| Tire Information Tire Tech
A little basic knowledge about tires can help you make a more informed descision about the
next tire purchase.
THE IMPORTANCE OF AIR PRESSURE
Proper inflation pressure in your tires is very important for both safety reasons and to
get the maximum life from them.
An under inflated tire allows the sidewalls of the tire to flex excessively as it rolls
down the road. This flexing causes the tire to heat up beyond the range of temperatures it
was designed to operate within.
At best the excessive heat will cause the tire to wear out up to 25% quicker and at worst
will cause the sidewall of the tire to fail.
Over inflated tires are more susceptible to impact damage as the tire cannot properly flex
to absorb impacts with road hazards. You vehicle owners manual will provide you with
proper inflation information.
PLUS SIZING
SPEED RATING
TIRE ROTATION
TIRE SIZES
UTQG RATING SYSTEM
CALCULATING TIRE DIMENSIONS
PLUS SIZING
Plus sizing is a quick and easy way to improve not only the handling
characteristics of your vehicle but also the appearance.
Example: Your vehicle comes stock with a 195/60R15. This tire has a 24.2 inch diameter and
has a sidewall that is 4.6 inches tall. The correct plus 1 size would be 205/50R16. This
tire has a 24.1 inch diameter and has a 4.0 inch sidewall. The correct plus 2 size would
be 205/45R17. This tire would have a 24.3 inch diameter with a 3.6 inch sidewall. As you
can see the outside of the tire has remained within 1/10 of an inch but the wheel has
increased in diameter by 2 inches. The new tire also has a tread footprint that is
approximately .75" wider. This has a couple of benefits. One is that with the
increased footprint your vehicle will have better grip in cornering. Two is that the
shorter side wall of the plus sized tire will be more rigid allowing your vehicle to
respond more quickly to your steering input. The new lower profile tire will also give
your vehicle a sporty more aggressive appearance. Your local Tire Factory location will
have all the specific plus sizing information for your vehicle.
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SPEED RATING
Speed rating is a government regulated measurement which is given to a tire for meeting
minimum standards for reaching and sustaining certain speeds. Generally a higher speed
rated tire will have better handling. Tire Factory does not recommend downgrading the
speed rating on your vehicle. Doing so may result in undesired handling qualities. Your
vehicle was designed to use a minimum speed rated tire to handle properly. Installing a
higher speed rated tire will help the handling of your vehicle especially in corning. Make
sure however, that you do not mix different speed rated tires on the same vehicle, as this
will cause handling problems. Below is a list of the speed rating letters and the speeds
which corresponds to the letters. These speeds are the speeds at which the tire was tested
and not recommended for real world driving.
Q up to 100mph
S up to 112mph
T up to 118mph
U up to 124mph
H up to 130mph
V up to 149mph
W up to 168mph
Y up to 186mph
Z 149mph plus
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THE IMPORTANCE OF TIRE ROTATION
Regular tire rotations are extremely important in maintaining the useful life of the tires
on your vehicle by providing more uniform wear. Regular interval tire rotations will help
you get the most life out of a set of tires. The interval of rotation can vary from every
3,000 miles to every 8,000 miles depending on the vehicle and the type of driving that you
do. Your local Tire Factory location will help you to determine the interval that will
give you optimal results. Some vehicles are equipped with different sized tires on the
front and rear or with special unidirectional tires and will require special rotation
patterns for the tires. Once again your local Tire Factory will be able to provide you
with the proper rotation regardless of the vehicle.
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SECTION WIDTH
With a P215/65R15 95H as an example size the "215" would be the section width of
the tire. The section width is a measurement in millimeters across the widest point of the
tire when it is mounted on a specified width of wheel. The example tire would be 215mm or
approximately 8.5 inches wide at its widest point.
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THE UTQG RATING SYSTEM
The Federal Government established the UTQG (Uniform Tire Quality Grading) system to
attempt to better inform consumers about the tires they are purchasing. It can be a useful
tool in comparing tires from the same manufacturer. The UTQG is not a warranty or
guarantee that a tire will last for a certain number of miles. It is simply a way to
compare tires in three ways: Treadwear, traction, and temperature. The reason the UTQG is
not good for comparing tires from different manufacturers is that the numbers and letters
that make up the grading system are all relative to other tires by that manufacturer.
Example: The first number represents the tread wear of the tire. If a certain manufacturer
ranks their lowest mileage tire at 150 they would rank a tire that lasts twice as long at
300. If another manufacturer ranked their lowest tire at 250 they would rank a tire that
lasted twice as long at 500. This does not mean that the 500 tire is going to last any
longer than the 300 tire. The next letter(s) in the UTQG are for measuring the tires
ability to stop in a straight line on wet pavement. This is not a measurement of the
cornering ability of a tire. The rankings for traction from best to worst are AA,A,B,C.
The last letter in the UTQG is used to measure the tires ability to dissipate heat. A tire
that quickly dissipates heat will generally last longer than a tire that dissipates heat
more slowly. The rankings for temperature from best to worst are A,B,C.
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CALCULATING TIRE DIMENSIONS
Calculating the dimensions of a tire is actually not that complicated.
Example: P215/65R15
The section width of the tire is 215 millimeters which can be converted to inches by
dividing by 25.4. The height of each sidewall of the tire is 65% or the 215mm width so
calculations would look like:
215*.65 = 139.75mm (sidewall height)
139.75*2=279.5mm(Height of top and bottom sidewall of the tire)
279.5/25.4 = 11 (Convert sidewall height to inches)
11+15(rim height of tire) = 26 inches (overall diameter of tire)
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