🎓 Lesson 11
D5
Operating Cost Drivers: Fuel, Tires, Maintenance & Labor
Operating cost drivers are the main things that make hauling trucks and equipment expensive to run—like fuel, tires, repairs, and workers’ pay.
🎯 Learning Objectives
- ✓ Calculate hourly operating cost per truck using fuel, tire, maintenance, and labor inputs
- ✓ Analyze trade-offs between tire selection (e.g., bias vs. radial) and total cost of ownership over a 12-month haul cycle
- ✓ Design a preventive maintenance schedule aligned with OEM recommendations and site-specific duty cycles
- ✓ Explain how payload optimization impacts fuel consumption and tire life using empirical scaling relationships
- ✓ Apply labor cost multipliers for shift differentials, hazard pay, and training overhead in budget forecasting
📖 Why This Matters
In open-pit mines, haulage accounts for 30–50% of total operating costs—and up to 70% of mobile equipment expenses. A 5% reduction in fuel or tire cost per ton can improve net operating margin by $1M+ annually on a 50-Mtpa operation. Understanding what drives these costs—not just tracking them—is essential to designing efficient fleets, selecting appropriate equipment, and negotiating service contracts.
📘 Core Principles
Fuel cost is governed by engine efficiency, load factor, road grade, and idle time—each modifiable via dispatch logic and road design. Tire cost depends on rolling resistance, heat buildup, cut/chip damage, and inflation pressure; radial tires reduce heat but increase sensitivity to underinflation. Maintenance includes both time-based (oil changes, greasing) and condition-based (brake wear, driveline vibration) activities—driven by hours-in-service, km-traveled, and payload-cycles. Labor cost extends beyond base wages to include statutory benefits, shift premiums, safety training, and crew supervision ratios—all regulated by jurisdiction and collective agreements.
📐 Hourly Operating Cost (HOC)
The Hourly Operating Cost model aggregates major variable expenses into a single metric for fleet comparison and dispatch optimization. It enables apples-to-apples evaluation across equipment types and duty cycles.
Hourly Operating Cost (HOC)
HOC = (C_fuel + C_tires + C_maint + C_labor) / H_operatingTotal annual variable cost divided by annual operating hours to determine cost per hour of equipment availability.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| C_fuel | Annual fuel cost | USD | Total diesel or LNG cost consumed in one year |
| C_tires | Annual tire cost | USD | Cost of replacement tires plus mounting/balance labor |
| C_maint | Annual maintenance cost | USD | Parts, labor, and consumables for scheduled and unscheduled repairs |
| C_labor | Annual labor cost | USD | Wages, benefits, premiums, and supervision for assigned operators/maintainers |
| H_operating | Annual operating hours | hr | Total productive and standby hours logged by equipment |
Typical Ranges:
220-t articulated truck, moderate duty: $240 – $310/hr
360-t rigid frame truck, high-dust, steep grade: $340 – $420/hr
💡 Worked Example
Problem: A 220-ton articulated dump truck operates 5,200 hours/year. Annual fuel use = 280,000 L at $1.45/L; tire cost = $192,000 (4 sets @ $48,000/set); scheduled maintenance = $165,000; labor (2 operators × $125/hr × 2 shifts × 2,600 hrs) = $650,000. Calculate HOC.
1.
Step 1: Compute annual fuel cost = 280,000 L × $1.45/L = $406,000
2.
Step 2: Sum all annual costs = $406,000 (fuel) + $192,000 (tires) + $165,000 (maintenance) + $650,000 (labor) = $1,413,000
3.
Step 3: Divide by annual operating hours = $1,413,000 ÷ 5,200 hrs = $271.73/hr
Answer:
The result is $271.73/hr, which falls within the safe range of $240–$310/hr for 200–240 t class articulated trucks in moderate-duty applications.
🏗️ Real-World Application
At Rio Tinto’s Pilbara iron ore operations, a 2022 fleet optimization study replaced 12% of bias-ply tires with radial alternatives and adjusted inflation pressures based on payload telemetry. Combined with GPS-guided idle-reduction protocols, this reduced average HOC by $18.40/hr—yielding $4.3M annual savings across 210 trucks without compromising availability or safety KPIs. Tire life increased from 7,800 to 10,200 hours, while fuel consumption dropped 4.2% due to lower rolling resistance.
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