Steering Geometry and Front Tire Wear Characteristics.
1. Users of the CCE-IHC 20 Ton Dump Truck, F50 70, -have been complaining about excessive front tire wear and the
accompanying low tread mileage. The CCE-IHC Dumper is equipped with a heavy 18,000 pound, Model FL 901 Rockwell
Standard front axle, riding on 16.5 by 22.5, wide base, .traction lug tires. Twin, frame mounted, Sheppard power steering
gear boxes are used for steering. Because of the construction truck design having the set-back front axle, the weight
imposed on the front axle always remains relatively high. The front axle weight varies between 13,000 pounds at curb
weight-to 18,000 pounds at maximum gross vehicle weight rating (GVWR). As a result, the front axle design is a series of
compromises. The space taken up by hub bearings and brakes prevents the kingpins from being ideally located. The
angles between the spindle, the steering arm, and the tie rod are all compromised from the ideal Ackermann steering set-
up. The wide base tires, the high loadings, and the steering geometry cause the inside front tire to scuff during turns from
side-slipping. Then, while turning, the weight of the truck transfers from the inner tire to the outer tire. As a result, the
tread of the inside tire is worn off at a high rate. The sharper the turn or the greater the speed, the greater the tire wear.
In addition, there are only 2-tires at the front giving directional guidance., to the 8-tires aimed straight ahead in the rear.
The on-off-road features of the rear tandem also contribute to front tire wear. When the truck rounds a corner, the outer
rear dual tandem tires free-wheel, while the inner rear dual tandem tires provide all the tractive effort to propel the truck.
This is due to the ratcheting effect of the Detroit No-Spin, traction-type differentials in both the front and the rear tandem
axles. As a result, the rear dual tandem provides a lot of resistance to steering around corners and both front tires see
this in the form of wear. The wide base, traction lug tires provide both floation and improved steering traction for off-road
operations. These tires carry heavy loads at a lower air pressure inflation. They provide the driver a much safer, less
fatiguing ride and impart less shock and vibration to the truck.
2. Good front tire mileage, as obtained with highway trucks, cannot be achieved with a good, on-off road dump truck.
Considering the on-off road features, front tire mileage of 8,000 to 25,000 miles is a normal range-for this type of heavy
truck. Individual truck tire tread life depends, of course, on actual use and will vary widely.
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