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How It Works: Airless tires

airlesstires
© Jennifer Fravica, Driving

Although tires are what you see, your vehicle is actually riding on the air inside of them. That air supports the tire, keeps it on the rim, and cushions the ride.

Of course, if air goes in, it can also come out. That’s most obvious when something like a nail penetrates the tire and causes a flat, but tires are naturally porous and gradually lose a bit of air over time. Even if tires don’t look low, you should check their pressure once a month or so. A low tire will use more fuel, and can wear unevenly and need replacing sooner than one with the correct pressure.

So why not use tires that don’t need air? While it’s still in the early stages of development, Michelin presented a new concept last June, the Vision tire, which could pave the way for car tires that don’t need pumping up.

Unlike a regular tire, the Vision is created with a 3-D printer, constructed with an internal honeycomb web instead of an air chamber.

Bridgestone has also been developing an airless tire, and recently announced that the design may go on sale for bicycles in 2019. Hankook Tire is also working on an airless model.

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The Michelin Vision concept tire uses 3-D printing to create a honeycomb texture, with the tread printed onto the edge.

Airless tires certainly aren’t new. Wagons and early cars used wheels edged with metal bands or solid rubber. Scottish engineer Robert William Thomson invented a pneumatic rubber tire and patented it in 1845, but it was too expensive to be viable. John Dunlop came up with a successful one for bicycles in 1888, and seven years later, brothers André and Edouard Michelin created one for automobiles.

Solid rubber tires are still made, but they’re primarily used for low-speed, heavy-duty applications, such as on construction equipment or forklifts, or for lighter-duty use on lawn mowers, trailers and golf carts. On a car, they’d add too much weight and, without that cushion of air, they would transmit every bump and produce a very stiff ride.

In 2005, Michelin introduced an airless tire concept called the Tweel. The design combined the tire and wheel into a single unit, with a central rigid hub, an outer tread, and spokes in between. The polyurethane spokes were firm enough to support the tire, but flexible enough that they absorbed road shock to provide a more comfortable ride.

The Tweel concept wasn’t adapted for car tires, but in 2015, Michelin launched it for commercial applications on golf carts, industrial lawn mowers, and skid-steer loaders.

The Vision concept evolved from the Tweel, but Michelin says it intends to offer it as a passenger car tire. Rather than being made up of three separate units joined together as the Tweel is, it is created as a single piece. By using 3-D printing, engineers were able to create an open-weave honeycomb structure that is strong in the centre to support the wheel, but flexible toward the edges for ride comfort.

The outer tread is also applied with a 3-D printer, and Michelin says it could be reapplied once the tread wears down – conventional car tires must be replaced when this happens – or when a different tread pattern or compound is required, such as when switching for winter. The concept also contains internal sensors that monitor the tire’s condition, and can communicate with a mobile app to inform the driver or to make an appointment with a tire dealer.

The tire can potentially be made from a wide range of materials, and at the concept’s debut, Michelin suggested these could include plastic and electronic waste, paper, bamboo, cardboard, or recycled rubber. The Vision tire itself would be recyclable at the end of its life.

No one’s sure when such a tire might actually make it to market, since there are still many issues to overcome, such as the open weave trapping mud and snow. And while 3-D printing can create the intricate honeycomb that a mould cannot, as well as potentially build numerous tire sizes with just one machine, even the fastest printers currently available are still too slow for mass production.

Bridgestone initially showed an airless tire in Japan as a possibility for city-based microcars, but last April, unveiled the design as the basis of its Air Free Concept 1 bicycle tire. The airless tire uses spokes both as part of the wheel, and in place of an air chamber to support the tread.

Because the tire can’t puncture and lose its air, the cyclist doesn’t need to carry an air pump. That’s also a benefit to airless tires on a car: there’s no need for a spare tire, which adds weight at a time when automakers are trying to shave it off wherever they can to help improve fuel efficiency.

Technologies like the Vision tire’s sensors may also play a role in active safety features, especially on autonomous cars. Vehicles that can automatically brake themselves determine how far away they are from an object, but worn tires can dramatically increase the stopping distance. By knowing how much tread is left, the systems can better determine when to apply the brakes in order to stop in time.

This feature originally appeared in Driving.ca on July 26, 2017. Jil McIntosh is an automotive writer and reviewer for Driving.ca

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