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| What do I need to know about aspect ratio? | ||
Answer: UTQGL stands for Uniform Tire Quality Grade Labeling, a system that classifies tires as to treadwear, traction and heat
resistance. Each tire manufacturer performs its own tests in these categories, in accordance with government prescribed test
procedures. Based on these tests, each manufacturer then assigns grades, which are branded on the tire sidewall, Example:
Treadwear 400 Traction AA Temperature A
Question: How is the treadwear grade determined?
Answer: Treadwear tests are performed on a government-prescribed 400-mile section of public highways near San Angelo, Texas.
Test vehicles travel the same course at the same time, so all tires experience the same conditions. During the test, tread groove
depths are measured every 800 miles. The same procedure is followed with a set of reference control tires. After 7200 miles of
testing, the tread depths of test tires and reference control tires are compared and the test tires are graded on the basis of relative
wear.
Question: If my treadwear grade is 400, how long will the tire last?
Answer: The best way to understand a treadwear grade is to compare the grade of one tire with another. For instance, a tire with a
treadwear grade of 400 might be expected to last twice as long as a tire with a treadwear grade of 200. However, there is no way of
accurately predicting how long your tires will last. This is determined not only by tire quality, but also by road surface quality, personal
driving habits, tire inflation pressures, wheel alignment and frequency of tire rotation. The treadwear grade is only a reference point to
indicate how one tire performs in relative terms to another on the government-controlled treadwear course. It was never intended to
project the exact mileage a particular tire might deliver.
Question: The traction grade on my tire is A. what does that tell me?
Answer: Put simply, it grades the tire's ability to stop a car in a straight line on a wet test surface. For example, a tire with an AA grade
will stop more quickly in a straight line on wet pavement than a tire with a C grade. Note that these traction tests are performed on
government-maintained concrete and asphalt skid pads that have a specified degree of wetting to simulate most road surfaces. These
test do not measure braking under dry pavement conditions, or cornering traction under any conditions. Traction grades range from AA,
A, B to C with AA being the best.
Question: Is the temperature grade on my tire important?
Answer: Yes, it represents a properly maintained tire's ability to dissipate heat under controlled indoor test wheel conditions. A tire is
graded "C" if it meets the minimum performance required by the Department of Transportation (DOT). Grades of "B" and "A" represent
higher levels of performance than the minimum required by the DOT. All tires must meet the minimum speed requirement of 85 mph set
by Federal Motor Vehicle Safety Standard 109.
Question: Is tire rotation helpful?
Answer: Yes, because tire rotation can provide more even tire wear, maximize tire life, and provide better handling for the life of your
tires, if the correct tire rotation guidelines are followed. For example: if you drive a front-wheel-drive car, your front tires absorb most of
the forces associated with load, acceleration, driving, steering and braking, all of which contribute to tire wear. The difference in wear
rate between the front and rear tires on a front-wheel-drive car can be as much as three to one. to obtain relatively equal mileage on
front and rear tires, you should rotate your tires every 6,000 to 8,000 miles. If you notice any signs of premature, irregular or uneven
wear patterns, rotate the tires more often. Ask your tire dealer to recommend a tire rotation pattern that is right for your vehicle.
Question: May I use my "temporary spare only" tire in my tire rotation pattern?
Answer: No, temporary means just that. For proper and safe rotation, only use tires of a like construction and size. temporary spares are
of a different size and construction than the other tires on your vehicle and require much higher inflation pressures, However, if you have
a regular, full-size spare in your trunk, you may include that in you rotation pattern, Check with you tire dealer for proper procedures.
Question: Is tire sizing nomenclature complicated, or is it just me?
