|
|
'65-'66
MUSTANGS |
|
Wheel |
Backspace |
Tire
Size |
|
15x6 |
4.000 |
P215/70R15 |
|
15x7 |
4.250 |
P225/60R15 |
|
15x8 |
4.500 |
P235/60R15 |
|
16x7 |
4.250 |
P225/60R16 |
|
16x8 |
4.500 |
P225/50R16 |
|
17x7 |
4.250 |
P205/50R17 |
|
17x8 |
4.500 |
P235/45R17 |
|
'67-'70
MUSTANGS |
|
Wheel |
Backspace |
Tire
Size |
|
15x6 |
4.000 |
P215/70R15 |
|
15x7 |
4.250 |
P225/60R15 |
|
15x8 |
4.500 |
P225/60R15 |
|
15x9 |
5.500 |
P235/60R15
('69-'70
only)
|
|
16x7 |
4.250 |
P205/55R16 |
|
16x8 |
4.500 |
P255/50R16 |
|
17x7 |
4.250 |
P205/50R17
|
|
17x8 |
4.500 |
P235/45R17 |
|
17x9 |
5.500 |
P245/40R17
(P275/40R17rear
axle)
|
|
18x10 |
6.500 |
P225/40R18 |
|
20x10 |
5.000/custom
|
P225/35R20
(rear
axle
only) |
Why Nitrogen
in Tires?
Craig
Knarich of
Pit Crew
Tire Service
explained to
us that
since
nitrogen is
denser than
oxygen, the
larger
molecules
escape less
easily from
tires,
resulting in
a more
gradual loss
of pressure
over time.
Research
shows that a
tire
inflated
with
nitrogen
loses its
pressure
three times
slower than
if it were
inflated
with air. As
a rough rule
of thumb, if
your tire
pressure is
20 percent
below the
optimum,
you'll
reduce tire
life by up
to 50
percent and
the
additional
rolling
resistance
can add 10
percent or
more to your
fuel
consumption.
Across the
life of a
tire, that's
a big
financial
penalty. The
Department
of Energy
reports that
4,000,000
gallons of
gasoline are
unnecessarily
wasted every
day due to
low tire
pressure.
Nitrogen is
also
moisture-free,
so pure
nitrogen-inflated
tires
experience
less
steel-belt
and rubber
degradation,
resulting in
longer tire
life. The
use of
nitrogen
also reduces
valve and
wheel
corrosion.
Nitrogen-inflated
tires also
run cooler
and require
less
maintenance,
according to
a Goodyear
application
bulletin.
Non-flammable
nitrogen
technology
has been
used in
race-car
tires for
over 30
years.
Decoding
Tire Codes
The series
of letters
and numbers
on a tire's
sidewall
tell a lot
about what
you're
getting for
your money
as well as
the tire's
capabilities.
The first
series of
numbers
denotes tire
size. After
that, the
two most
important
things to
look for are
the service
description
and the
uniform
tire-quality
grade or
UTQG.
Using the
information
in the
service
description,
we know that
a set of our
P215/60R16-94T
tires will
carry a load
of 5,908
pounds at up
to 118 mph
safely.
While the
load range
is fine for
our '67
Mustang, the
118 top
speed could
easily be
exceeded,
calling for
a tire with
a higher
speed
rating. We
should note
that the
speed rating
doesn't
apply to
tires that
are worn
out,
repaired,
damaged,
retreaded,
or not
properly
inflated.
|
LOAD
INDEX |
CAPACITY
(IN
LBS) |
|
71 |
761 |
|
72 |
783 |
|
73 |
805 |
|
74 |
827 |
|
75 |
853 |
|
76 |
882 |
|
77 |
908 |
|
78 |
937 |
|
79 |
963 |
|
80 |
992 |
|
81 |
1,019 |
|
82 |
1,047 |
|
83 |
1,074 |
|
84 |
1,102 |
|
85 |
1,135 |
|
86 |
1,168 |
|
87 |
1,201 |
|
88 |
1,235 |
|
89 |
1,279 |
|
90 |
1,323 |
|
91 |
1,356 |
|
92 |
1,389 |
|
93 |
1,433 |
|
94 |
1,477 |
|
95 |
1,521 |
|
96 |
1,565 |
|
97 |
1,609 |
|
98 |
1,653 |
|
99 |
1,709 |
|
100 |
1,764 |
|
101 |
1,819 |
|
102 |
1,874 |
|
103 |
1,923 |
|
104 |
1,984 |
|
105 |
2,039 |
|
106 |
2,094 |
|
107 |
2,149 |
|
108 |
2,205 |
|
109 |
2,271 |
|
110 |
2,337 |
The second
half of the
service
description
is known as
the speed
rating.
