GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Tires and Wheels

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TIRE ROTATION



See Figure 1

Tire wear can be equalized by switching the position of the tires about every 6,000 miles. Including a conventional spare in the rotation pattern can give up to 20% more tire life.


CAUTION
Do not include the new Space Saver® or temporary spare tires in the rotation pattern. These tires are designed ONLY to get you to the next service facility after a flat tire; they are NOT designed for high speed or extended driving.

There are certain exceptions to tire rotation, however. Studded snow tires should not be rotated, and radials should be kept on the same side of the vehicle, maintaining the same direction of rotation. The belts on radial tires get set in a pattern after they accumulate mileage, and if the direction of rotation is reversed, it can cause a rough ride, vibration and possible ill handling.



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Fig. Fig. 1: Tire rotation patterns.

TIRE DESIGN



When buying new tires, give some thought to the following points about tire design, especially if you are considering a switch to larger tires or a different profile series:

  1. All four tires must be of the same construction type. This rule cannot be violated. Radial, bias, and bias belted tires must not be mixed.
  2.  
  3. The wheels should be the correct width for the tire. Tire dealers have charts of tire and rim compatibility. A mismatch will cause sloppy handling and rapid tire wear. The tread width should match the rim width (inside bead to inside bead) within an inch. For radial tires, the rim width should be 80% or less of the tire (not tread) width.
  4.  
  5. The height (mounted diameter) of the new tires can change speedometer accuracy, engine speed at a given road speed, fuel mileage, acceleration, and ground clearance. Tire manufacturers furnish full measurement specifications.
  6.  
  7. The spare tire should be usable, at least for short distance and low speed operation, with the new tires.
  8.  
  9. There should not be any body interference when loaded, on bumps or in turns.
  10.  

TIRE STORAGE



Store tires at a proper inflation pressures if they are mounted on wheels. Mark radial and studded snow tires with an arrow showing direction of rotation so they can be mounted the same way. All tires should be kept in a cool, dry place. If tires are stored in the garage or basement, do not let them stand on a concrete floor; lay them down on strips of wood.

TIRE INFLATION



See Figures 2, 3, 4 and 5

Tire inflation is probably the most ignored area of auto maintenance. Gasoline mileage can drop as much as 0.8% for every 1 pound per square inch (psi) of under inflation. Proper tire inflation is also a very important factor in the handling and safety of the vehicle. Tire life is also affected by air pressure.



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Fig. Fig. 2: Radials have a slight "bulge" when properly inflated.

Tires should be checked weekly for proper air pressure. A chart, located either in the glove compartment or on the driver's or passenger's door, gives the recommended inflation pressures for your vehicle depending on type of tires used (radial or bias-ply) and whether the vehicle is loaded or unloaded.

Tire pressures should be checked before driving when the tires are still cool. Every 10°F rise (or drop) in tire temperature means a difference of 1 psi, which explains why your vehicle's tires look low on a cold morning. Two items should be a permanent fixture in every vehicle's glove compartment; a tire pressure gauge and a tread depth gauge. Never trust the gauge that is built into service station air pumps; they are notoriously inaccurate.



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Fig. Fig. 3: Tread wear indicators are built into the tire tread and appear as bands when the tire is worn.



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Fig. Fig. 4: Check the tread depth with a tire gauge.



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Fig. Fig. 5: A penny can also be used to approximate tread depth. If the top of Lincoln's head is visible in two adjacent grooves, replace the tire.


CAUTION
Never counteract excessive pressure build-up in a hot tire by bleeding off air pressure (letting some air out). This will only further raise the tire operating temperature. It is best under these circumstances to let the tire cool the next time you stop, then bleed off the pressure.

Before starting on a long trip with lots of luggage, add about 2 to 4 psi to the tires to make them run cooler, but never exceed the maximum inflation pressure marked on the side of the tire.

Care For Special Wheels

Aluminum wheels should be cleaned and waxed regularly. Do not use abrasive cleaners because they may damage the protective coating.

 
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