Answer: It is assuredly not just you! Four sizing systems are in use for passenger tires: P-Metric, European Metric, Millimetric and Alpha
Numeric. The most widely used in the U.S. is the P-Metric system. If the size branded on your sidewall is arranged as follows P215/65R15
95S (the specific numbers may vary), then you have a p-Metric size tire. The P stands for passenger car tire; the 215 is the tire's "section
width" - its width at the widest point - in millimeters; the 65 is the tire's "aspect ratio" - the percentage of its sidewall height relative to its
section width - and the R is for radial construction. The 15 is the rim diameter, in inches, and the 95S is the service description (95 being
the load index - which corresponds to a table of maximum load capacity in pounds - and S being the speed rating). And this just describes
one sizing system; we have three more to go!
Question: Then, what's the European or Millimetric size?
Answer: Essentially, this system is a conversion of the original (and now obsolete) numeric sizing system from inches to millimeters. If the
tire size on your sidewall is arranged like 185/70R14 88S, (again, your specific numbers may vary), then you have a European Metric size,
The 185 is the tire's section width, in millimeters, while the 70 indicates aspect ratio. Next, the 14 is the rim diameter, in inches, and the
88S is the service description (load index and speed rating). R simply indicates that it is a radial construction.
Your tire is a millimetric size if the size is arranged like 240/55R390. In this example the 240 is the section width in millimeters, the 55 is
the aspect ratio, the R means the tire is of radial construction and the 390 is the rim diameter, in millimeters.
Question: What should I know about light truck tire sizing?
Answer: There are three light truck sizing systems in use today. The LT-Metric light truck sizing system mirrors the P-Metric system for
passenger tires. For instance, a size such as LT35/75R15/C on your sidewall breaks out this way: the LT stands for light truck; the 235,
your tire's section width in millimeters; the 75, aspect ratio; the R, radial construction and 15, the rim diameter in inches. Last, the C
represented the tire's load range.
Keep in mind that nearly 50% of all new vehicles built in the U.S. are not "cars" in the traditional meaning, but includes minivans, pickups
and SUVs. Nonetheless, many are being fitted with P-Metric passenger car tires, which tend to emphasize ride comfort and fuel economy.
However, many light truck vehicles require higher load carrying capacity than offered by P-Metric tires primarily for commercial purposes,
and thus come fitted with light-truck-sized tires.
Question: The tire size on my pickup reads 31x10.50R15LT/C. What does this mean?
Answer: It means you have a light truck "flotation" tire, designed to deliver better traction on sand and soft soil found in watery off-road
situations. The 31 indicates the tire's overall diameter in inches while the 10.50 shows the the tire's section width in inches. The R means
the tire is a radial, the LT stands for light truck tire and the C indicates the tire's load range.
Question: When is the light truck numeric sizing used?
Answer: This older sizing system is still used on older commercial vehicles. The tire size branded on the sidewall looks like this: 9.50R16.5SLT/D.
In this example, the 9.50 represents the tire's section width in inches; the R, radial construction; the 16.5, the rim diameter in inches; the
LT, Light Truck and the D, the tire's load range.
Question: What do I need to know about aspect ratio?
Answer: Simply put, the lower the aspect ratio, the shorter the sidewall, and in most cases, the quicker the steering response, In
engineering terms, a tire's aspect ratio is the dimensional relationship of the tire's section height to section width, expressed as a
percentage. For example: a tire with an aspect ratio of 75 has a sidewall which is 75% as tall as the tire is wide, at its widest point.
A 50 aspect ratio (also called a 50-series tire) is half as tall as it is wide.
Question: How do I know when I need new tires?
Answer: Ask your Michelin Americas Small Tire dealer to replace your tires if the tread depth is 2/32nds of an inch or less as indicated
by the tire "wear bars" molded into the tread grooves. Also known as treadwear indicators, tire wear bars are raised areas in the tread
grooves, which become even with the tread surface when the tire is worn to 2/32nds. You can't miss them. Most states require replacement
of tires worn to this tread depth because of the increased possibility of tire failure, sudden traction loss in the rain and virtually no
traction in snow.
In southern states where torrential downpours test a tire's ability to get rid of water through its tread grooves, you would do well to replace
tires before they reach 2/32nds. in snow belt areas, replacement before you to the wear bars is also wise. In deep snow, the tire must
be able to compress and clean out packed snow from its tread grooves.
