Gross machine operating weights have been frequently misapplied on off-highway trucks in the market place. For example, maximum, which means, “not to exceed”, has been inappropriately used as the target. Regulatory and product support considerations have prompted some dealers and customers to request quantification of “acceptable” payloads on Caterpillar’s Mining Trucks. Technically, the correct answer is that any overload will adversely affect component life and potentially affect steering & braking performance. If the overloading is severe enough, the truck will be unsafe to operate. The following is intended to communicate guidelines of the 10/10/20 policy, the relationship between payload and performance, and the maximum operating weights and the associated payload policy that Caterpillar is using in support of warranty considerations and maintenance and repair contracts (MARC's) for Mining Trucks.
Caterpillar’s payload overload policy, referred to as the “10/10/20” policy, states that “The mean (average) of the payload distribution shall not exceed the target payload and no more than 10% of payloads may exceed 1.1 times the truck target payload and no single payload shall ever exceed 1.2 times the target payload.”
KEY ISSUES:
1. Target payloads for various Caterpillar truck models, when equipped with different truck body configurations are outlined in the Table 1 at the end of this document. Site conditions may dictate that underloading is more economical than loading at the target payload.
2. Gross machine operating weights and associated payloads are continually being updated. For the latest approved mining truck gross operating weights with the target and maximum payload visit: https://mining.cat.com/products/trucks.html
3. Actions required to maintain brake certification to SAE & ISO standards and British Columbia (B.C.) codes are addressed.
4. Component life is directly related to gross machine weight and associated payload. Therefore, specific support commitments will be required from Caterpillar and it’s dealers for given applications.
5. In this policy, target payload is the difference between gross machine operating weight and empty operating weight. The mean (average) payload distribution shall not exceed the target payload. Reducing empty operating weight provides for increased payload capacity, and an increase in empty machine weight decreases payload capacity. Empty operating weight includes bare chassis plus 4% for normal debris accumulation and full fuel.
6. This policy is applicable to current production models with the latest power train and structural improvements and non-current products updated to the latest improvements. The power train improvements required under the 10/10/20 overload policy are outlined at the end of this document.
PAYLOAD DISTRIBUTION
Target payload is defined as 100%. The target should always be 100. Caterpillar's 10/10/20 policy allows for no more than 10% of the loads to fall in the 110% to 120% range (yellow region). No loads should ever exceed the trucks steering and braking certification. Exceeding the steering and braking certification would make the truck unsafe to operate.
Target payload is defined as 100%. The target should always be 100. Caterpillar's 10/10/20 policy allows for no more than 10% of the loads to fall in the 110% to 120% range (yellow region). No loads should ever exceed the trucks steering and braking certification. Exceeding the steering and braking certification would make the truck unsafe to operate.
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| Payload Distribution |
COMPONENT LIFE vs. PAYLOAD
demonstrates that the component life is decreased significantly when overloaded 10% to 20%. The rate at which component life decreases as a result of overloading is greater than the rate at which component life increases as a result of underloading.
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| Component Life vs. Payload |
There are a few basic rules of thumb related to component life vs. payload. First, engine life is directly related to fuel burn. If payload is increased, the truck gets heavier creating a higher duty cycle resulting in greater fuel burn and shorter life. The torque converter and transmission life are related to torque and again as payload is increased the truck gets heavier. More torque is required to move a heavier truck resulting in shorter torque converter and transmission life. The lower powertrain life is related to load and speed. A heavier truck puts more load on the lower powertrain and again the results is a decrease in component life.
PLACEMENT OF PAYLOAD
Not only is component life impacted by the amount of payload, but it is also impacted by the placement of the payload. A decrease in component life will occur from improper load placement. Specifically, there are three types of improper load placement, load shifted towards the front, load shifted towards the rear, and load shifted towards the side. All three types of improper load placement negatively impact frame and body life. If the load is shifted towards the front, the front brakes, bearings, front tires, steering, hydraulic hoist, body rest pads, and body canopy will be negatively impacted. Trucks with correct load placement and incorrect load placement with the load shifted towards the front.
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| Side View of Load Placement |
If the load is shifted towards the rear, the final drive and rear tires will be negatively impacted. Furthermore, the payload will become unstable and dribble off the back of the body. Trucks with correct load placement and incorrect load placement with the load shifted towards the rear.
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| Side View of Load Placement |
If the load is shifted towards the side, the final drive, bearings, hoist cylinders, and pivot bore areas will be negatively impacted. Trucks with correct load placement and incorrect load placement with the load shifted towards the side.
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| Rear View of Load Placement |
777D & 793C
Note that modification to brake service procedures is required to maintain certification on 777D and 793C models. Specifically, the brakes must be rebuilt at 75% brake wear to ensure that the parking brake will hold in grade per ISO, SAE, braking codes. A measurement instruction has been issued in conjunction with this overload policy. This action enables the brakes to be certified to SAE and ISO standards at up to 1.2 times target payload.
TIRES AND RIMS
It is recommended that users of this policy contact their tire supplier and rim supplier, if other than Caterpillar, to discuss application, site conditions, haul roads, and allowable tire loads before adopting this policy.
TARGET AND MAXIMUM PAYLOADS BY MODEL
The following table is for a representative vehicle configuration. All weights are dependent on chassis configuration, fuel tank, body type, tires, and optional equipment selected.
Overload is a major factor in life shortfalls of planned component replacement goals. Haul road conditions, machine maintenance, and operation techniques are also significant factors.
POWER TRAIN IMPROVEMENTS REQUIRED UNDER OVERLOAD POLICY
797A Mining Truck
• Depending upon the serial number and configuration, existing 797A’s have an overload policy ranging from 10/10/11 to 10/10/20. Most customers with 797A’s have the option to upgrade to 59/80R63 tires so long as other changes are made to the chassis. For information about changes to 797A’s that impact payload and the overload policy contact a mining truckmarketing representative in Decatur.
793 Mining Truck
• Larger wheel bearings – production 10/96
• 20mm wrapper on fabricated wheel – production 1/96
• RAX filtration – production 7/95 (cost to add already paid by Caterpillar)
• Differential ring gear shroud – production 7/95
• Wheel bearing preload adjustment – production 12/97
789 Mining Truck
• Cast wheel with larger wheel bearing – production 10/97
• Differential ring gear shroud – production 11/95
785 Mining Truck
• Cast wheel with larger wheel bearing – production 3/97
• Differential ring gear shroud – production 12/95
• Enlarged wheel bearing retainer holes – screens removed – production 3/98
