Eli5: Why are car tires filled with air and not just made completely of rubber?


Eli5: Why are car tires filled with air and not just made completely of rubber?

In: Engineering


Air provides a cushion on which the tire can absorb impact, move laterally in turns, and decreases rolling resistance. If they were solid rubber, they would have very little pliability, would be extremely heavy, and wouldn’t be able to be patched/repaired. I’m sure they would be a great deal more expensive too. Google “tweel” to learn more about alternative to air tires.

A fully rubber tire would be heavier.

A heavier tire means it takes more energy to make it speed up, but also more energy to make it slow down. This means that it will take a longer distance to brake.

In addition, the air in the tires acts to absorb minor bumps in the road, along with your shocks. Solid rubber tires can’t really deform as much, so you’ll feel every bump full on.

Also, they would be significantly more expensive.

There are actually designs of no-air rubber tires, so it is a relevant question. There are several factors:

Cost (current design is cheaper)

Performance: most people don’t stop to think just how awesome is that tires can take a beating for literally thousands of km. It’s harder for no air tires to retain their properties for so long. Also it’s hard to beat air tires in shock absorbance.

Your tire is an air spring that softens the ride and allows the tire to deflect – to bend to the shape of the road, increasing surface contact and thus traction. By being solid, deflection would be minimized and traction would be greatly reduced, and the rid would become very uncomfortable.

Further, the weight. Not only would such a tire be outrageously heavy, but it would put additional strain on the materials used to hold the tire together, as well as on the suspension. Just keeping that much rotating mass attached to the car would require much, and I mean much larger structural suspension components, which would make the car heavier. You’d need larger springs, larger shocks, and they’d all take on WAY more load and wear. You’d need MUCH larger brakes, and they’d be drum brakes like you’d see on a semi, just to stop your car, which comes with more weight and greater maintenance and material costs. It would take a lot more energy to accelerate the vehicle, you’d generate a lot more heat just trying to stop it, and you’d have lots of problems with inertia, not just within the wheel itself, but also in suspension travel, and the whole car. Your fuel economy would tank.