Ramp Truck Speed vs Grade Calculator
A truck climbing a ramp must overcome two resistances: grade resistance (from gravity acting along the slope) and rolling resistance (tyre and surface losses).
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the loaded gross vehicle weight (GVW) in tonnes, the ramp grade as a percent (a 1-in-12.5 ramp is 8%), the rolling resistance percent for the haul-road surface (typically 2-4% when well maintained), and the usable power delivered at the wheels in kW.
- Read the achievable steady speed in km/h, plus the total resistance and the rimpull force the truck must produce to hold that speed.
- Compare the result to the OEM rimpull-vs-speed / retarder chart for the exact truck model to confirm it can actually deliver that force at that speed.
How it works
A truck climbing a ramp must overcome two resistances: grade resistance (from gravity acting along the slope) and rolling resistance (tyre and surface losses). For typical haul-road grades under about 10% the small-angle approximation sin ~ tan holds, so each is force (N) = GVW (t) x 1000 x 9.81 x (resistance% / 100). Adding them gives the total rimpull force the driveline must deliver: F = GVW x 1000 x 9.81 x (grade% + rolling%) / 100.
At steady speed, mechanical power equals force times velocity, so P (W) = F (N) x v (m/s), which rearranges to v = P / F. The tool converts usable power from kW to W, divides by the required rimpull force to get m/s, then multiplies by 3.6 for km/h. This is a power-limited ceiling: it assumes all usable power reaches the wheels and ignores gearing steps, torque-converter and retarder behaviour, wheel-slip traction limits, air and inertia. The real truck follows a stepped rimpull-vs-speed curve and is usually a little slower.
Worked example
220 t truck on an 8% ramp. A haul truck with a gross vehicle weight of 220 t climbs a ramp at 8% grade with 3% rolling resistance, delivering 1,200 kW usable power at the wheels. Total resistance = 8 + 3 = 11%. Rimpull force required = 220 x 1000 x 9.81 x 0.11 = 237,402 N = 237.4 kN. Achievable steady speed = 1,200,000 W / 237,402 N = 5.05 m/s = 18.2 km/h. This is a power-limited ceiling; the real truck may be slower once gearing and traction limits are applied.
Common mistakes
- Confusing grade in degrees with grade in percent. This tool expects percent (rise over run x 100). An 8% grade is about 4.57 degrees, not 8 degrees.
- Entering flywheel/rated engine power instead of usable power at the wheels. Driveline, accessory and efficiency losses mean wheel power is lower, so using rated power overstates the achievable speed.
- Treating the answer as a guaranteed real-world speed. It is a power-limited ceiling that ignores gearing, traction and the truck's actual rimpull-vs-speed curve, so verify against the OEM chart.
Frequently asked questions
Why is the total resistance just grade plus rolling resistance?
Both are expressed as a percentage of the vehicle weight acting as a resisting force, so on a ramp they simply add. For small grades the gravity (grade) term uses sin ~ tan, so grade% + rolling% gives the effective total resistance the truck must overcome, and the rimpull force scales directly with it.
Does this include the truck's gears or traction limits?
No. It is a simplified power-limited steady-speed estimate: it assumes the usable power you enter is fully available at the wheels against the resistance. Real trucks shift through discrete gears and can be traction-limited (wheel slip) on loose or wet surfaces, so always compare with the manufacturer's rimpull-vs-speed chart.
What rolling resistance should I use?
On a well-maintained, hard, dry haul road, 2-3% is common; soft, rutted, wet or poorly maintained surfaces can be 4% or more. Rolling resistance is very sensitive to road condition, so use a value that reflects the actual surface, and check haul-road design references for your fleet.
Can I use it for a downhill (negative grade)?
Enter a negative grade for a downhill ramp, but this model only produces a meaningful power-limited speed when the total of grade plus rolling resistance stays positive (the truck is still fighting net resistance). On steeper descents the limiting factor is braking/retarder capacity, not engine power, so this tool does not apply and you must size the retarder from the OEM braking chart instead.
Related tools
- Truck Cycle Time Calculator
- Fleet Productivity Calculator
- Cost per Tonne Calculator
- Haul Road Grade Resistance Calculator
- Rolling Resistance Calculator
- Tonne-Kilometre (TKm) Cost Calculator
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