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Load Index:An assigned number ranging from1 to 279 that corresponds to the load carryingcapacity of a tire.
Maximum Inflation Pressure:The maximum airpressure to which a cold tire can be inflated. Themaximum air pressure is molded onto the sidewall.
Maximum Load Rating:The load rating for a tireat the maximum permissible inflation pressurefor that tire.
Maximum Loaded Vehicle Weight:The sum ofcurb weight, accessory weight, vehicle capacityweight, and production options weight.
Normal Occupant Weight:The number ofoccupants a vehicle is designed to seat multipliedby 150 lbs (68 kg). SeeLoading the Vehicle onpage 5-18.
Occupant Distribution:Designated seatingpositions.
Outward Facing Sidewall:The side of anasymmetrical tire that has a particular side thatfaces outward when mounted on a vehicle. Theside of the tire that contains a whitewall, bearswhite lettering, or bears manufacturer, brand,and/or model name molding that is higher or deeperthan the same moldings on the other sidewall ofthe tire.
Passenger (P-Metric) Tire:A tire used onpassenger cars and some light duty trucks andmultipurpose vehicles.
Recommended Inflation Pressure:Vehiclemanufacturer’s recommended tire inflationpressure as shown on the tire placard. SeeInflation - Tire Pressure on page 6-54andLoadingthe Vehicle on page 5-18.
Radial Ply Tire:A pneumatic tire in which theply cords that extend to the beads are laid at90 degrees to the centerline of the tread.
Rim:A metal support for a tire and upon whichthe tire beads are seated.
Sidewall:The portion of a tire between the treadand the bead.
Speed Rating:An alphanumeric code assigned toa tire indicating the maximum speed at which atire can operate.
Traction:The friction between the tire and theroad surface. The amount of grip provided.
Tread:The portion of a tire that comes intocontact with the road.
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Treadwear Indicators:Narrow bands, sometimescalled wear bars, that show across the tread ofa tire when only 1/16 inch (1.6 mm) of treadremains. SeeWhen It Is Time for New Tires onpage 6-64.
UTQGS (Uniform Tire Quality GradingStandards):A tire information system thatprovides consumers with ratings for a tire’straction, temperature, and treadwear. Ratings aredetermined by tire manufacturers usinggovernment testing procedures. The ratings aremolded into the sidewall of the tire. SeeUniformTire Quality Grading on page 6-67.
Vehicle Capacity Weight:The number ofdesignated seating positions multiplied by 150 lbs(68 kg) plus the rated cargo load. SeeLoadingthe Vehicle on page 5-18.
Vehicle Maximum Load on the Tire:Load on anindividual tire due to curb weight, accessoryweight, occupant weight, and cargo weight.
Vehicle Placard:A label permanently attached toa vehicle showing the vehicle’s capacity weightand the original equipment tire size andrecommended inflation pressure. See “Tire andLoading Information Label” underLoadingthe Vehicle on page 5-18.
Inflation - Tire Pressure
Tires need the correct amount of air pressure tooperate effectively.
Notice:Do not let anyone tell you thatunder-inflation or over-inflation is all right. It isnot. If your tires do not have enough air(under-inflation), you can get the following:
•Too much flexing
•Too much heat
•Tire overloading
•Premature or irregular wear
•Poor handling
•Reduced fuel economy
If your tires have too much air (over-inflation),you can get the following:
•Unusual wear
•Poor handling
•Rough ride
•Needless damage from road hazards
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A Tire and Loading Information label is attached tothe vehicle’s center pillar. This label lists yourvehicle’s original equipment tires and shows thecorrect inflation pressures for your tires when theyare cold. The recommended cold tire inflationpressure, shown on the label, is the minimumamount of air pressure needed to supportyour vehicle’s maximum load carrying capacity.
For additional information regarding how muchweight your vehicle can carry, and an example ofthe Tire and Loading Information label, seeLoading the Vehicle on page 5-18. How you loadyour vehicle affects the vehicle handling andride comfort, never load your vehicle with moreweight than it was designed to carry.
When to Check
Check your tires once a month or more. Do notforget to check the spare tire. If your vehicle has acompact spare tire, it should be at 60 psi (420 kPa).For additional information seeSpare Tire onpage 6-90.
How to Check
Use a good quality pocket-type gage to check tirepressure. You cannot tell if your tires areproperly inflated simply by looking at them. Radialtires may look properly inflated even when theyare under-inflated. Check the tire’s inflationpressure when the tires are cold. Cold means yourvehicle has been sitting for at least three hoursor driven no more than 1 mile (1.6 km).
Remove the valve cap from the tire valve stem.Press the tire gage firmly onto the valve toget a pressure measurement. If the cold tireinflation pressure matches the recommendedpressure on the Tire and Loading Informationlabel, no further adjustment is necessary. If theinflation pressure is low, add air until you reach therecommended amount.
If you overfill the tire, release air by pushing onthe metal stem in the center of the tire valve.Re-check the tire pressure with the tire gage.
Be sure to put the valve caps back on the valvestems. They help prevent leaks by keeping out dirtand moisture.
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Temperature – A, B, C
The temperature grades are A (the highest), B,and C, representing the tire’s resistance tothe generation of heat and its ability to dissipateheat when tested under controlled conditions on aspecified indoor laboratory test wheel. Sustainedhigh temperature can cause the material of the tireto degenerate and reduce tire life, and excessivetemperature can lead to sudden tire failure.The grade C corresponds to a level of performancewhich all passenger car tires must meet underthe Federal Motor Vehicle Safety StandardNo. 109. Grades B and A represent higher levelsof performance on the laboratory test wheelthan the minimum required by law. It should benoted that the temperature grade for this tireis established for a tire that is properly inflated andnot overloaded. Excessive speed, underinflation,or excessive loading, either separately or incombination, can cause heat buildup and possibletire failure.
Wheel Alignment and Tire Balance
The tires and wheels on your vehicle were alignedand balanced carefully at the factory to give you thelongest tire life and best overall performance.Adjustments to wheel alignment and tire balancing willnot be necessary on a regular basis. However, ifyou notice unusual tire wear or your vehicle pulling toone side or the other, the alignment might need tobe checked. If you notice your vehicle vibrating whendriving on a smooth road, the tires and wheelsmight need to be rebalanced. See your dealer/retailerfor proper diagnosis.
Wheel Replacement
Replace any wheel that is bent, cracked or badly rustedor corroded. If wheel nuts keep coming loose, the wheel,wheel bolts and wheel nuts should be replaced. If thewheel leaks air, replace it. Some aluminum wheels cansometimes be repaired. See your GM dealer/retailer ifany of these conditions exist.
Your GM dealer/retailer will know the kind of wheelyou need.
Each new wheel should have the same load-carryingcapacity, diameter, width, offset and be mountedthe same way as the one it replaces.
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