The Width (205)
The width of the tire, from sidewall to sidewall, in millimeters. A 205
is 205 millimeters, or 20.5 centimeters, wide. The tread width is
actually somewhat smaller than the tire's actual width. When referring
to the width of a tyre most people will assume that it is simply the
measurement from one side of the tyre to the other. There are however
four different width measurements which can be applied to a tyre:
-
Overall width
-
Section width
-
Tread width
-
Loaded width
Overall width of a tyre is the measurement from side to side including
any additional sidewall items such as kerbing ribs, raised letters etc.
This is important, particularly when upgrading tyre size, as different
manufacturers tyres may have different overall widths even though the
tyre size is the same.
Section width is the measurement of the tyre from side to side excluding
any additional sidewall items such as kerbing ribs, raised letters etc.
Tread width is the portion of the tyres width that is covered by a tread pattern.
Loaded width is the same measurement as the overall width but taken when the tyre has the relevant load applied to it.
The Profile Or Aspect Ratio (55)
This is the sidewall's height from the inside diameter to the outside
diameter. It is expressed as a percentage of the width. A 205/55 is 55
percent as tall as it is wide, As aspect ratios decrease, the tire's
firmness increases. Smaller aspect ratios, such as 35 or 40 are
generally reserved for performance tires on sports cars.
R
The tire's type of construction. R stands for Radial, and all new cars
and light trucks today use radials. You may also see B in this spot for
Bias Ply. Bias ply tires were used prior to the mid 1970s.
Rim Diameter (16)
The tire's inner diameter, which matches the outer diameter of your car's wheels.
Speed Rating (W)
All passenger tires have a speed rating expressed as a letter. Those
letters and the corresponding speeds the tires are capable of are
included in this chart:
S: 112 mph
T: 118 mph
U: 124 mph
H: 130 mph
V: 149 mph
W: 168 mph
Y: 186 mph
Z: over 186 mph
A Speed Rating is really an indication of a tire's ability to dissipate
heat to avoid a blowout. Higher speeds mean greater heat buildup. Tires
with higher speed ratings are constructed to handle heat better. In
general, they also ride harder than tires with lower speed ratings. S-,
T-, and U-rated tires are considered regular passenger-car tires. H- and
V-ratings are reserved for touring tires, which are generally found on
sport sedans. The Z rating is for performance tires found on sports
cars.
Load Rating (91)
Load ratings range from 0 to 279 and each has a corresponding weight
associated with it. A 93 load rating means that tire is certified to
carry up to 1433 pounds at maximum inflation pressure. If a car weighs
4000 pounds, then each tire handles 1000 pounds with no passengers or
cargo aboard. If you intend to tow a heavy boat or trailer, you should
buy tires with a higher load rating. This will require some math to
figure out the vehicle weight, the trailer weight, and the weight of a
load you may carry inside the vehicle while towing. Add it all up,
divide by four, and make sure your replacement tires have a
corresponding load rating.
Leslie