Feature Article: Seven tire killers
CURBING IN TIGHT QUARTERS. Curbing the tire in city environments can be avoided by remembering to swing wide enough to the left on right turns so the shorter wheelbase of the tractor doesn’t cause the trailer tires to roll over the curb. The longer the trailer, the wider you need to swing.
IMPROPER RETREADING. Retreading is best done by a shop that has sophisticated casing inspection equipment and well-trained inspectors. Every step of the process, whether installing a hot cap or pre-cured new tread, must be precisely controlled and verifiable. If possible, find customers of any given retreader and ask about their experiences with the tires.
TOE. Toe or toe-in refers to the angle between the front wheels when viewed from above. The tires normally are slightly closer together in front when at rest to compensate for rolling resistance.
CAMBER. Wheels are set almost vertically, but given a slight camber angle to make steering more stable by helping keep the tread flat on the road when the cab leans in corners. This setting is normally designed into the front axle.
CASTER. This is the angle of the kingpins from vertical. Proper caster helps ensure stability by generating a force that tends to return the steering to the straight-ahead position.
STEERING AXIS INCLINATION. The need for the outer tire to turn to a sharper angle than the inner tire when the truck is turning. This helps avoid scrubbing.
PERPENDICULARITY OF AXLE. Having the axle at exactly ninety degrees to the tractor or trailer chassis centerline so that it will roll straight rather than generating a side force.
Overloading a tire produces problems similar to those of underinflation, says Doug Jones, Michelin’s customer engineering support manager. Never load a tire beyond its rating.