Just to stir the tire pot....

[David Brady]

Folks,

With permission from Neil, I'm cross posting this post Neil
wrote for the DieselRvs group:

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-----Original Message-----
From: Neil & Pat [mailto:undoone@...]
Sent: Tuesday, July 18, 2006 8:43 AM
To: Diesel-RVs@yahoogroups.com
Subject: RE: [Diesel-RVs] Tires



For all of those following this very important forum thread re: tire ageing
I offer the following from the perspective of a 36 year tire design/product
support engineer, an RV Safety author and a 32 year active RVer.

Tires are made primarily of rubber, and we intuitively know rubber ages and
deteriorates over time. It follows that TIRES DO NOT LAST FOREVER! The life
expectancy of a tire in RV service is not easily predicted. In this case we
are speaking of the casing life as opposed to the tread life. The difficulty
of this is that the life of a tire carcass depends to a great degree on how
the tires are utilized and maintained. For instance, a tire exposed to the
rays of the sun for extended periods of time, or stored in the presence of
high levels of ozone, may have a relatively short life. Similarly, a tire
operated near, at, or over its rating may also have a relatively short life.
Recalling that under-inflation is the same as overloading, poor maintenance
practices will also adversely affect the tire life.

Rubber products are cured during the manufacturing process using a process
called "vulcanization", this process is promoted by both a chemical reaction
and heat. During this process the rubber changes state from a tacky soft
material to the pliable yet strong material we are used to seeing in our
tires. When the tires are removed from the heat and mold the chemical
action continues; therefore, the curing continues throughout the life of the
tire. This accounts for some of the ongoing deterioration we observe in our
RV tires.

In fact tires operated on a regular basis will generally enjoy a longer
carcass life then tires which sit statically for a high percentage of the
time. This is because tires contain compounds that keep the rubber supple -
tire flexing and internal heat activates these compounds. If the tire is not
used regularly (flexed), it dries out quickly! Visit an automobile museum to
see this principle in action. Many of the automobiles there were restored
using new tires. After several years in a fully protected environment the
tires are deteriorated and cracked. The infrequent usage of RV's somewhat
parallels this action.

RVers commonly use chemicals to polish the sidewall of tires to enhance
their appearance. Often this causes or accelerates damage because of harmful
components contained in the "tire dressing." The tire manufacturers suggest
using nothing but mild soap and water .. (They go on to specifically state)
that product(s) that contains petroleum products, silicon or alcohol should
not be used." ... Even with an acceptable "tire dressing" you may be wasting
your time and money because you cannot coat all areas of the tires inside,
outside and in the tread grooves that are acted on by ozone and ultraviolet.
Meanwhile, the vulcanization process continues.

...storing our RVs for long periods...hurts tires two ways: first, the tire
is not flexed regularly activating the chemicals in the rubber placed there
to retard deterioration; and second, we often park our RVs on ...asphalt or
concrete. These materials will leech those same chemicals from the tires
with the effect of shortening its life. (Use a barrier or wood or plastic.)

So how long will a tire last?...most tire manufacturers agree that five to
seven years of age is the norm for RV service ...should (you) panic and
immediately throw away your tires when they reach the five year age? No.
What a knowledgeable RVer should do at this point is to become more diligent
and watchful of the tires on his/her RV. That means that you should be
especially observant of the sidewall (both sides) looking for deterioration
or cracks, which might expose the carcass material (cords) to the
atmosphere. Do not forget the bottom of the tread grooves, and look for
blisters or bulging on the sidewalls, watch air pressure closely because an
unexplained or recurring air pressure loss could be deterioration of the
inner liner of the tire.

If any tires fails ... (or) when any of these signs of deterioration begin
to show, that is the time to go shopping (to replaces all tires of the same
age). Hopefully, this pro-active approach will afford you the opportunity to
shop for tires in a more convenient manner and avoid the very costly and
dangerous potential of failing tires on at a time while on the road.

Neil LeKander