Chicagoland MG Club: Tech Tips

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Tire Myth Exploded!

Like John Twist, I grew up with a strong and unwavering belief in the commandment: "Thou shalt not cross-rotate radial tires, nor cause reversal of their directional rotation". A friend of mine even carried two used spare tires (couldn't afford new ones in those days) in his Fiat - one which had been run on the left side of the car, and one on the right. He wasn't going to risk having a tire fly apart because he broke the rules!

Thus, my initial reaction to Mr. Kraft's letter was disbelief, followed by curiosity. Do $500 truck and bus tires live by different rules than our relatively tiny and inexpensive sports car tires? Have two generations of drivers spent their automotive lives believing in tire fables?

Coker Tire Co., Firestone, The Kelly-Springfield Tire Co., and Pirelli Armstrong Tire Corp. responded to my plea for authoritative commentary with a unanimous "It's OK to cross-rotate radial tires, with the exception of 'Temporary Use Only' spares, and tires with uni-directional tread patterns". Firestone added the recommendation that the vehicle manufacturer's instructions be followed, even though their tires can be cross-rotated. Our thanks to these companies for all the information they sent, and special thanks to Mr. Jim Hildebrand of Coker Tire Co. who added: "I understand that the original theory (common to the late '60s) was that, particularly on the drive tires, the torque would cause the radial side wall cords to slant, and if rolling direction was changed that a balance problem might exist. Further research and testing disproved this theory. The basis being that a slanting of the side wall cords did not actually take place."

Approved Rotation Patterns

(extracted from information supplied by Pirelli Armstrong)

The purpose of regularly rotating tires is to achieve more uniform wear for all tires on a vehicle. Before rotating tires, individual owner's manuals should always be consulted for rotation recommendations for specific vehicles. If no rotation period is specified, tires should be rotated every 6000 to 8000 miles or at any sign of uneven wear. The first rotation is most important.

If the tires show uneven wear, ask the service person to check for and correct any misalignment, imbalance, or other mechanical problem before rotation.

Car & Light Truck Tire Rotation Patterns

Do not include a "temporary use only" spare tire in any of these rotation patterns. If the vehicle owner has a regular tire as a spare and wishes to include it in the tire rotation process, the proper procedure is as follows:

Use one of the four tire rotation patterns, but insert the spare in the right rear position, and place the tire which would have gone to the right rear position in the trunk as the new spare.

When tires are rotated, inflation pressures must be adjusted in accordance with the vehicle manufacturer's recommendations.

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