No tire, regardless of its quality, is indestructible.
Certain conditions of use and abuse can stress a tire
beyond reasonable operating limits, causing it to come
out of service even when considerable tread remains.
Such conditions are clearly indicated by the damage they
leave on the tire itself. Listed below are some common
damages and the signs they leave behind. Please
understand that this list is by no means exhaustive
and is intended only as a general guide.
UNDERINFLATION
This condition is often referred to as a “run-flat” tire.
It is caused by operating a tire at very low or zero
pressure. When a tire is run at normal highway speeds,
underinflated, it flexes too much and builds up heat.
This heat damages the inner liner, casing, and outer
sidewall of the tire. If not remedied quickly, the tire will
be irreparably damaged.
In extreme cases, the sidewall of the tire is destroyed,
from the excessive heat and the weight of the vehicle
crushing/cutting the tire against the wheel as it rolls on
the uninflated sidewall. According to guidelines put out
by the Rubber Manufacturers Association (RMA), any tire
that has been run at less than 80% of normal
recommended pressure for the load it is carrying should
be inspected for possible damage.
When one tire in a dual configuration comes out of
service due to under-inflation/run-flat damage, the
other tire in the dual configuration should be inspected
immediately. If the unserviceable tire was underinflated,
that means the serviceable tire was carrying more and
more of the load for that wheel position. Consequently,
it too may have suffered some casing damage.
FATIGUE RUPTURE
This type of damage is sometimes called a “zipper rip”
because of the zipper-like effect it creates in the steel
casing cords of the damaged tire. When a casing cord is
damaged or repeatedly and excessively bent due to over-
load and/or underinflation, it will eventually break and
subject the cords on either side to even more stress.
When enough strength has been lost due to additional
cord breakage, a rupture occurs and can progress rapidly
along the path of least resistance in the upper sidewall.
This can happen hours, days, or even months after the
initial damage event when all evidence or memory of the
initial damage or overload/underinflation is gone.
Casing cords in the MICHELIN
®
truck tires used on
motorhomes are very strong twisted steel cables.
Extreme over-deflection of a tire, that can occur during
improper blocking of tires or high energy impacts, may
weaken the structure of the cable so as to make it less
tolerant of the repeated bending stress encountered in
normal use. If in addition, the integrity of the steel cords
is degraded by corrosion from moisture reaching the
cords through cuts or tears in the rubber, their tolerance
of these conditions will be even further reduced. This
corrosion may result from mounting damage, foreign
objects left inside the tire, road hazards, tire
mishandling, or even improper repair of a nail hole.
DUAL KISSING
While somewhat romantic in name only, this type of
damage refers to what happens when two tires in dual
configuration make contact with each other while in
operation. The heat generated by the friction between
the two tires severely weakens the casing material of the
dual tires. This is easily seen on the sidewalls of the tires
where the duals came in contact. The condition may be
caused by several factors:
- improper mounting
- incorrect wheel width or offset
- underinflation
- “casing growth”
In this last case, the fabric casing cords of the tire
actually stretch and expand, causing the tire to touch
or kiss, under load at the contact patch.
8
MICHELIN
®
RV Tires
Underinflation
Fatigue Rupture or “Zipper”
COMMON TIRE DAMAGES
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