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If there's one thing that both car and motorcycle drivers and
enthusiasts share when enjoying a nice drive down the coastline or a
winding backwoods trail, is the contact that is made between them and
the road. Tires are probably the single most important piece of
equipment found on today's roads. Not only are tires the only things
that touch the asphalt when you ride, but they account for much of
the safety issues in keeping road travelers away from harm and injury.
The relationship between rider and tire is much more important
than many riders realize. In today's fast-paced technologically
advancing society with engines and vehicles being built stronger,
bigger, and faster, tires play an even larger role. To help you get
better acquainted with today's tire technology and specs, let's take
a closer look at what comprises the make-up of the tire and what all
of the letters and numbers mean on the sidewall of the tire.
First off, there are 6 parts or sections of a typical motorcycle
tire that when constructed make it complete:
Tread - The tread is the outermost part of the tire made from
vulcanized rubber and is what riders are most familiar with seeing.
This surface or tread is what makes actual contact with the road, so
it's essential that the tread have a particular pattern with grooves
or sipes, which help channel water away from the contact patch.
Carcass - Otherwise known as the inside of the tire when it is
not mounted on the wheel. Consisting of overlapping synthetic cords
also referred to as plies, the carcass's build will ultimately
dictate the tire's strength, resiliency, and flexibility on the road.
Bead - The bead of a tire is the inner lip or edge that touches
the rim or wheel. Made from high-tensile strength steel wires, the
bead sits snuggly along the rim to form an airtight seal. Without the
bead, air would not be able to stay inside the tire.
Tube - The tube is located inside the circumference of a tire and
although most tires today are tube-less, they are still being used
specifically with motorcycles with spoked wheels. This is to prevent
air from leaking out around the spokes.
Sidewall - Another critical area of a tire is the sidewall
located between the tire's bead and the tread. It's important because
it needs to be soft enough to handle the road's bumps and potholes
yet tough enough to handle the rolling resistance when turning or
leaning into a turn. The other important feature of the sidewall is
that it specifies the tires characteristics, which are all of those
letter and numbers on the side.
Ply - These are the layers immediately underneath the tread layer
on bias-ply tires (versus radial) and are sections of plies that run
diagonally from one bead to the other with alternating plies going in
opposite directions.
Lastly, the numbers and letters designated on the side of each
and every tire have a specific meaning. Take this for example, 160/90
V# 15, which would be located along the sidewall section. This
seemingly innocuous data contains important information. The 160
number is the cross-section width of the tire in millimeters. You can
convert it to inches by dividing it by 25.4, as there are 25.4mm in 1
inch (for this example, 160mm divided by 25.4=6.299inches).
Next you will see the 90, which is the aspect ratio or the ratio
between the tire's height to the width. So the 90 means that the
tire's height from bead to contact patch (from both top and bottom
portions of the tire) is 90% of the tire's tread width. The V
illustrates the tire's speed rating or resistance to heat and speed,
and specifies the maximum speed a tire can safely withstand. The last
number is the diameter of the rim or wheel that this specific tire
should be mounted on. In this particular case, a 15-inch wheel.
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