Most Emergency Vehicles Have Unsafe Low Tire Pressure In Test
A recent survey was conducted of tire
pressure on the dual tire assemblies of emergency medical service
vehicles. Here's what was found:
About 39 percent of the tires couldn’t be checked at all,
because valve stems were inaccessible. We don’t know if inflation
was correct or not. Worse, even if one of these tires needed air,
there was no way to add any.
Some vehicles had extension hoses, so at least we could check
them. Nevertheless, results were pretty grim.
Nearly two-thirds of those tires were underinflated by at least
20 psi. That’s dangerously low. Since the manufacturer’s
specification is 80 psi, these tires were 25 percent underinflated.
The tire industry considers any tire that's been run on the
road 20 percent or more underinflated to be “run flat.”
Running flat can result in very serious damage to the tire that
can cause it to fail catastrophically – and without warning.
Of these underinflated tires, 2/3rds were the inside tire of
the dual assembly, which is nearly impossible to see. Only about
13 percent – roughly one in eight of the tires we checked
– had the correct inflation pressure.
The tire industry considers any tire that's
been running on the road while it's been underinflated by more
than 20% to be a “run flat tire.”
So where does the air go?
Why can’t we just put air in
our tires once, then forget about them? How does the air escape?
Well, air can escape from tires in lots of ways. Clearly, there could be a puncture, a nail that’s causing “a slow leak.” But there are lots of other
ways air can escape.
Today’s tires are tubeless, which means that the tire
itself has to seal directly against the wheel.
Improper or inadequate lubrication or a damaged wheel can cause air to
escape at the interface between tire and wheel. Damaged, defective
or contaminated valve stems, as we’ve seen, can leak
as well.
But even if all those things were perfect, tires would still
lose air. Depending on size, they can lose between 1 and 2
psi per month.
How is it getting out? Well, just as gases can permeate the
membranes of the body, air can and does permeate the rubber
in tires. Air molecules literally find their way out of the
tire – slowly – resulting in a gradual loss of air
pressure.
That's why you need to check your tires frequently, even if
there’s no obvious damage to them.
Just as gases can permeate membranes
in the human body, air can permeate the rubber in tires, resulting
in a loss of air pressure of between 1 and 2 psi per month,
depending on the size of the tire.
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