by Hib Halverson
Recently the Idaho
Corvette Page (ICP) interviewed several engineers, brand managers and
public relations operatives at Goodyear. We learned a heck of a lot
general information about tires on Corvettes and other cars and light
We are going to start
with a sort of "Tire FAQ" we complied from the Goodyear
1) I should inflate my
tires according to the pressure indicated on the tire sidewall?
The handwriting’s not
on the wall–the tire sidewall, that is. The tire's maximum inflation
pressure not the vehicle manufacturer’s recommended pressure,
is molded on the sidewall. For normal operation, follow pressure
recommendations in the vehicle owner's manual or on the vehicle placard
located either in the glove box or on the driver’s door post.
The function of air in a
tire is to support the weight-carrying potential of a vehicle, according
to Goodyear tire engineers. Tires are built and rated to carry certain
load capacities. Automakers select tires compatible with the ride,
handling, traction, fuel economy and load requirements of their
vehicles. Vehicle manufacturers determine inflation pressures based on
2) A tread pattern is
needed to provide great traction on dry roads.
"slick", a tire without any tread, provides the
ultimate in dry traction due to the maximum amount of rubber in
contact with the road. A grooved tread pattern actually reduces
traction on dry roads but acts as a squeegee on wet roads to
remove water from under the tire and channel it through the
grooves and away for improved wet traction. That’s why the
Goodyear Aquatred III’s directional, "aquachannel"
tread design along with the similar design used by the Goodyear
Eagle GS-C and the Eagle F1 GS, grabbed so much attention when
it was introduced.
Goodyear F1 Supercar exposed. This is the tire on the
new Z06. It's Goodyear's newest performance tire and its
basic design features are typical of many of the
so-called "ultra-performance" tires. Image:
Black Dog Design/Chevrolet Communications.
3) If not for the
cost, race tires would be the ideal street tire for high-performance
Race tires are engineered
for specific track surfaces and race vehicle suspensions. On a
street-driven, high-performance car, race tires wear too quickly,
provide an uncomfortable ride and deliver poor handling on wet or icy
roadways. Rather than transferring race tire technology in total, in
many cases, certain technology used at the racetrack is engineered into
high-performance street tires. For example, ultra-high-performance
tires, such as Goodyear’s new Eagle F1 Supercar on the 2001 Z06es,
employ a stiffer carcass and aggressive tread compounds to provide the
performance attributes required for ultra high-performance vehicles.
4) Performance tires
wear out faster because of the sticky compounds.
Performance tires may
wear out faster than conventional family-car tires; however, tread
rubber polymers aren’t the culprits. In fact, new polymers and
ultra-tensile steel constructions are making performance tires last
longer than ever. Industry-wide, performance tires average about 45,000
miles in tread life, similar to the figures for tires used on ordinary
passenger cars. More often, rapid tire wear usually is due to powerful
vehicles and aggressive driving.
5) Wide tires provide
better traction under all weather conditions. Putting oversized snow
tires on a car delivers better snow traction.
In fact, the opposite is
true. Wide tires tend to "float" on deep snow and the tread
lugs never have a chance to "dig" through the snow to the road
surface to gain traction. Narrow tires are a better option in deep snow.
The tire acts similar to a knife cutting through butter; the blade works
best when using the narrow edge to push through the butter rather than
the wide flat side of the blade.
6) All-season tires
are so good that winter tires are unnecessary.
In some parts of the
country this may be true, but if you live in the northern-most states or
in Canada, the traction provided by winter tires can’t be beat. Winter
tires reign supreme in rural areas where snow remains on the road for
days. They provide 25 percent improved traction in deep snow over
all-season tires. Metal-studded tires deliver up to 40 percent greater
traction on hard-packed snow and ice over all-seasons.
7) Never rotate tires
from side to side, only front to back.
With any car having the
same size tires at all four wheels, their radial tires can be crossed
from side to side in the rotation pattern. The old front-to-back rule
applied to bias ply tires. Regular tire rotation about every 6,000 to
8,000 miles, promotes more uniform wear for all tires on a vehicle.
Goodyear recently designed a light truck tire system that requires no
rotation, the Wrangler RF-A, which provides a rear tire with a different
tread design from the front tire.
8) Sticking your
fingernail in the tread can help pick the tire with the softest
compounds, and thus, the best adhesion.
It’s sort of like
kicking the tire, but with another part of the anatomy. Tread compounds
only tell part of a tire’s story. Tread pattern, tire shape and the
tire footprint shape on the pavement provide clues to its adhesion
capabilities. Don’t rely on the fingernail test.
