< Previous | Contents | Next >
Mixing tires of different sizes (other than those originally installed on
the vehicle), brands, or types may
cause loss of control of the vehicle, resulting in a crash or other vehicle
damage. Use the correct size, brand, and type of tire on all four wheels.
{ Warning
Using bias-ply tires on the
vehicle may cause the wheel rim flanges to develop cracks after
many miles of driving. A tire
and/or wheel could fail suddenly and cause a crash. Use only
radial-ply tires with the wheels on the vehicle.
If the vehicle tires must be
replaced with a tire that does not have a TPC Spec number, make
sure they are the same size, load
range, speed rating, and
construction (radial) as the original tires.
Vehicles that have a tire pressure monitoring system could give an
inaccurate low-pressure warning if non-TPC Spec rated tires are
installed. See Tire Pressure Monitor Operation 0 359.
The Tire and Loading Information label indicates the original
equipment tires on the vehicle. See Vehicle Load Limits 0 211.
Different Size Tires and Wheels
If wheels or tires are installed that are a different size than the original
equipment wheels and tires, vehicle performance, including its braking, ride and handling characteristics,
stability, and resistance to rollover may be affected. If the vehicle has
electronic systems such as antilock brakes, rollover airbags, traction
VEHICLE CARE 365
control, electronic stability control, or All-Wheel Drive, the performance
of these systems can also be affected.
{ Warning
If different sized wheels are used, there may not be an acceptable
level of performance and safety if tires not recommended for those
wheels are selected. This increases the chance of a crash and serious
injury. Only use GM specific wheel and tire systems developed for the vehicle, and have them properly
installed by a GM certified technician.
See Buying New Tires 0 364 and
Accessories and Modifications 0 307.
Uniform Tire Quality Grading
The following information relates to the system developed by the
United States National Highway Traffic Safety Administration
(NHTSA), which grades tires by
366 VEHICLE CARE
treadwear, traction, and
temperature performance. This
applies only to vehicles sold in the United States. The grades are
molded on the sidewalls of most passenger car tires. The Uniform Tire Quality Grading (UTQG)
system does not apply to deep
tread, winter tires, compact spare tires, tires with nominal rim
diameters of 10 to 12 inches (25 to 30 cm), or to some
limited-production tires.
While the tires available on
General Motors passenger cars and light trucks may vary with
respect to these grades, they must also conform to federal safety
requirements and additional
General Motors Tire Performance Criteria (TPC) standards.
Quality grades can be found where applicable on the tire sidewall
between tread shoulder and maximum section width. For example:
Treadwear 200 Traction AA Temperature A
All Passenger Car Tires Must Conform to Federal Safety
Requirements In Addition To These Grades.
Treadwear
The treadwear grade is a
comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded
150 would wear one and one-half (1½) times as well on the
government course as a tire graded 100. The relative
performance of tires depends upon the actual conditions of their use, however, and may
depart significantly from the norm due to variations in driving habits, service practices and differences
in road characteristics and climate.
Traction
The traction grades, from highest to lowest, are AA, A, B, and C.
Those grades represent the tire's
ability to stop on wet pavement as measured under controlled
conditions on specified
government test surfaces of asphalt and concrete. A tire
marked C may have poor traction performance. Warning: The
traction grade assigned to this tire is based on straight-ahead braking traction tests, and does not
include acceleration, cornering, hydroplaning, or peak traction characteristics.
Temperature
The temperature grades are A (the highest), B, and C, representing
the tire's resistance to the
generation of heat and its ability to dissipate heat when tested
under controlled conditions on a specified indoor laboratory test
wheel. Sustained high temperature