Here's the link to actual NHTSA Tire Advisory of June 2008.
http://www.nhtsa.dot.gov/portal/site/nhtsa/template.MAXIMIZE/menuitem.f2217bee37fb302f6d7c121046108a0c/?javax.portlet.tpst=1e51531b2220b0f8ea14201046108a0c_ws_MX&javax.portlet.prp_1e51531b2220b0f8ea14201046108a0c_viewID=detail_view&itemID=be9d195e85a3a110VgnVCM1000002fd17898RCRD&pressReleaseYearSelect=2008The items cited in that advisory are shown in
italized type below. Highlighted (
Bold) is my own.
The risk of a serious crash during hot weather can be heightened
by tires that are worn out, under-inflated or too old, ...
NHTSA research shows that hot weather – and overloaded vehicles –
can add significant stress to a tire, especially if it is not
properly inflated. Old tires also are subject to greater stress,
which increases the likelihood of catastrophic failure.Note that overloaded or underinflated tires add significantly to
greater tire temperatures... adding to the climate condition, or
even over-riding climate (ambiant and road surface temperatures).
Both overloading and underinflation dramatically increase the
stress on the tires structure. The greater the mileage on
overloaded or underinflated tires the greater their internal
temperature and greater their accumulated stress (cyclic fatigue)....
hence the faster they "age". Data collected on vehicle accidents
attributed to tire failure would have to determine the history of
underinflation, overloading instances, and miles driven at known
speeds under those conditions to differentiate pure relation of age
with relation to use induced failure mechanism. Unfortunately this
data is largly unavailable after the fact when an accident has
occured. It therefore appears to me that the age factor
relationship is largly anecdotal as primary causes.
I also pointed out in my prior post on this topic (and related NHTSA
link to data) that the accelated stress & aging evalutions showed
far greater variation by tire brand and model and that mileage and
age couldn't be differentiated. I'm not disputing that age of the
tire alone isn't a factor... only that it's relative significance
in tire related accidents is far, far behind history of tire use
conditions and mfg'ing variations (internal defects). I'm also
guessing that tire mfg'er recommendations on maximum load ratings
may be driven largly by the target client vehicles loads ... i.e.
perhaps Ford Explorer's mfg'ers desired max load is X, so the
competing tire mfg'ers would tend to bias their tests to
be "acceptable" under load X as "max" load. This would also have
something to do with OEM vehicle's tire price contracts. Just my
opinion.
...
tire condition is important for all vehicles, it is especially
critical for those more prone to rollover when tires fail. That
would include sport utility vehicles (SUVs), pickups or other
vehicles with a higher center of gravity.I can't find the report now, but while researching this last week, the tire related failures in US were ranked as:
1 - Southwestern States, Pickups
2 - Midwestern States, Pickups
So it turns out that hottest climates with high proportion of
Pickups (assumedly with higher proportion used in farm &/or hauling
applications) are the dominant vehicles with tire caused
accidents. That's consistant with both tendency for tires to
often be "overloaded" during their use period, high center of
gravity (especially when overloaded), and longevity of use
independant of mileage. I wonder how many of these failures are for
rear tire catastrophic failures?
...
check tire inflation with an inexpensive gauge, using the
vehicle manufacturers’ recommended pressures, which are found on
the driver’s side door pillar or in the owner’s manual. Some tire and vehicle manufacturers have issued recommendations
for replacing tires that range from six to ten years of age.
Consumers are advised to check with their tire or vehicle
manufacturer for specific guidance.
“Remember that it is vitally important to check your spare tire
too,” said Administrator Nason. “Your spare can be a real safety
hazard if it is old or under-inflated.”