9) The government
tests tires for traction, temperature resistance and treader and assigns
grades that are molded onto the sidewall.
Uniform Tire Quality
Grading is a federal law that requires tire manufacturers to grade their
tires for tread wear, traction and temperature resistance. Tire
manufacturers, not the government, test tires and assign their own
grades. Unfortunately, the government has not yet prescribed a formula
for converting the manufacturers test results into grades; therefore the
numbers are not objective. According to the Federal Trade Commission,
treader grades are for comparison purposes only and are not intended to
be converted into anticipated or promised tire mileage.
10) Tires are made of
a single rubber compound.
Several polymers are used
in a tire, depending on their performance characteristics. Run-flat or
extended mobility tires (EMT), for example, use heat-dissipating polymer
reinforcements that stiffen tire sidewalls, while tread compounds affect
traction, treader, rolling resistance and noise. In the case of the
Eagle F1 Steel ultra-high-performance tire, its AATRAX triple polymer
tread compound system provides improved handling and wet and dry
traction without sacrificing treader, snow traction, rolling resistance
tires will overcome deficiencies in the vehicle.
Even premium tires can
show signs of premature or uneven tread wear and imprecise steering when
vehicles have improper wheel alignment or worn suspension parts. Correct
wheel alignment is a must and should be checked periodically. Improper
alignment causes excessive tire wear as well as increasing fuel
consumption. Regular tire rotation also promotes more uniform wear for
all tires on a vehicle.
12) An ultra-low
rolling resistant tire provides outstanding fuel economy.
A tire engineered for low
rolling resistance would provide horrible fuel economy when it is run
under inflated. Running tires 20 percent under inflated increases fuel
usage by as much as 10 percent. That amounts to Americans wasting nearly
4 million gallons of gasoline daily. Tire care is crucial in saving
money at the pump.
13) An undulation on a
tire sidewall is a weak spot that could lead to tire failure.
An undulation is created
where materials overlap each other in the tire carcass, and it actually
is the strongest part of the tire. Still, motorists perceive a
"wave" on the sidewall as a defect. Goodyear’s new
ultra-tensile steel reinforcement eliminates this material splice and
overlap. Ultra-tensile steel should reduce sidewall undulations found in
polyester reinforced tires.
14) Tires are a
low-tech commodity, and price should determine what to buy.
Consider the rain,
run-flat and performance tires on the market today. Time and technology
have improved the quality and value of today’s tires. Price should be
only one consideration, along with the other factors that can enhance
tire value and vehicle handling. For the industry, average passenger
tire life has climbed from 24,000 miles in 1973 to about 47,000 miles
today. No one would want to turn back the clock on tire developments or
prices. On a cost-per-mile basis, tires from the so-called "good
old days" would cost more than three times that of the 65,000-mile
warranted Goodyear Aquatred III radial tire.
15) Before you buy a
car, kick the tires.
It won’t tell you much
about the vehicle or tires, but it will tell you if your shoe padding is
Besides these FAQs, in
light of the recent public controversy about tires, we asked the
Goodyear guys some more specific questions about the various markings of
the sidewalls of the Eagle F1 GS-EMTs on many C5s and those on the tires
of other Corvettes.
We found that although
it's something you probably won't take to bed, a tire sidewall actually
makes for good reading. Consider the wealth of information embedded in
the rubber that covers everything from the auto tire's size to its
"genetics," say Goodyear engineers.
Pretty gripping stuff.
Uh....no pun intended.
Even if it's true that
you can't tell a tire by its sidewall, the numbers and letters on its
sides still can reveal some notable facts about the tire, the Goodyear
folks told us.
We learned that "M+S"
or any combination of the letters M and S signifies mud-and-snow
certification, defined by tread patterns with angled slots and grooves
that are a minimum 25 percent of the footprint. M+S tires are meant to
provide improved starting, stopping and driving performance in the snow,
compared to similar tires not marked M+S.
Manufacturers Association (RMA), which includes Goodyear,
took the global industry lead in 1999 in designating
winter tires that would carry the mountain/snowflake symbol on
the sidewall which looks like this:
This severe snow service
designation is based on traction performance, a more stringent
requirement than the M and S rating.
a tire primarily designed to fit passenger cars. Other letter
possibilities are LT for light truck and T for temporary spare.
