Case Study 2: Limestone Quarry Fleet Standardization in Central Texas

Scenario

A family-owned limestone quarry near Austin, TX, operated three aging Volvo A40E articulated haulers and planned to add two new units. With inconsistent tire sourcing (mix of bias and radial, multiple sizes), maintenance costs were volatile and safety audits flagged uneven wear patterns. Constraints included budget limitations (no capital for road regrading), reliance on local tire vendors (limited stock of >50″ sizes), and need for cross-truck compatibility to simplify inventory and training.

Given Data

• Payload: 42 tons (A40E rated capacity; actual average loaded weight)
• Road Gradient: 3.1% (mild but with frequent tight turns and potholes)
• Cycle Time: 6.8 minutes
• Distance Traveled per Cycle: 2.4 km
• Tire Wear Factor: 0.032 km/ton (low abrasivity of weathered limestone, but high cut/chip risk from uncrushed oversize)

Calculation

The selector uses a derated sizing algorithm for articulated trucks with dynamic cornering loads:

1. Base Tire Size Index (TSI) = 9.2 × √(Payload × (1 + 0.05 × Road Gradient))
   = 9.2 × √(42 × (1 + 0.05 × 3.1)) = 9.2 × √(42 × 1.155) = 9.2 × √48.51 ≈ 9.2 × 6.965 = 64.1

2. Maneuverability Penalty = 2.3 × (Cycle Time / 10) × (Distance Traveled / 5)²
   = 2.3 × (0.68) × (0.48)² = 2.3 × 0.68 × 0.2304 ≈ 0.36

3. Wear-Compensated Size = TSI × (1 − 0.25 × (0.05 − Tire Wear Factor))
   = 64.1 × (1 − 0.25 × (0.05 − 0.032)) = 64.1 × (1 − 0.25 × 0.018) = 64.1 × 0.9955 ≈ 63.8

4. Final Recommended Tire Size = round(64.1 + 0.36 − 0.2) = 64.3 inches (standardized to 26.5R25 radial—common in regional dealer inventory)

5. Estimated Tire Life = (10,000 × 60) / (Payload × Distance Traveled × Tire Wear Factor × 0.92)
   (0.92 correction for lower-speed, high-cornering stress reducing thermal load)
   = 600,000 / (42 × 2.4 × 0.032 × 0.92) = 600,000 / (2.97) ≈ 202,020 hours (Note: This reflects cumulative life across all tires per truck; per-tire life is 202,020 / 6 ≈ 33,670 hours — consistent with field data)

Result and Decision

The tool recommended 26.5R25 tires (64.3″). The quarry standardized on the Titan RT55 radial with cut-resistant tread compound. After 18 months, average per-tire life reached 34,100 hours (±1,200), exceeding prior best of 28,500. Inventory carrying cost dropped 63%, and operator-reported handling stability improved markedly in wet conditions.

Lesson

For smaller fleets with mixed-age equipment, prioritizing vendor-local availability and service support over theoretical 'optimal' size often delivers greater ROI—especially when the tool’s recommendation falls within ±2 inches of a widely stocked standard size.