|
Article (7) Tire Pressure Can Be A Killer
by Rod Jones
There’s a story about a person (you decide if it
was a man or woman, bald, blond or brunette) who went to a hardware
store, looking for a stick of dynamite. The clerk told the
person he didn’t have any dynamite, and then, out of curiosity, asked
why the person needed dynamite. The person responded it was for
a Roadside Emergency Kit in case the car has a flat. "In case
the car has a flat?" asked the clerk. "Sure," the person said, "so I
can blow up the tire." Flat tires are bad news—especially on a
motorcycle and especially when the flat happens all at once from a
blowout. The result is devastating and potentially lethal, as
graphically illustrated a few weeks ago in our own Gator Service Shop.
Mike, one of the mechanics, brought out a tire from a badly damaged
motorcycle. The tire was split open and looked like a small
explosive device had gone off inside. In effect, that was
exactly what had happened. But in this case, it wasn’t dynamite,
C4, or any other explosive chemical, it was heat and pressure,
generated by a severely under inflated tire. Fortunately, no one
died. But how did under inflation lead to a blowout?
|
|
When a tire is under inflated, several things
happen. First of all, it is less rigid, which creates more
rolling friction and increased heat. Additionally, the sides of
the tire bend and flex too much. The flexing and bending
generates even more heat. This heat can exceed the ability of
the tire to dissipate it, especially on hot days, and can cause
serious damage to the tire, including tread separation and blowout.
Under inflation is dangerous for another reason, as
well. In the presence of water on the roadway, under inflation
can result in hydroplaning. Hydroplaning occurs when the water
pressure under the tread exceeds the air pressure inside the tire,
pushing the center of the tire off the road, and causing the tire to
become concave. When that happens, the tire essentially starts
to ride on the small stream of water underneath it.
Steering at that point is lost, as the tire goes in the direction the
stream of water takes it.
So how do our tires become under inflated?
Obviously, they could develop a slow leak from a puncture or a leaky
valve stem. But perfectly good tires lose air too, in fact as
much as one pound per square inch (psi) per month. Moreover, as
temperatures drop, perfectly good tires can lose one additional psi
for every 10-degree drop.
The solution to under inflation is simple—know the
correct tire pressure for our tires, check them on a regular basis,
and keep them properly inflated. Unfortunately, most of us do not
check our tire pressure as often as we should. When was the last
time you checked the pressures on your bike? If it was before
our cooler weather, it’s almost a certainty your tires are low—mine
were.
The key to proper inflation is developing a weekly
routine—a little time well invested. We need to keep in mind
that front and rear tire pressures may not be the same. On
dressers, for example, when there is a rider and a passenger, the
recommended pressure for the front tire is 36 psi, while the rear tire
is 40 psi.
So, where do we find the proper inflation numbers?
If we’re running stock tires, the recommended tire pressures are in
our Owner’s Manual. For other than stock tires, information
should be obtained from the tire manufacturer. (Note: The
pressure listed on the tire sidewall is a maximum that should
never be exceeded, but it may not be the recommended pressure.)
And remember, tires should be checked when they’re cold, that is after
they’ve set a couple hours, or only been used for a short trip to the
service station. Ride safe and have fun.
|