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Semi-trucks carry heavy loads across the country day after day, and we mostly ignore them. These behemoths of logistics have some interesting features and others that just make sense. Have you ever wondered why semi-truck wheels have different shapes? The front wheels are typically convex while the rest are concave; what gives?

Semi-truck wheels are shaped differently due to three practical factors

Semi-Truck Driving Down a Highway
Semi-Truck Driving Down a Highway | Wiki Commons

It might sound extremely simple, but sometimes the right answer is simple. If you add one and one together, you always get two. There’s nothing complicated about this at all. The same goes for the semi-truck wheels.

Jalopnik tells us the front wheels and rear wheels of these big rigs are different because of:

  • Packaging
  • Cost Saving
  • Common Sense

Let’s explore.

The front wheels are convex; why?

Convex Front Wheel on a Semi-Truck
Convex Front Wheel on a Semi-Truck | Wiki Commons

The front wheels do the steering for any vehicle. Although some cars and SUVs offer rear-wheel steering, this steering is limited to a small degree of change and is only meant to aid the front wheels. Because the front wheels handle the steering, there needs to be room to fit the steering joints, bushings, bearings, suspension, and brake systems required.

All of these items fit on the front axle, and the wheels are convex to keep the axle as wide as possible to offer maximum stability. Additionally, the center of the axis for wheel turn aligns with the center of the wheel and tire, or at least it’s as close as it can be. This is the right way to package the front wheels for the best performance in semi-trucks.

All rear semi-truck wheels help save money

Angled View of Rear Semi-Truck Wheels
Angled View of Rear Semi-Truck Wheels | Wiki Commons

It might be a little unbelievable, but the same reasons for the rear pairs of wheels on a dually pickup truck are the same as for semi-trucks and their trailers. Truckers get used to how these wheels are packaged, but most of us don’t know what’s done to make them work.

All rear axles on semi-trucks have pairs of wheels on each end. These wheels are identical but flipped around, creating the concave look of the outer wheels. Manufacturers attach the wheels this way allowing the two wheels to both attach to the same hub. This lower the cost associated with building these trucks.

For most commercial trucks, the rear wheels are identical to the front wheels, with the outer pair flipped around. This ensures fleet operators can buy several tires that will be used as required whenever one needs replacing. Semi-truck wheels could differ from one trailer builder to another, but they are typically the same.

Is the answer to the shape of semi-truck wheels really that simple?

Semi-Truck on the Road
Semi-Truck on the Road | Wiki Commons

Yes, it certainly is that simple. The packaging makes sense with the front wheels convex to make room for necessary components in a space where there is only one wheel at each end of the front axle. The use of single hubs for each pair of rear wheels cuts the overall cost of building and maintaining these big trucks and the trailers they pull. It’s an amazingly simple but sensible solution to what could have been a much more complicated conversation.

Next, learn why semi-trucks might be tailgating you, or enjoy this video below:

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