Question: How should I choose tires right for me?
Answer: Start by checking the vehicle tire placard or your Vehicle Owner's Manual. Both list the original equipment and optional tire
types and sizes suitable for your vehicle. However, let's say your SUV originally came with P-Metric all-season tires and you live in a
heavy-snow-belt area. Think about replacing your all-season tires with a more aggressive LT-Metric Mud&Snow type tire. Or, if you
live in the farm belt where mud is an issue, think about a mud-terrain type tire. Because there are so many tire types to consider, it
may be wise to discuss your tire needs with your dealer.
Question: Who should install my new tires?
Answer: Make certain the installer you select is associated with a major tire manufacturer such as Michelin North America, Inc., or tire
brands such as BFGoodrich® or Uniroyal®. Look on the walls of the tire outlet for certificates of accomplishment earned by the outlet's
personnel and issued by one of these brands. Of course, check the cleanliness of the outlet from its showroom to its service bays.
Also, ask about a guarantee against any wheel damage during tire mounting. If such a guarantee is not offered, strongly consider
taking your business elsewhere.
Question: How do I know what inflation pressure to use?
Answer: First, check the vehicle placard in your vehicle. The automobile manufacturer has already determined the best inflation pressure
for use in your tires under standard operating conditions. The air pressure should never be below the minimum listed on the vehicle
placard or above the maximum recommended inflation pressure branded on the tire sidewall. Our advice is to use the pressure listed
on the placard.
Question: How often should I check inflation pressure in my tires?
Answer: You should check the inflation pressure in your tires, including the spare, at least once a month and always before extended
driving. Check the pressure when your tires are cold - that is, when your vehicle has been parked for at least three hours. If necessary,
add air to inflate your tires to the pressure(s) specified on the vehicle placard. Since this reading will be most accurate with cold tires,
drive to the nearest source of air whenever possible.
Never 'bleed" or reduce inflation pressure when your tires are hot. When tires heat up from driving, it is normal for inflation pressures
to increase above recommended cold inflation pressure levels. But if you let air out of a hot tire, it will be under-inflated when it cools down.
Also use a high-quality air pressure gauge to check your tires, don't trust your eyes. You can't tell by looking if a tire is properly inflated.
A rule of thumb, for highway use, all passenger and light truck tires should be inflated at or more than 20 psi. For any 16.5-inch rim
diameter light truck tire, the minimum highway inflation pressure is 30 psi.
Question: What might happen if I run my tires under-inflated or over-inflated?
Answer: Under-inflation can cause extreme sidewall flexing. the result may be dangerous heat buildup that can lead to premature tire
failure. Over-inflation can cause your tires to be more susceptible to impact damage. and either under-inflation or over-inflation may
adversely affect vehicle handling and treadwear.
Question: What are tire speed ratings all about?
Answer: Officially, the speed rating of a tire indicates the highest speed at which the tire can carry a specified load under specified
conditions. Letters from A to Z symbolize a tire's certified speed rating, ranging from 3 mph to above 186 mph. The speed ratings
most commonly in use are:
Q 100 mph V 149 mph
R 106 mph W 168 mph
S 112 mph Y 186 mph
T 118 mph Z Zr speed capability above 149 mph.
ZR_When ZR appears in the tire size designation along with a service description - such as P275/40ZR17 93W - the maximum speed
rating (indicated by the "W" in "93W") indicates the tire's speed rating - in this case, 168 mph.
In this latest effort to standardize tire designations, all ratings except unlimited Z-speed rated tires incorporate the speed symbol and
load index in the tire;s service description. Example: P225/60R15 95H. the 95H is the tire's service description indicating a maximum
load carrying capacity of 1521 lbs. and a maximum speed rating of 130 mph. While all tires are speed rated to indicate speed capabilities
in excess of national speed limits, Michelin North America, Inc., does not endorse the operation of any vehicle in an unsafe or
unlawful manner.
