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Ford Motor Company Root Cause Investigation Continues

20 December 2000

Ford Motor Company Root Cause Investigation Continues

    DEARBORN, Mich., Dec. 19 The following is a statement from
Ford Motor Company :

    The engineers and scientists of Ford Motor Company continue to meet with
both the National Highway Traffic Safety Administration and Firestone on a
regular basis to discuss our ongoing investigation of the Firestone tire
recall.  Our ongoing statistical analysis and test data seem in agreement with
many of the preliminary conclusions of Firestone, as we understand them.

    *  Our testing on Ford and other makes of vehicles and on tire test rigs
show that P235/75R15 ATX and Wilderness AT tires do run hotter than similar
competitive designs, although we do not know what aspects of the design cause
this.
    *  Our test data also show that rubber cohesion is lower in the belt area
of Decatur-built tires.  The test data, however, do not tell us what aspect of
the manufacturing process may cause this.
    *  We have not tested or analyzed tires that have had a puncture repaired,
but it seems reasonable that a tire that is already sensitive to heat because
of design and manufacturing aspects could be progressively damaged if it was
run hot because of lower inflation pressures prior to or after a repair.
    *  The weight of the Explorer is well within the load rating of the tires.
The curb weight of the heaviest four-door 4x4 model of Explorer increased only
154 pounds from 1991 to 1997.  Our experience with more than 2.9 million
competitive make tires that performed almost flawlessly in the field leads us
to conclude that the vehicle is not a significant contributor to tread
separation.
    *  Firestone's data show that the somewhat higher occurrence of claims for
tread separations on a vehicle's left rear tire happens on a majority of light
trucks and SUVs from most manufacturers.  The difference in weight, rear left
to right, on the Explorer is less than 100 pounds.  Our analysis indicates
this left-to-right rear weight distribution on the Explorer is not
significantly different than on similar competitive vehicles.
    *  Independent real world accident data continue to show that the Explorer
is among the safest vehicles in its class for all serious injury accidents, as
well as for rollover accidents.

    While Ford's investigation continues into the cause of Firestone tire
tread separations, our preliminary root cause hypothesis is: The design of the
tire generates high stresses and heat in the wedge and belt area.
Manufacturing processes at Firestone's Decatur Plant reduce the cohesion level
of the rubber in that same area of the tire.  This reduced strength permits
cracks to propagate between the steel belts.  We believe it is a combination
of manufacturing factors and the reaction of the tire design to field
operating conditions including hot weather and very low tire pressure, that
have caused the increased failure rate of these tires.
    The important thing for our customers is that these elevated rates of
tread separation not occur again.  Ford Motor Company already is using what it
has learned to enable early identification of problems at the time tires are
produced and when they reach customers.