A Tire Performance Criteria (TPC) specification number is molded in the sidewall near the tire size of all original equipment tires. The specification number assures that the tire meets the following GM performance standards:
| • | Traction |
| • | Endurance |
| • | Dimension |
| • | Noise |
| • | Handling |
| • | Rolling Resistance, etc. |
Usually, each tire size has a specific TPC number assigned. Replacement tires should match the original tires for the following:
| • | Same size |
| • | Same speed rating |
| • | Same load range |
| • | Same construction |
Replace the original tires with tires of the same TPC specification number. Use of any other tire size or tire type may seriously affect any or all of the following:
| • | Affect the ride |
| • | Affect the handling |
| • | Affect the speedometer/odometer calibration |
| • | Affect the vehicle ground clearance |
| • | Affect the tire clearance to the body and chassis |
Passenger Tire Service Description
Most tires have a service description branded on the sidewall after the tire size. The service description consists of two parts:
| • | The load index is a number usually between 75 and 115. The load index number defines the tire's load capacity at maximum inflation. The higher the number the greater the load capacity. |
| • | The speed symbol is the letter between P and Z. The speed symbol letter defines the speed capacity of the tire. The speed symbol letter is part of the tire size with some V and Z rated tires. The higher the letter the greater speed capability. |
Tire companies have charts which define equivalent loads and speed for all load indexes and speed symbols that make up the tire service description.
Important: Never install replacement tires that are a smaller size or a lesser speed rating than the original equipment. The speed ratings apply when the tire is fully inflated. An under-inflated tire will not meet its speed rating capability. The chart below shows the common speed rating on tires used by General Motors.
Speed Symbol | Maximum Speed (km/h) | Maximum Speed (mph) |
|---|---|---|
S | 160 | 112 |
T | 190 | 118 |
U | 200 | 124 |
H | 210 | 130 |
V | 240 | 149 |
Z | Over 240 | Over 149 |
Inspection Procedure
Replace tires if any of the following occurs:
- Replace the tire if worn to a point where the cord or fabric shows.
- Replace the tire if 1.6 mm (1/16 in) or less tread remains. Tires have built-in tread wear indicators that appear between the tread grooves when the tread is 1.6 mm (1/16 in). Replace the tire if the indicators appear in two or more adjacent grooves at three spots around the tire.
- Replace the tire if the tread or sidewall is cracked.
- Replace the tire if the tread or sidewall is cut.
- Replace the tire if the tread or sidewall is snagged deep enough to expose the cord or fabric.
- Replace the tire if the tire has a bump.
- Replace the tire if the tire has a bulge.
- Replace the tire if the tire has a split.
- Do not replace a tire with slight sidewall indentations. Slight sidewall indentations are normal and should not affect the ride.
- Replace the tire if the tire has a puncture.
- Replace the tire if the tire has a cut.
- Replace the tire if the tire has damage that cannot be correctly repaired because of the size or because of the location of the damage.
