Book 3, Question 21
Why Do Trucks Have So Many Wheels?
Trucks have many wheels to spread their heavy load over more of the road so it does not crack.
A loaded truck can weigh as much as many cars. Extra wheels spread that weight over more patches of pavement. More wheels share the weight, so the road does not crack!
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Quick answers
What wears roads most?
The weight carried by each axle, not the truck's total weight.
Sources: fhwa.dot.gov, ops.fhwa.dot.gov
From the book
Page from A Million Whys Book 3
More fun facts
- How much a truck wears down a road depends mostly on the weight carried by each axle, not the truck's total weight.
- Groups of axles close together spread the load along the pavement.
- That lets a truck carry more weight with the same or less road damage than one heavily loaded axle.
- On U.S. Interstate highways, a single axle may carry up to 20,000 pounds.
- A tandem, two axles close together, may carry up to 34,000 pounds.
- The usual top weight for a whole truck on the Interstate is 80,000 pounds.
- Axles less than 40 inches apart count as a single axle under the rules.
Sources: fhwa.dot.gov, ops.fhwa.dot.gov
Questions kids ask
How heavy can a big truck be on the highway?
On U.S. Interstates the usual limit is 80,000 pounds, spread over many axles and wheels.