A rolling revelation?

Michelin's PAV tire, with its coke-bottle sidewalls and vertical mounting, leads not only to improved handling, but also advantages in wet traction, rolling resistance and extended mobility. Don't look for it anytime soon, though.

Upon approach, you can tell that there's something different about this tire. It doesn't look like a normal tire&emdash;oh yes, it's still round, of course, but the sidewall shape seems extremely odd, a sort of half-coke bottle shape that flares as it touches the wheel, whose diameter is different on the inside than on the outside. The wheels themselves are different; modular aluminum designs that for now come in two pieces that are bolted together.

This different tire, it seems, mounts to this different wheel in a singularly odd fashion. Instead of the bead tucking under the edge of the rim as you're accustomed to seeing, the bead actually runs right on the edge&emdash;even slightly outside of the rim, producing a hard rubber "lip" all the way around the circumference.

It is this mounting structure, says Michelin, that makes its new PAV concept so special. PAV&emdash;French for Pneu Accrochage Vertical, or Vertically Attached Tire&emdash;is being positioned as an entirely new and revolutionary tire technology.

The mounting process, immediately visible, is of course the first difference. Because the bead of the tire rests right on the edge of the rim, says Michelin, it's not nearly as likely to peel off in hard cornering or under low-pressure conditions. Whereas regular wheels, when pushed from underneath or behind, tend to come off the rim because they're attached horizontally, PAV's vertical attachment actually becomes stronger, the bead of the tire pressing even more firmly into the rim.

Another key benefit of PAV technology is its modularity. Mixing and matching features is easy, because the insides of PAV rims are designed to accept a variety of other features. One option that is sure to be important is a hard rubber insert that gives the tire extended mobility characteristics. In the event of a deflation, the car can still ride on this rubber insert&emdash;it's as if a second tire has been mounted within the first. There's also room on the rim for a pressure-monitoring system that helps the driver not only maintain correct tire pressures for fuel economy reasons, but also serves to warn the driver in the event of a sudden deflation.

The rim itself, with its asymmetrical design, further helps to hold the wheel in place&emdash;if it does peel off one side, it is prevented from peeling off the other. This asymmetrical design also helps to make mounting the tires easier, reducing mounting pressures and requiring far less effort than conventional tire designs.

Out on the track, the benefits of PAV are immediately obvious. The coke-bottle shape, strange-looking as it is, combined with the vertical attachment, greatly increases the tires' sidewall stiffness; handling is both objectively and subjectively head and shoulders above any conventional tires. Cars equipped with PAVs have more eager turn-in, better steering feel, and display far less of a tendency to slide. Grip is perceptively higher. (The tires are so good, in fact, that on a lap in a car equipped with normal tires after experiencing them, I took a corner at a speed that felt fine in the PAVs and almost spun the car.)

In the wet, their performance advantage is even clearer. In a Honda Accord equipped with standard tires, I was slipping and sliding all over Michelin's wet handling course. Using PAVs of the same size, same tread pattern and rubber compound, I was able to navigate the course not only without skidding or losing traction, but was also able to do it perceptively faster.

When deflated, the PAVs remain manageable though noisy. As with all extended mobility tires, they pull slightly to the side of the deflation if you remove your hands from the steering wheel, an effect that is more pronounced when one of the drive wheels is deflated. Nevertheless, the effect is not overpowering, and driving the car at normal speeds up to 100 km/h remains easy. The noise that they make, though, is perceptibly louder than other extended-mobility tires that I've driven, something that I, and most of the other journalists I talked to, considered a plus. The sound is particularly evident under acceleration and hard braking, though the low-pitched fluttering is noticeable at any speed.

Good as it is, PAV is still a technology that is very much in its infancy. The tires that we were testing were a few of just a handful of tires coming off an experimental production line. As such, their ride comfort and noise quality weren't up to Michelin's usually high standards. On a simulated highway at the far end of the test track, their sound, a loud but low-pitched droning, was particularly noticeable. They also had cost several hundred dollars a piece, not to mention the not-insignificant cost of the modular Gotti alloy wheels on which they were mounted.

There's also the hurdle of weight to consider. A set of four PAV tires is more than ten kilograms heavier, on average, than a set of five conventional tires (including a spare), something that negates the fuel savings imparted by their low rolling resistance. To be honest, I didn't much notice the extra weight, and the handling advantages of the tire make up for it in my mind; however, it's an area that certainly needs to be addressed before the tires hit the shelves.

Right now the biggest obstacle for PAV is getting it into the marketplace. While Michelin expects that the tires will be street-legal by the end of the year (our driving experiences were conducted on a test track,) the amount of rework that they will mean for car manufacturers has yet to be seen. No manufacturer will be willing to design a car around a tire and wheel combination that is only available from one manufacturer.

To that effect, Michelin is in active negotiations with several of its partners and competitors to license the technology, and is also in discussions with several OEM manufacturers. They're working with engineers, of course, but they're also working with stylists, trying to find a way around the ungainly sidewall shape, or, at least, to use it creatively. (One advantage that PAV's asymmetrical rims give is the possibility of a much lower aspect ratio, something that car designers love.)

So far, no news of PAV being used by other companies has surfaced, though Michelin hints that you'll see the first OEM applications at the end of 1998 and the beginning of 1999, with wide acceptance of the technology in the 2003-2005 area. By then, the tires should be available from a number of manufacturers, and there will be some aftermarket-wheel activity.

What is clear is that PAV is a major paradigm shift in tires, something that now, having seen it, will have thousands of people muttering to themselves, "why didn't I think of that?" Despite the obstacles that the technology still faces, I have the utmost confidence that the car I'll be driving around twenty years from now&emdash;whether or not it's shod with Michelins&emdash;will have coke-bottle sidewalls and a weird lip around the rim.

 

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