Seriously, why aren’t tires made of solid rubber? – Jalopnik

Hello, construction and agriculture professionals, we are not talking to you at the moment. This discussion is not about forklifts, excavators or solid tire skid steers. We’re talking about why cars and trucks use pneumatic (aka air-filled) tires, not rubber several inches thick, because we’d all like to stop dealing with flat tires, thank you very much. But as long as we recognize that industrial equipment often uses solid rubber tires, let’s discuss why.

If you have a 100,000 pound wheel loader, pneumatic tires can burst like bubble wrap. Industrial vehicles that have to navigate construction sites with screws and nails lying around or navigate the concrete of a warehouse at walking pace can get away with tires that are simply rubber from rim to road. Solid tires have fantastic longevity, experience little wear, have low rolling resistance and resist the scrapes or punctures that would give pneumatic tires a new life as playground swings.

However, cars and trucks treat tires very differently. When you turn, part of what keeps you from sliding into the weeds is the tire’s contact patch staying flat on the road. Modern radial tires have sidewalls that deliberately deform to allow the tread to touch the street, rather than riding on the edge of the tire. This is why radial tires were such a technological leap over bias-ply tires. Those now-gone white-walled bias plies had exceptionally stiff sidewalls that allowed them to act as one solid unit with relatively little deformation, causing the tires to bog down over the smallest bumps and lose whatever grip they had. Now take these negative properties and multiply them exponentially once you replace air with more rubber.

But let’s say you’re only interested in driving on a smooth track and you can handle the tough ride. Solid rubber is still a terrible solution. Rubber is much heavier than air, and with solid rubber tires you would add a lot of rotating mass and unsprung weight to your wheels. The result is that you hinder acceleration and cause any bumps you encounter to bounce the wheel into the air much more than with a softer pneumatic tire. Imagine installing lightweight wheels, then slapping on fat, dense, heavy tires. Can those tires be made exceptionally thin to save weight? Certainly! Then all the shock from bumps will go straight to the rims, likely causing them to bend. And curb damage will be virtually guaranteed.

The point is that we have known about the disadvantages of solid tires for hundreds of years, because there were no air-filled tires before 1847. Then Scottish inventor and engineer Robert W. Thompson invented pneumatic bicycle tires. Until then you could probably feel through the steering wheel whether the coin you were driving over was heads or tails.

This isn’t to say manufacturers aren’t working hard on airless tires, they’re just not solid rubber. Check out Michelin’s “Tweel” tires, which use a series of rubber mounts instead of an air cushion to keep the tread in contact with the surface. But while flat tires are ubiquitous in the mower, ATV, forklift and industrial equipment markets, they are not yet found on cars. There are still major issues to overcome, such as heat build-up, noise, weight, the need for manufacturers to redesign them and safety regulations. For now, all you have to do is keep that jack and the space-saver spare in your trunk.