Issue link: http://read.dmtmag.com/i/34501
CAMBER Camber is the angle formed by the inward or outward tilt of the wheel referenced to a vertical line. Ideal camber may vary in different applications and in different axle positions as affected by load distribution (i.e. front axle variance of 6,000 to 12,000 pounds, drive axle range of 8,000 to 17,000 pounds, and trailer axle range of 4,000 to 20,000 pounds). • Camber is positive when the wheel is tilted outward at the top. • Camber is negative when the wheel is tilted inward at the top. • Excessive positive camber may cause smooth wear on the outer half of the tire tread. • Excessive negative camber may cause wear on the inner half of the tread. • Camber only causes a noticeable “pull” if on the steer axle the right and left wheel camber angles are not very close in magnitude (greater than 1⁄2 degree). • Negative camber can also be a cause of inside shoulder wear on trailer axle in dual or single configuration. • A free-rolling tire is more sensitive to camber than a tire twisting or turning under the effect of torque. • A wide tire with a relatively low aspect ratio is more sensitive to camber than a narrow high aspect ratio tire. • Generally, the vehicle will pull to the side with the most amount of positive camber. Camber is often a contributor to wear occurring on the interior ribs/blocks of the inner dual drive tires and can sometimes affect the interior ribs/blocks of the outer dual as well. Steer position: Steer axles (which are generally, but not always, a forged axle) are designed with static unloaded positive camber and tend to produce better tire wear when provided with slightly negative camber due to the effects of cornering forces, load transfer, and steering Ackerman geometry, which tend to stress and produce outside shoulder wear during turning maneuvers. In the interest of more even overall wear, it is therefore advantageous to let the wear be biased toward the inside shoulder (via slightly negative camber) during straight ahead driving. Drive position: Generally, camber is not a major contributor to drive axle irregular wear, although combined with dual position toe-in or toe-out may cause the onset of a wear pattern. Trailer position: Trailer axles are typically fabricated from steel tubing with spindles welded to the ends. They are usually built straight, so there will be some negative camber induced when installed under a trailer. Additional loading of the trailer will cause additional negative camber. Most trailer axles deflect to about -0.5 degree camber at 17,000 pounds per axle loading. Camber can accelerate shoulder wear on dual or single tires. Higher degrees of negative camber will show up on the inner shoulder, and positive camber on the outer shoulder. Wide single tires seem more susceptible to camber induced wear. Camber correction by bending axles is NOT RECOMMENDED by axle manufactures, nor endorsed by Michelin ® . Consult the axle manufacturer if camber is found to be incorrect (outside manufacturer specification). CASTER Positive (+) caster is the backward tilt at the top of the kingpin when viewed from the side. Negative (-) caster is the forward tilt at the top of the kingpin when viewed from the side. The purpose of caster is to provide self-aligning forces on the steer tires to stabilize the vehicle when driving straight down the road under braking, free wheeling, and power conditions. Insufficient caster reduces stability and can cause wander. Excessive caster increases steering effort and can cause shimmy. Either of these conditions may also have a detrimental effect on tire wear. Excessive caster beyond the vehicle manufacturer’s specification may result in induced camber causing excessive tire wear, particularly fleets that are in local and regional operations. Caster is adjustable with shims. Adjusting only one side is not recommended. Caster on both sides should be equal or not more than 1⁄2 degree difference. Generally, the vehicle will pull to the side with the least amount of positive caster. Positive Camber Positive Caster + 0° 48 Section Three: Extending Tire Life - Negative Caster