CapriRacer wrote:
Don,
3 thoughts:
1) Included on my web page is an analysis of the pressure spec. Short version: The vehicle's tire pressure spec did not result in an overloaded tire.
This is from Dr. Govindjee report on page 34. Seems to contradict you statement as to the affect of pressure and heat on a tire.
5.3 Thermal demands
The climate related degradation of properties that was seen in the return
tire survey points to the importance temperature plays in material behavior.
Likewise, aging studies on ideal laboratory specimens show a measurable
effect of thermal and oxidative aging. There are two major contributors to
the temperature of the tire: (1) is the ambient temperature and (2) is the
heat generation from within the tire.
1. Low inflation pressure, highway speeds, and heavy cargo loads all play
a negative role in terms of contributing to thermal aging. When all
three factors are present, the temperature rise in the belt region of the
tire can be as high as 50C over the ambient temperature.
2. When carrying heavy loads and at high speeds, decreased inflation
pressure can substantially increase tire temperature.
2) Firestone's own consultant (Dr. Govindjee) identified the problem in the tire.
I could not find where he said the tire was defective however there were higher failure rates between Firestone's two factories.
5 Conclusions
This study has found no single causative agent for the tire failures. It has
found a number of comparative differences in tire models that are likely
related to the tire failures and these are summarized below. The primary
issue that impedes additional progress is the lack of established criteria for
different types of tire failures. Development of such criteria is only today
becoming scientifically and technologically possible.
The other main point is why were no other vehicles seeing the same failure rates using the same tires that Ford was having with the Explorers? These tires were also being used on the Ford Ranger without any issues. The other thing pointing to low tire pressure and heat is that the vast majority of the tire failures were happen in hot climates.
3) The tire was recalled, but the vehicle wasn't. If the Feds didn't think the tire was the sole problem, why didn't they recall the vehicle?
The vehicles were recalled Ford had to replace those tires not Firestone. The vehicle manufacture is responsible ALL parts installed on their vehicles not the supplier. The total cost to Ford for the recall was over 3 billion dollars.
Barry
