Dump truck cycle time: how to calculate fleet size before you buy

Most dump truck purchases are sized on payload alone, and most of those sites end up with the wrong fleet. Payload tells you what one truck can carry per trip. It tells you nothing about how many trips a day the truck can complete, and trips per day is the number that decides whether the haul matches the loading equipment.

This guide sets out the calculation the way a fleet planner does it: cycle time first, then trips per hour, then the truck count that keeps the loader busy without building a queue.

The four variables that decide cycle time

Haul cycle time is the round trip a truck makes, from the moment it is loaded to the moment it is ready to be loaded again. It breaks into four parts.

Phase	What it includes	Driven by
Loading	Positioning, filling the body, spotting	Loader capacity vs body volume, material density
Haul (loaded)	Travel from loading face to dump point	Distance, gradient, surface condition, speed limit
Dump and manoeuvre	Reversing, tipping, pulling away	Dump point layout, turning radius, traffic
Return (empty)	Travel back to the face	Same route, faster because empty

Loading time is the one operators most often get wrong. It is not the time the loader takes to fill one bucket; it is the number of passes required to reach the target payload, multiplied by the pass time. If the body volume and the material density mean the truck reaches its payload limit before the body is full, the extra passes stop paying for themselves, and the truck leaves the face part-loaded at full weight. That is a specification mismatch, not a driving problem, and no amount of operator skill fixes it.

From cycle time to trips per hour

Trips per hour is 60 divided by cycle time in minutes. That result is the theoretical maximum, and it is always optimistic. Two adjustments bring it back to reality:

1. Efficiency factor. Gradients, soft ground, junctions, weather and shift changes all consume time that a clean cycle calculation ignores. Planners typically apply an efficiency factor well below 1.0 rather than treating the theoretical figure as achievable.
2. Queueing loss. If more trucks arrive at the loader than it can service, the surplus waits. Waiting trucks still burn fuel and operator hours while producing nothing.

The practical consequence is that adding trucks has diminishing returns well before it has no returns at all. Past a certain point every extra truck spends most of its shift in a queue.

Worked example (illustrative figures)

The arithmetic below uses round numbers to show the method. They are not quotations and not a specification for any machine.

Assume a one-way haul of 5 km, an average loaded speed of 20 km/h and an empty return at 30 km/h.

Component	Calculation	Minutes
Haul loaded	5 km at 20 km/h	15.0
Return empty	5 km at 30 km/h	10.0
Dump and manoeuvre	Fixed allowance	2.0
Loading	5 passes at 0.9 min	4.5
Cycle time		31.5

At 31.5 minutes the theoretical rate is about 1.9 trips per hour. Apply a 0.8 efficiency factor and the planning figure is roughly 1.5 trips per hour.

If one truck completes 1.5 trips per hour at a working payload, the site’s required haul rate divided by that figure gives the truck count. The reverse calculation tells you whether the loader is the constraint: if the loader can fill a truck in 4.5 minutes, it can service roughly 13 trucks per hour, which is far more than the haul can deliver. In that configuration the haul is the bottleneck and extra loaders are wasted money.

Run the same calculation with a 1 km haul and the picture inverts: cycle time collapses, the loader becomes the constraint, and the answer is a bigger loader rather than more trucks.

What to send a supplier so the quote is usable

Suppliers cannot choose a truck for you without the numbers above. A quote built on “we need some dump trucks for a quarry” will be either over-specified or under-specified, and you will discover which only after delivery.

Send these six items and the reply becomes comparable between suppliers:

1. Material type, loose density and maximum fragment size
2. One-way haul distance and route gradient
3. Road surface and condition (sealed, gravel, haul road)
4. Required tonnes per shift or per day
5. Loading equipment available, with bucket or bucket capacity
6. Dump point layout and any access restrictions

If the body volume and payload class cannot both be satisfied with one model, that is a real engineering trade-off and the supplier should say so. A supplier who quotes without asking any of the six is quoting a catalogue page, not a solution.

Our inquiry checklist expands these six points into the full set of questions worth settling before any price is discussed, and the payload sizing guide covers the body-volume-to-tonnage conversion in detail. For quarry-specific constraints, see machine selection for quarry and mining work. If you want a configuration reviewed against your own numbers, send the six items through the inquiry form and we will work through them with you.

Common sizing mistakes

Matching trucks to trucks. Buying a fleet of identical trucks because the first one worked is not fleet planning. Different haul legs, different materials and different dump points may each want a different answer.

Ignoring the return leg. An empty truck is faster, but not infinitely faster, and on a soft haul road the loaded and empty speeds converge. Use measured speeds, not brochure figures.

Treating payload as a constant. Payload is capped by both body volume and axle loading, and which cap binds depends on material density. Wet material can hit the weight cap at two-thirds of the body volume. This is why the same truck carries visibly different loads on different sites.

Skipping the queueing check. A fleet plan that ignores queueing will look efficient on paper and lose a third of its capacity in the yard. Model the loader’s service rate alongside the haul rate; whichever is lower sets the site’s throughput.

Sizing for peak, not average. Peak demand is real, but a fleet bought for the peak sits idle the rest of the year. Where the peak is short, rented capacity usually beats owned capacity.

Summary

Fleet size follows from cycle time, not from payload. Cycle time follows from four phases, of which loading is the one most often miscalculated. Apply an efficiency factor, check the loader’s service rate against the haul rate, and the correct truck count falls out of arithmetic rather than intuition.

The numbers in any fleet plan are only as good as the input data. Where a figure is unknown — measured haul speeds, actual material density, real gradient — measure it before committing to a purchase, and treat any supplier quote that arrives without those questions as provisional.