SAE J2807-Performance Requirements for Tow-Vehicle Ratings

j2807

The following is a summary of SAE J2807

SAE J2807 is a standardized guideline that defines how Gross Combination Weight Rating (GCWR) and Trailer Weight Rating (TWR) should be determined for passenger vehicles, SUVs, and light-duty trucks. The standard ensures a consistent, objective, and fair comparison of towing capacities among different manufacturers.

1. Purpose and Scope

• Establishes minimum performance criteria for vehicles towing trailers.
• Standardizes test procedures to ensure comparable results.
• Applies to vehicles up to 13,000 lbs GVWR (Gross Vehicle Weight Rating).

2. Test Criteria for Tow-Vehicle Ratings

2.1 Acceleration Requirements

J2807 sets specific time limits for vehicles towing their maximum rated load. Testing is conducted on a level road using the following equations:

Key Equations for Acceleration Testing

• Power-to-Weight Ratio:

• HP = engine horsepower
• GCWR = Gross Combination Weight Rating (tow vehicle + trailer)
• Acceleration Times (Modified SAE J1491 Method):
  • 0-60 mph (0-96.6 km/h)
    • ≤ 30 sec (Single Rear Wheel)
    • ≤ 35 sec (Dual Rear Wheel)
  • 0-30 mph (0-48.3 km/h) Interval:
    • ≤ 12 sec (Single Rear Wheel)
    • ≤ 14 sec (Dual Rear Wheel)
  • 40-60 mph (64.4-96.6 km/h) Interval:
    • ≤ 18 sec (Single Rear Wheel)
    • ≤ 21 sec (Dual Rear Wheel)

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2.2 Gradeability Testing (Hill Climb Performance)

• Vehicles must be capable of launching from a stop on a 12% incline both forward and in reverse.
• The minimum speed must be maintained while towing on the Davis Dam Grade.

Key Equations for Gradeability

• Adjusted Gross Combination Weight for Test Grades

• testgradetestgrade is the percentage of the test incline.
• Power Requirement to Maintain Speed on Grade

• g = acceleration due to gravity (32.2 ft/s² or 9.81 m/s²)
• θ = inclination angle of the grade
• Rolling resistance is determined based on tire and road characteristics.

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2.3 Highway Gradeability (Davis Dam Test)

• Vehicles must maintain a minimum speed of 40 mph (single rear wheel) or 35 mph (dual rear wheel) while climbing the Davis Dam Grade at 100°F ambient temperature, with the air conditioning running.

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2.4 Handling & Stability Requirements

• Vehicles must demonstrate understeer characteristics when towing.
• A weight-distributing hitch should restore front axle load (FALR) adequately to maintain control.

Key Equations for Handling and Understeer

• Front Axle Load Restoration (FALR)

Where:

• WfUT−V = Front axle weight of the uncoupled tow vehicle
• WfCT−V = Front axle weight of the coupled tow vehicle (no weight distribution)
• WfCT−Vwd= Front axle weight of the coupled tow vehicle with weight distribution

• Understeer Requirement:

• δ = Steering angle
• A_y = Lateral acceleration

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2.5 Braking Requirements

• Vehicles towing a fully loaded trailer must stop within the defined distance in normal and emergency braking conditions.
• Trailer brakes are required for any trailer over 3,000 lbs GVWR.

Key Equations for Braking

• Braking Force Calculation:

• μ = coefficient of friction between the tires and the road
• W = weight of the vehicle and trailer
• Stopping Distance Estimation:

• d = stopping distance
• V = initial velocity
• μ = friction coefficient
• g = gravity

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3. Standard Trailer Specifications

To ensure consistency in testing, SAE J2807 defines standard trailers based on weight, size, and configuration.

Key Trailer Characteristics

• Standard Axle Configurations: Single or Tandem
• Maximum Effective Tongue Lengths: Ranges from 83 inches to 420 inches
• Minimum Frontal Area Requirements: Ranges from 12 ft² to 75 ft²

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4. Tow-Vehicle Structural Requirements

• Ensures hitch receivers, frames, and attachment structures meet SAE J684 and SAE J2638 standards.
• Establishes durability and deformation limits for weight-carrying hitches, weight-distributing hitches, fifth-wheel, and gooseneck towing.

Key Equation for Structural Strength

• Angular Deformation Limit for Hitch Attachments: θ_max = 5^∘ , where:
  • θ_max = Maximum permanent deformation angle.

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5. Industry Impact and Adoption

• SAE J2807 ensures accurate, comparable, and realistic towing capacities.
• Major automakers (GM, Ford, Toyota, etc.) have adopted the standard for towing ratings.
• Consumers benefit from safer towing experiences and more transparent vehicle specifications.

Conclusion

SAE J2807 is a critical towing standard that enhances vehicle ratings’ safety, consistency, and transparency. Establishing objective testing criteria for acceleration, braking, handling, and structural integrity allows consumers to make informed decisions when choosing a vehicle for towing.