Camber, measured in degrees, is the amount the wheel is
tilted at its top, in or out, from a vertical position. Outward tilt of the wheel is positive camber;
inward tilt is negative. Originally,
trucks were designed with a small positive camber. In such a design, the load could be more
effectively placed on the heavier inner wheel bearing, and a negative camber
was avoided as axles sagged and parts wore as a result of normal
operation. It also reduced side thrust
on the kingpin. The amount of camber has
been decreased considerably on trucks over the past few decades because
stronger axle materials have become available and suspension designs have been
improved as well as the introduction of radial tires.
Along with the introduction of more powerful engines came
signs of abnormal tire wear. Right front
tires have been found to cup and wear on the outer edge. The cause of this is a combination of
positive camber and the effects of increased engine torque.
The engine’s crankshaft rotates counter-clockwise when
viewed from the driver’s seat. The
torque reaction on a heavy duty truck can transfer up to 2,000 lbs. from the
left front wheel to the right when starting out. When this transfer takes place, the
centerline of the tire will offset from the centerline of the rim by as much as
¾ of an inch. After the vehicle gets up
to speed in low gear, there is an instantaneous release of torque at the moment
the clutch is disengaged snapping the tire back and bringing the two
centerlines together once again. This
snap-back is the cause of the cupping on the outside of the right front tire.
Adjustment to correct camber specifications requires setting
the right front wheel at -1/8° camber – straight up and down. In this way the tire will be planted square
on the road when it’s torque loaded. The
left front wheel should be set at -1/4° positive camber. These settings will provide maximum tire life
and better drivability.
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| Dis-similar Camber Correction (To Decrease Right & Increase Left) |
To make a camber adjustment, the axle is fitted with clevises
on both the right and left sides – left side outside the spring seat, right
side inside the spring seat. A hydraulic
ram is then used between the clevises, physically correcting the axle to the desired
camber settings. Another ram is then
placed outside the right clevis to reduce the camber in the right wheel. Never spot-heat an axle in order to correct
it; high temperature will remove the strength it was given by heat treatment.
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