Forget about flats
Is a run-flat tire in your automotive future? Goodyear and
Michelin are betting on it
Michelin and Goodyear are on a mission. They're both rushing to be
the Company That Let You Forget About Your Tires. While the wish may
sound farfetched&emdash;not to mention a little odd&emdash;the new
run-flat technology that both companies are introducing (Goodyear
calls it EMT, for Extended Mobility Tire, while Michelin calls it ZP,
for Zero Pressure,) make it not at all implausible.
The technology behind the tires&emdash;which on both sides amounts
to a proprietary compound inserted into a tire's sidewalls to stiffen
them in the event of a deflation&emdash;has actually been around for
a while. Racing tires have long had extended mobility technology;
more recently, Michelin (whose run-flats are an option on the Lincoln
Continental,) Bridgestone and Goodyear (whose EMTs were an option on
the 1994 Corvette) have sold run-flat technology.
In addition to the tires themselves, both manufacturers suggest
the installation of a pressure-monitoring device that warns you when
a tire is flat&emdash;for the Michelins, it's mandatory. For now,
each tire manufacturer has allied itself with one sensor
manufacturer, but they both expect that others will jump on the
bandwagon, promising lower prices.
What makes the tires that Michelin and Goodyear are bringing to
market so significant, though, is the fact that they aren't just
high-performance tires in small market segments. Michelin has already
been selling 60- and 65-series MXV4 ZPs in the States, and Goodyear
plans to offer EMTs in sizes that will cover 75% of the North
American market&emdash;even in 14-inch sizes.
How do the tires perform? It depends on what you expect, but the
short answer is flawlessly. Save for a slight listing to the side of
the punctured tire and a low fluttering noise, handling and ride are
unaffected; you can also nail the throttle through a corner and power
out of it as if nothing's wrong. In fact, one wonders if the tires
give enough audible and handling warning&emdash;some drivers might
just shrug off the beeping warning system as an electronic
malfunction, as the car still handles fine.
The effect's intensity varies from car to car and from tire to
tire. It's most pronounced in heavy front-drivers such as the
Oldsmobile Aurora, and much less noticeable on lighter cars and
rear-drivers. On both tires, there's none of the harsh ride that you
would associate with rock-solid sidewalls, inflated or flat. The
Goodyears are noisier in general than the Michelins, which pull to
the side a bit more.
What's most impressive is how driveable a car remains despite the
flat. A C5 Corvette on the Goodyears drove at 80 mph with ease, and a
one-hour highway cruise in a BMW 328i on the Michelins was equally
easy. Even when completely deflated, neither of the tires screech
more than normal, and they retain a smooth ride.
Track conditions being as they were at both companies' tracks, we
were unable to test the tires' wet performance when deflated. I would
expect a degradation of some sort&emdash;and one would be foolish to
drive aggressively in the wet given the audible warnings from both
the system and the tires.
For a premium of 10 to 25 percent over the price of a set of
normal tires, run-flat technology seems like a bona fide bargain,
even with the slight increase in rolling resistance and the marginal
weight gain (though, if you factor in removing the spare tire, as has
been done in the Corvette and the Prowler, this penalty is quickly
offset.) With highways that are a sea of flying truck tires, urban
roads that are intimidating after dark&emdash;not to mention those
light-brown trousers&emdash;run-flat tires allow you to get to a
service center at your convenience up to 50 miles away, without the
danger or annoyance that spares demand.
The only sticking point for now remains the warning system. While
both companies bandy about $50 as an ideal price, the two systems
that are currently approved run in the range of $500. And while it's
easy to add the system to a new car design while removing the spare
at a cost and weight savings, it's doubtful that many consumers would
want to ante up so much. Should its price come down, buying a set of
extended mobility tires will be a no-brainer.
Michelin's MXV4 ZP in 15- and 16-inch sizes will be available in
Canada on October 1st. Goodyear's EMT technology will be available on
a wide range of tires beginning in the first quarter of 1998.