Michelin Tweel: Full Circle
By Bill Moore
Prior to John Dunlap's creation of the pneumatic tire over a hundred years ago to make bicycle riding a less jarring experience, wheels were rigid and inflexible. Springs and one's posterior were the only means of softening the unforgiving ride over rutted tracks and cobblestones that were the roads and streets of the time.
By the turn of the 20th century, the horseless carriages of the period where being equipped with enlarged versions of the original bicycle tire. Now, with the exception of steel train wheels, nearly every means to conveyance rides on a pressurized cushion of air held fast in a donut of high tech synthetic rubber. And while tires have improved dramatically over the last century in terms of reliability and performance, they still go flat. In fact, problems with tread separation and inflation levels nearly destroyed another early pneumatic tire innovator, Firestone, in the wake of the Ford recalls of millions of tires on Explorers.
So, why not come full circle and reinvent the tire by eliminating the air-filled donut?
That's precisely what Bart Thompson and his colleagues at Michelin's North American research center did and what they came up with could someday become the “Tweel of Tomorrow.” As is obvious from the photo, the Tweel relies on a series of radial spokes that provide it with “vertical compliance” -- meaning shock absorptive flex and motive torque. According to Thompson these spokes can be engineered to specific applications, though it isn't yet ready for racing circuit.
Not coincidentally, the Tweel was an outgrowth of work that Michelin was doing on “run flat” tires, which because of their stiffened sidewalls allow a driver to drive to the nearest exit if his tire goes flat rather than having to immediately pull off the road. It was during a conference on run flat tires in the late 1990s that the comment was made that if you lessened the load on the tire enough and reduced the speed sufficiently you could “basically run forever.” That clicked on a light in someone's head at Michelin and the Tweel project was initiated.
But to do so meant throwing out everything they knew about building tires, something Michelin as been doing well for a very long time.
“We're going to develop new materials. We're going to develop new intellectual property. We're going to develop a new manufacturing procedure to make an object engineered from the ground up to provide the same functionality as a tire but without the air.”
The Tweel consists of four basic components, a fairly standard tread layer like you'd find on just about any conventional car tire, a specially reinforced and patented tread band that is attached to the center hub by the flexible spokes.
What this translates into is a tire that can become much more of the vehicle's suspension system than current technology.
Thompson illustrated this by pointing to a low speed electric car like the GEM. He explained that he could essentially eliminate the need for a suspension system on the vehicle just by how the Tweel is engineered. The first product on which the system will appear will be a small Bobcat-type earthmover, in part because the company feels confident it has sufficient engineering maturity for this type of low-speed application.
“We envision being in the market with that in a three year time frame.” (12:11).
He does concede that Michelin's engineers are “infants” still when it comes to understanding Tweel. For example, he and his colleagues are still researching how to manufacture it for high-speed operations.
“We are definitely continuing to investigate and we see no major technological hurdles,” he said.
But this is not, in Thompson's words, “a revolution that will happen overnight.” He pointed out that it took 25 years from the the introduction of the steel-belted radial tire in France before it became the accepted tire of choice here in the United States.
He also observed that “innovation is a messy business” especially when it is as disruptive as the radial tire was in its day.
In the case of the Tweel, it will involve not just a an airless tire, but an entirely new business model.
Instead of replacing the entire tire, you will buy a Tweel-equipped car that will be good for the life of the vehicle. Michelin thinks it will only need to replace the outer wear tread, somewhat akin to re-souling a shoe. He explained that today when we replace tires, we throw away 80 per cent of the volume of that produce.
“You just wear out the rubber that hits the road.”
He also believes that the process will take no longer than it would take to do an oil change.
This would, of course, mean huge savings on the billions of scrap tires that are piling up around the world.
Thompson acknowledges that oil prices and availability are also a factor in Michelin's thinking. Current tires dependent heavily on synthetic rubbers derived from petroleum, whereas the Tweel can be made a wide range of elastomeric materials, but he also notes that many of these materials are not part of the company's current “tool kit.”
“From the long term, I believe that we can, to some extent, get away from just petroleum-based products because the physics of our invention are different from the physics of the pneumatic tire. “
Besides experimenting with applications like the Segway Centaur and the small earthmover, Michelin has also mounted the Tweel on Audi A4. Thompson commented that the wheel-tire combination provides significantly improved handling “in terms of very quick response and linear response.”
“The reason for that is that we can independently change the lateral stiffness -- that correlates well to handling – from the vertical stiffness, which correlates to comfort. So, basically you can take a sedan and turn it into a golf cart. It's like corning on rails... It's a very firm, positive response, laterally. So... you can have the best of both worlds. That's the way we're trying to have it, with a comfortable ride [and] a quick, sporty response.”
While Michelin hasn't driven the test Audi A4 at high speeds, they have tested the Tweel in their lab at speeds up to 120 mph (200km/hr).
And what about rain and snow?
Thompson replied that there is no difference between the Tweel and a conventional tire on rain-slick roads, but his lab has not tested it in snow.
He concluded by saying that there's been a lot of interest on the part of car makers. It is that level of interest and support which will largely determine the pace at which Michelin will commercialize the produce. But for the time being, Michelin is assuming it will be another 10 to 12 years before you'll see Tweel-equipped cars appearing in showrooms.
You can listen to our complete conversation by using the MP3 Player in the right-hand column or by downloading the file to your computer hard drive for play back on your favorite MP3 device. The download url is: http://www.evworld.com/evworld_audio/michel_tweel.mp3.