How to Size a Haul Truck Fleet
Fleet sizing is four multiplications and one rounding rule — and operations lose millions annually by fumbling the rounding rule. Here's the clean method, plus the loader-match check most first passes skip.
01Build the cycle time honestly
Cycle = load + haul + dump + return + spot/queue. Example: 3 + 8 + 1 + 5 + 1 = 18 minutes. Haul and return come from the actual profile — distance, grade, and rimpull curves, not hope. Steal times from your fleet-management system if you have one; it doesn't flatter anybody.
02Convert to real productivity
Trucks don't get 60-minute hours. Apply an effective hour (45–52 min is honest): trips/hr = 50 ÷ 18 = 2.78. At 100-ton payload: 278 tph per truck. Payload means measured payload — carryback, poor fill factors, and light material quietly shave 5–10%.
03Divide demand and round UP
Need 1,500 tph: 1,500 ÷ 278 = 5.4 trucks → 6. Always the ceiling, never the nearest: 5 trucks delivers 1,390 tph and a permanent 7% shortfall that shows up as overtime, missed ships, and a very unhappy plant. Fractional trucks don't exist; shortfalls do.
04Check the match factor
MF = (trucks × loader cycle per pass × passes) ÷ truck cycle — or more simply, compare loader capacity to fleet demand. MF near 1.0 balances the system; below ~0.85 the loader starves and waits; above ~1.15 trucks queue and burn idle fuel. If six trucks push MF to 1.3, the answer might be a bigger loader, not more trucks.
05Add availability, then re-round
Mechanical availability of 85–90% means the calculated fleet is the operating fleet, and the owned fleet = operating ÷ availability. Six operating at 88% → 6.8 → 7 owned. Yes, round up again. The seventh truck is cheaper than the down-shift it prevents.
06Sanity-check with cost per ton
Total hourly ownership + operating cost ÷ delivered tph = haul cost per ton. If a design change (shorter ramp, better road, bigger truck) beats adding a unit on $/ton, buy the design change. Fleets are sized in trucks and judged in dollars.
Feel the queueing pain interactively in Grade Runner and the Sim Yard — or have ShotRock run the real analysis with your cycle data.
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