Actually, the prefix letter is optional so it might not be included in
P designates a tire
primarily designed to fit passenger cars. Other letter possibilities are
LT for light truck and T for temporary spare. We should point out,
however, the prefix letter is optional, so it might not be included in
The first number in the
size designation, such as the 275 in a P275/40ZR17 tire you might find
on a later C4, is the cross-section width of this tire in millimeters.
The next number in our
example, 40, is the "aspect ratio" or ratio between
cross-section height (from the bead that holds tire on the rim to the
tread) to cross-section width (from sidewall to sidewall at its widest
part). For example, a 275-mm or 10.8-inch-wide tire with a 40 aspect
ratio has a section height of 4.3 inches (10.8x0.4).
R means radial tire
construction. Modern Tire Dealer magazine estimates 99.7 percent
of the passenger tire market is radial. Other possible construction
letterings are B for belted-bias construction and D for diagonal (bias)
construction. Other possible construction letterings are B for
belted-bias construction and D for diagonal (bias) construction.
17 is the wheel diameter
in inches. The range of wheel diameters on today's passenger cars is 12
to 20 inches.
Directional tires, such
as Goodyear's Eagle GS-C and F1 GS-EMT, increase the ability of the
tread design to disperse water from under the tire for improved wet
traction. An arrow on the sidewall, primarily added for the tire
installer, shows the direction that the tire rotates.
Without a chart, the load
index and speed rating can be unreadable. Although the load index
numbers are too numerous to list here, the important thing to remember
is that a higher load index number means a higher load capacity. Never
replace a tire with another tire having a lower load index number.
The speed rating letters
include S for speeds up to 112 mph; T, up to 118 mph; H, up to 130 mph;
V, up to 149 mph; W, up to 168 mph; Y, up to 186 mph and Z, 150 mph and
The speed rating
indicates the maximum speed at which the tire may be operated, but it
does not imply that the vehicle may be safely driven at that speed,
particularly under adverse conditions.
A list of tire components
provides the tire's "genetics," such as the number of tire
plies under the tread and in the sidewalls plus the type of materials
Tire manufacturers are
required to grade their passenger car tires for tread wear, traction and
temperature resistance and assign Uniform Tire Quality Grading Labels
according to regulations established by the National Highway Traffic
Safety Administration (NHTSA). Tire manufacturers, not the government,
test tires and assign their own grades.
The tread wear grade or
number, according to the United States Department of Transportation, is
for comparison purposes only and is not intended as a measure of
anticipated or promised mileage from a specific tire on a specific
vehicle. Since each manufacturer assigns its own number, a tire graded
220 by one maker might not deliver as much actual tread mileage as one
graded 190 by another company. Interestingly, the tread wear grading, is
based upon testing over a 7,200 mile distance on a government-selected,
public highway in Texas.
Temperature grades, A
(the highest), B and C for tires that are properly inflated and loaded,
represent a tire's resistance to heat and its ability to dissipate heat
when tested under controlled laboratory conditions. Sustained high
temperature reduces tire life. Excessive temperature may lead to sudden
Traction grades, AA(the
highest), A, B and C, represent a tire's ability to stop on wet asphalt
and concrete. A C-graded tire may have comparatively poor wet-traction
performance. Goodyear’s Aquatred 3 tire recently became the company’s
first broad market tire to earn the AA grade.
The DOT symbol certifies
compliance with the U.S. Department of Transportation tire safety
standards and is followed by a tire identification or serial number. For
tires manufactured before the year 2000, the last three numbers identify
the week and year of manufacture, its so-called birthday. For example,
459 means the 45th week of 1999.
Beginning in 2000, the
last four numbers identify the week and year of manufacture. For
example, 3500 means the 35th week of 2000.
Other characters in the serial number are the tire maker's coding
for tire size and type and manufacturing plant.
Maximum load limits and
associated maximum cold inflation pressures are indicated in both metric
and English units. Exceeding a tire's load limit affects handling, tire
life and fuel economy.
operation, follow the vehicle manufacturer’s inflation
pressure recommendations (listed in some owner’s manuals and
always listed on the vehicle placard located either on the
driver’s side door post or in the glove box) and not the
maximum inflation molded on the sidewall. Tire inflation should
be increased when adding to vehicle load, such as luggage or a
camper in tow, before setting out on a long trip or for any
sustained high speed driving, but never exceed the maximum
inflation pressure stamped on the tire sidewall.
sidewall might not tell consumers the whole story in making a
purchase decision, the writing on the sidewall and reputable
tire retailers can help them make informed choices, the Goodyear
people told us.