The Davis Dam Test: SAE J2807 Gradeability Explained

Arizona State Route 68 near Davis Dam is the reference route behind one of the best-known towing tests. SAE J2807's highway gradeability evaluation considers how a loaded tow vehicle performs on a sustained climb under defined conditions—a demanding test of both pulling performance and heat rejection.

The test is one part of a broader rating method, not a separate certification badge or a guarantee for every trailer. A Davis Dam grade profile can also be reproduced on a test dynamometer, so the name does not mean every truck is physically driven on the same Arizona road.

Why the Davis Dam climb matters

SAE's reporting describes the reference route as an 11.4-mile section of Arizona State Route 68 near the Colorado River, climbing above 3,000 feet and reaching grades of about 7%. That combination of sustained load, elevation gain, and heat makes it a useful example when explaining gradeability and cooling demand.

SAE Media's 2025 account of the test describes a starting temperature of 100°F (38°C) with the air conditioning at full capacity. These are test conditions reported for the standard—not instructions for everyday towing or a prediction of the temperature every vehicle will reach.

The route is also a reference profile, not necessarily a road trip every test vehicle must make. SAE's report on Ford's development testing describes a towing dynamometer that reproduces the Davis Dam grade profile on level ground. The applicable test procedure, not a simplified infographic, determines how a particular rating is evaluated.

What the highway-gradeability test evaluates

Sustained pulling ability: the vehicle must meet the procedure's gradeability performance at the relevant test weight.
Thermal performance: the powertrain and cooling systems operate under sustained load and defined environmental conditions.
Vehicle-category requirements: the procedure includes defined performance criteria, and speed thresholds can vary by vehicle category and standard revision. A single speed figure should not be applied to every truck or SUV.

A passing result helps support a manufacturer's rating under those defined conditions. It does not mean that the same vehicle can tow any trailer at that weight at any speed, on any grade, or in any weather.

A simplified elevation profile

The supplied profile illustrates the long uphill route and highlights a sustained grade. Its plotted elevations, shaded segment, minimum speed, and temperature notes are illustrative—not an official SAE route map or a universal set of pass/fail values.

Supplied illustration. Route and test labels are simplified; use the current SAE standard and vehicle maker's documentation for exact requirements.

Understanding the thermal-system graphic

Long climbs can place sustained demand on the engine, transmission, charge-air system, and cooling package. Engineers may instrument development vehicles to study those systems, but sensor locations, limits, and control strategies are specific to the vehicle.

A simplified thermal-system view highlights the way heat can move through an A/C condenser, charge-air cooler, transmission cooler, and engine radiator. These components may share airflow or exchange heat in different ways depending on the vehicle. Development teams can monitor coolant, transmission fluid, engine oil, exhaust, and other temperatures with vehicle-specific instrumentation; there is no single set of dashboard or telemetry numbers that applies to every tow rig.

Conceptual cutaway illustration of a tow vehicle climbing a hot-weather grade with engine cooling and telemetry callouts — Conceptual illustration, not recorded test data. The temperatures, boost pressure, warning zones, and other displayed readouts are not universal J2807 pass/fail limits or guidance for a specific vehicle.

Do not compare a dashboard reading with numbers from a generic graphic to decide whether a vehicle is safe to keep climbing. Follow the owner's manual and the vehicle's warning messages. If a warning appears, use the manufacturer's instructions and stop safely when directed.

What the Davis Dam test does not tell you

It is not the whole J2807 evaluation. SAE J2807 also establishes other performance criteria and rating calculations; the Davis Dam climb describes the gradeability part.
It is not a universal real-world guarantee. Trailer shape, speed, road grade, payload, cargo, and weather can change what a trip demands.
It does not erase other weight limits. Towing capacity, payload, GVWR, GCWR, axle ratings, tire limits, and hitch ratings all need to be checked for the loaded combination.
It does not make every configuration identical. Engine, drivetrain, axle, cab, options, and factory tow equipment can affect the rating for a particular model year.

How to apply the test to your own towing plans

Find the tow rating for the exact model year and configuration in the manufacturer's towing guide and owner's manual.
Check payload, GVWR, GCWR, front and rear GAWR, tires, receiver, and hitch limits—not just the maximum trailer-weight number.
Account for passengers, cargo, accessories, hitch hardware, and the loaded trailer's tongue or pin weight.
For mountain routes, follow the vehicle maker's guidance on Tow/Haul mode, gear selection, speed, cooling, and warning messages. Some manuals recommend reducing accessory load or changing air-conditioning settings if temperatures rise, but the correct response is vehicle-specific. Do not rely on generic temperature targets or one-size-fits-all driving instructions.
Keep the cooling-air path in good condition and check for debris during routine maintenance. Follow the vehicle maker's cleaning instructions; delicate heat-exchanger fins can be damaged by aggressive cleaning.

Frequently asked questions about the Davis Dam test

Does every truck have to climb the actual Davis Dam road?

No. SAE has reported that automakers can reproduce the grade profile with a towing dynamometer. The applicable procedure and the manufacturer's testing determine how the vehicle is evaluated.

Is 40 mph the minimum for every vehicle?

No single number should be treated as universal. Published summaries distinguish vehicle categories, and the exact criteria belong to the current SAE procedure.

Does passing the gradeability test mean a trailer is within every limit?

No. The loaded vehicle and trailer still have to stay within all applicable towing, payload, axle, tire, hitch, and trailer limits.

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