles, not tonnes.
Legal weight limits are set per axle. A haulier who wants to carry more adds another axle rather than arguing about the total, and heavy loads sprout wheels.
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Step 4 of 5
Some of them lift off the ground.
An empty truck does not need all its axles, and unused wheels cost fuel and tyre wear. Lifting axles come down only when the load requires them.
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Step 5 of 5
Twin tyres are the same idea again.
Two narrow tyres side by side carry more than one wide one and fail more gracefully. If one bursts the other holds the corner up long enough to stop.
One heavily loaded truck does more damage to a road surface than several thousand cars, which is most of why road tax works the way it does.
The short version
A truck spreads its weight over many axles because road damage depends on the load each wheel presses down, not on the total.
Try it yourself
Press a pencil point into your palm, then the flat end. Same push, very different feeling.