Question: Why are speed-rated tires so expensive?
Answer: Because speed-rated tires must meet ultra-high performance demands, they generally have been engineered to provide
dramatically better handling. A V-speed-rated tire, for instance, has been built with state-of-the-art tread designs, tire profiles, carcass
materials, and construction, using exotic tread polymers and compounds. While Q, S, or non-speed-rated tires meet or exceed all DOT
requirements, they generally do not feature the advanced and costly construction built into ultra-high performance speed-rated tires.
Question: What if I replace and H-rated tire with an S-rated tire?
Answer: You should replace original equipment speed-rated tires with tires of the same or higher speed rating if the speed rating of the
vehicle is to be maintained. If you replace H-rated tires (capable of speeds up to 130 mph) with S-rated tires (capable of speeds up to
112 mph), you need to know and inform the vehicle owner that the handling of their vehicle will be different, and that now, its maximum
speed capability is limited to that of the lowest speed-rated tire on the vehicle. In this example, you would have lowered the speed
capability of your vehicle from 130 mph to 112 mph.
Question: I am buying two new tires. Where do they go, front or rear?
Answer: Always on the rear. In a cornering maneuver on wet pavement, if your front tires lose grip first, your vehicle will tend to lose
control by going straight, even in a turn. This is understeer, which can be controlled by slowing down and steering in the direction of
the turn. This will allow your car to come back into line.
But if the rear tires lose grip first, your vehicle could spin, which is oversteer and more difficult to control. this requires you to make
quick, precise steering corrections in the opposite direction of the turn, not a natural reaction. It is easier to control understeer
than oversteer.
For the record, the best choice to make when replacing tires is to buy four new tires, all the same brand, type and size.
Question: If I buy just one tire, what should I buy, and where should it go?
Answer: The only sound reason to buy just one tire is to replace one tire, damaged by an accident or road hazard, in an otherwise
good set of four. You should always buy the same size, type, brand, and tread design as the tire you're replacing. An all-season
tire should be replaced with an all-season tire. A Mud&Snow tire should be replaced with a Mud&Snow tire, an H-speed-rated tire
should be replaced with an H-speed-rated tire. In this way you will enjoy a safer, more satisfying driving experience.
Question: What's the difference between an all-season tire and an all-terrain type tire?
Answer: An all-season tire is designed with a long lasting, aggressive tread pattern designed to get rid of water and snow,
balancing the wet and snow traction capability with dry pavement performance. It generally features lots of biting edges that
enhance snow and wet traction, It can even be branded as an M&S tire (Mud and snow.)
An all-terrain type tire is a light truck tire that has been designed with an even more aggressive tread pattern. This type of tire
may be driven on- or off-road in virtually any type of weather and road condition. In rain and on mud, an all-terrain tire's open,
self-cleaning tread provides excellent traction, and its rugged edges grip on rocky and uneven terrain.
Question: Should I be concerned about tire load carrying capacity?
Answer: If you replace original equipment tires with the same size and type replacement tires, your newest tires will be able to
handle the weight of your vehicle and its maximum allowable load. However, if you switch from an LT-Metric to a P-Metric or if you
are changing sizes, you should consult your tire dealer. He or she will review your tire selection against industry tire load and
inflation tables to make certain you aren't installing tires incapable of supporting your vehicle and its load. A replacement tire
must always meet or exceed the load carrying capacity of the original equipment tire.
Question: Can changing tire sizes confuse my vehicle's on-board computers?
Answer: It can if you substantially change the overall diameter of your tires. Maintaining the original, specified diameters as
closely as possible ensures that your on-board computers will function properly and thereby effectively manage such systems
as your anti-lock braking system, traction control, fuel management system, electronically controlled automatic transmission and
electronic handling stability system. Changing tire diameters sends erroneous readings to the computers. These systems won't
fail, but they will be impacted to varying degrees. If you have any questions about this potentially troublesome issue, contact
your tire dealer.