Devised to
give the
buyer an
awareness of
the tire
capability
for safe
operating
speed, it is
the T in the
94T service
description.
Three of the
most common
speed
ratings are
S, H, and V.
The complete
speed-rating
table is as
follows.
|
SPEED
RATING |
MAX
MPH |
|
M |
81 |
|
N |
87 |
|
P |
93 |
|
Q |
99 |
|
R |
106 |
|
S |
112 |
|
T |
118 |
|
U |
124 |
|
H |
130 |
|
V (VR) |
149 |
|
W (ZR) |
168 |
|
Y(ZR) |
186 |
|
|
Many wheels, both factory and aftermarket, are not centered using the central wheel opening. Rather, the wheel is centered on the bolt pattern for optimum balance when installed onto the car. This is called being lug-centric. The problem is that many tire stores just use a cone and don't have the lug-plate fixtures shown here, which are used to center the wheel perfectly on the tire-balancing machine. If you're having trouble balancing your styled-steel wheels or Magnum 500s, check to see if your balance shop is using the correct centering fixture.
|
This is our project's Wheel Vintiques wheel and Nitto tire mounted on the Hunter Road Force spin-balance machine inside Pit Crew's mobile tire truck. This state-of-the-art balancer even simulates the vehicle load using pressure from a roller. This replicates actual operating conditions for the most accurate balance possible. Notice the lug-plate in use on the wheel, too.
|
While the wheel and tire assembly turn on the balancer, information regarding the state of balance is reported on the computer screen using Hunter's SmartWeight system. The machine then instructs the operator where to place the weights and describes how heavy they should be in order to correct the imbalance completely.
|
With most aftermarket wheels, there is no provision for balance weight attachment as there is on factory wheels. The solution is these self-adhesive lead weights that can be applied to the wheel without damaging the polished or chromed surface. They are available in exacting increments down to 11/44 ounce, or 7 grams. The higher-quality weights shown in grams are much more accurate than the "chocolate bar" weight at the top of the photo. Craig Knarich of Pit Crew Tire also stressed the use of the proper lug nut for the wheel being used. He said aftermarket wheels often come with the wrong lug nuts and can cause vibration issues.
|
Let's look at a tire sized at P215/60R16-94T. This is an average tire size you might consider for a '67 Mustang. The first number, 215, is the tread width in millimeters. The next number, 60, is called the aspect ratio. Here, sidewall height is expressed as a percentage of tread width. In this case, it's 60 percent, or slightly more than half the width of the tread. The R16 tells you that it's a radial tire made to fit a wheel 16 inches in diameter. Understanding the tire size code will enable you to purchase exactly the right sized tire for your needs.
|
The federal government requires tire manufacturers to grade tires in three areas. Known as the Uniform Tire Quality Grading System, it provides guidelines for making relative comparisons when purchasing new tires or evaluating tires put on new vehicles. This is helpful, but it is not a guarantee of how a tire will perform or how long it will last because many factors have a significant influence on tire performance and longevity. First, the tread wear grade gives an indication of a tire's relative wear rate. The higher the tread wear number, the longer it should take for the tread to wear down. For example, a tire grade of 400 should wear twice as long as a tire grade of 200. Second is the traction grade, which is an indication of a tire's ability to stop on wet pavement. A higher grade means a shorter stopping distance. Traction is graded from highest to lowest as "AA", "A", "B", and "C". Third are the temperature grades, which are an indication of a tire's resistance to sustained heat From highest to lowest, a tire's resistance to heat is graded as "A," "B," or "C."
|
While
the
first
series
of
numbers
describe
the tire
size
exactly,
the last
portion
of the
code,
which is
94T, is
known as
the
service
description.
It is
divided
into two
parts,
the load
index
and the
speed
rating.
The load
index
for cars
and
light
trucks
ranges
from 70
to 110.
The load
index
table is
shown
below.
Capacities
listed
are for
a tire
that is
properly
inflated.
An
alignment
should
be
considered
mandatory
on
any
new
wheel
and
tire
purchase.
We
have
seen
an
improperly
aligned
car
completely
ruin
a
set
of
new
tires
within
500
miles.
Many
tire
shops
include
an
alignment
with
a
new
tire
purchase,
so
shop
around.
|
