Case Study 1: Copper Mine Haul Fleet Optimization in Northern Chile

Scenario

A Tier-1 copper mining operation in the Atacama Desert (elevation ~3,200 m) expanded its open-pit fleet to support increased throughput. The site features steep haul roads (up to 12% gradient in sections), abrasive volcanic rock surfaces, and extreme diurnal temperature swings (−5°C to 35°C). Key constraints included minimizing unscheduled tire replacements (which cause >$12k/hr downtime), adhering to OEM axle load limits, and avoiding oversizing tires that would reduce payload efficiency due to excessive rolling resistance.

Given Data

• Payload: 135 tons
• Road Gradient: 8.2%
• Cycle Time: 14.5 minutes
• Distance Traveled per Cycle: 7.3 km
• Tire Wear Factor: 0.068 km/ton (elevated due to sharp, angular waste rock and poor road surface maintenance)

Calculation

The Haul Truck Tire Selector applies a weighted sizing model combining mechanical stress and thermal wear:

1. Base Tire Size Index (TSI) = 12.5 × √(Payload × (1 + 0.12 × Road Gradient))
   = 12.5 × √(135 × (1 + 0.12 × 8.2))
   = 12.5 × √(135 × 1.984)
   = 12.5 × √267.84 ≈ 12.5 × 16.37 = 204.6 inches

2. Cycle-Distance Adjustment = 0.8 × (Distance Traveled / 5) × (Cycle Time / 10)
   = 0.8 × (7.3 / 5) × (14.5 / 10) = 0.8 × 1.46 × 1.45 ≈ 1.69

3. Wear-Compensated Size = TSI × (1 + 0.3 × (Tire Wear Factor − 0.05))
   = 204.6 × (1 + 0.3 × (0.068 − 0.05)) = 204.6 × (1 + 0.3 × 0.018) = 204.6 × 1.0054 ≈ 205.7 inches

4. Final Recommended Tire Size = round(204.6 + 1.69 + 0.7) = 207.0 inches (nearest standard size: 53/80R63)

5. Estimated Tire Life = (10,000 × 60) / (Payload × Distance Traveled × Tire Wear Factor × 1.15)
   (1.15 accounts for altitude-induced reduced cooling & thermal degradation)
   = 600,000 / (135 × 7.3 × 0.068 × 1.15)
   = 600,000 / (76.35) ≈ 7,858 hours

Result and Decision

The tool recommended a 53/80R63 ultra-deep-tread radial tire (207.0″ nominal diameter). The mine procurement team selected the Bridgestone M845 ECO with reinforced sidewall and heat-resistant compound—validated via 3-month pilot on two CAT 797F trucks. Mean time between replacements increased from 5,200 to 7,640 hours (±3.2%), aligning closely with the estimate. Tire-related downtime dropped by 41%.

Lesson

Altitude and surface abrasivity significantly accelerate thermal fatigue—not just mechanical wear—so tire wear factor must be calibrated in situ using historical failure mode data, not just generic supplier tables.