[FoRK] NYTimes.com Article: Autos on Monday | Technology: Reinventing the Wheel (and the Tire, Too)

khare at alumni.caltech.edu khare at alumni.caltech.edu
Mon Jan 10 12:22:12 PST 2005

The article below from NYTimes.com 
has been sent to you by khare at alumni.caltech.edu.

Just the thing for Indian roads -- they're right on; and I hadn't thought of the difference between stiffness in X, Y, and Z being impossible to distinguish in air-filled tires... Rohit

khare at alumni.caltech.edu

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Autos on Monday | Technology: Reinventing the Wheel (and the Tire, Too)

January 3, 2005



THE first automobile to use air-filled tires was a racecar
built by André and Édouard Michelin in the early 1890's.
More than a century later, the French company founded by
the Michelin brothers is so identified with pneumatic tires
that its mascot, Bibendum, is a man made of little else. 

Now, after decades spent persuading the world to ride on
air, the company has begun work on an innovation that could
render the pneumatic tire obsolete. Engineers at Michelin's
American technology center here envision a future in which
vehicles would ride on what they call the Tweel, a combined
tire and wheel that could never go flat because it contains
no air. 

Arriving at a conference room recently to explain the
development project, a research engineer, Bart Thompson,
used the Segway Human Transporter that he rode to the
meeting to illustrate his points. Aboard this high-tech
visual aid - one of those self-balancing electric scooters
best remembered for the optimistic claim that it would
reinvent personal transportation - Mr. Thompson whizzed
down the hallway and out to the lobby, pirouetting among
the benches and planters to demonstrate the flexibility of
the Tweel. 

To be sure, the Segway would be a very small market for
Michelin, the world's leading tiremaker, but it is an apt
demonstration vehicle for the Tweel. The first commercial
use of the integrated tire and wheel assembly will be on
the stair-climbing iBOT wheelchair, another product
developed by Dean Kamen, the Segway's inventor; Michelin
said it would announce another application at the Detroit
auto show next week. 

The tiremaker has high expectations for the Tweel project.
The concept of a single-piece tire and wheel assembly is
one the company expects to spread to passenger cars and,
eventually, to construction equipment and aircraft. 

The Tweel offers a number of benefits beyond the obvious
attraction of being impervious to nails in the road. The
tread will last two to three times as long as today's
radial tires, Michelin says, and when it does wear thin it
can be retreaded. 

For manufacturers, the Tweel offers an opportunity to
reduce the number of parts, eliminating most of the 23
components of a typical new tire as well as the costly
air-pressure monitors that will soon be required on new
vehicles in the United States. 

In recent years, manufacturers have devoted an increasing
amount of attention to tires that let motorists continue
driving after a puncture, for 100 miles or more, at a
reduced speed. Several such "run flat" designs are now
available, providing convenience and peace of mind for
travelers as well as freeing automakers to eliminate the
weight and cost of spare tires. 

Michelin, which markets run-flat tires under the Pax name,
took a different approach in developing the Tweel. Its
goal: a replacement for traditional tires that is designed
to function without air in the first place. 

Mounted on a car, the Tweel is a single unit, though it
actually begins as an assembly of four pieces bonded
together: the hub, a polyurethane spoke section, a "shear
band" surrounding the spokes, and the tread band - the
rubber layer that wraps around the circumference and
touches the pavement. 

While the Tweel's hub functions as it would in a normal
wheel - a rigid attachment point to the axle - the
polyurethane spokes are flexible to help absorb road
impacts. The shear band surrounding the spokes effectively
takes the place of the air pressure, distributing the load.
The tread is similar in appearance to a conventional tire. 

One of the basic shortcomings of a tire filled with air is
that the inflation pressure is distributed equally around
the tire, both up and down (vertically) as well as side-to
side (laterally). That property keeps the tire round, but
it also means that raising the pressure to improve
cornering - increasing lateral stiffness - also adds
up-down stiffness, making the ride harsher. 

With the Tweel's injection-molded spokes, those
characteristics are no longer linked - a point of
particular excitement to an engineer like Mr. Thompson
because of the potential it holds for improving handling
response. The spokes can be engineered to give the Tweel
five times as much lateral stiffness as current pneumatic
tires without any loss of ride comfort. 

The Tweel auto project is in its infancy - "Version 1.0,"
Mr. Thompson said - and only a single set of car Tweels
exist. A test drive in a Tweel-equipped Audi A4 sedan on
roads around Michelin's research center proved to be far
less exotic than the construction method or appearance
would suggest. The prototype Tweels are noisy, as Mr.
Thompson warned they would be, a problem traced to
vibration in the spokes. 

The Tweels also transmit more of the feel of a coarse road
surface than customers would tolerate in a production tire,
but the level is understandable considering the early stage
of development. More important, the steering's response as
the driver begins a turn is excellent, and large bumps were
swallowed up easily by the Tweels and the Audi's unmodified

There are other negatives: the flexibility, at this stage,
contributes to greater friction, though it is within 5
percent of that generated by a conventional radial tire.
And so far, the Tweel is no lighter than the tire and wheel
it replaces. 

Almost everything else about the Tweel is undetermined at
this early stage of development, including serious matters
like cost and frivolous questions like the possibilities of

Logical uses - military vehicles, for example - would come
years before automobiles, but Michelin's business
projections accommodate the possibility that the Tweel may
not be an overnight success. This would be nothing new for
Michelin: the radial tire it invented in 1946 was not
widely accepted in the United States until the 1970's. 



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