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.