SAE Tow Ratings - Tow Ratings Finally Pass the Sniff Test

Don Sherman
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Acceleration Performance Requirements

The tow vehicle must meet these level road performance criteria to merit a particular TWR:

  • Acceleration from zero to 30 mph in 12.0 seconds or less in vehicles with a single rear wheels.
  • Acceleration from zero to 30 mph in 14.0 seconds or less in vehicles with dual rear wheels.
  • Acceleration from zero to 30 mph in 16.0 seconds or less in vehicles with dual rear wheels and a GVWR over 13,000 pounds.
  • Acceleration from zero to 60 mph in 30.0 seconds or less in vehicles with single rear wheels.
  • Acceleration from zero to 60 mph in 35.0 seconds or less in vehicles with dual rear wheels.
  • Acceleration from zero to 60 mph in 40.0 seconds or less in vehicles with dual rear wheels and a GVWR over 13,000 pounds.
  • Forty to 60 mph passing acceleration in 18.0 seconds or less in vehicles with single rear wheels.
  • Forty to 60 mph passing acceleration in 21.0 seconds or less in vehicles with dual rear wheels.
  • Forty to 60 mph passing acceleration in 24.0 seconds or less in vehicles with dual rear wheels and a GVWR over 13,000 pounds.

Grade Launch Requirements

The tow vehicle must be capable of repeatedly moving from rest for a distance of 16 feet on a 12-percent grade in both forward and reverse directions. Five such launches must be accomplished within five minutes in each direction.

Highway Gradeability

To merit a particular TWR, a vehicle must be capable of maintaining a minimum cruising speed while climbing the grade at Davis Dam on state roads 68 and 163 in Arizona and Nevada. This 12-mile-long run originating in Bullhead City, Arizona, involves grades that vary between 3- and 7-percent with an average over 5-percent. During this test, the minimum acceptable ambient temperature is 100-degrees F. and AC systems must be operating on the maximum cold setting with no recirculation and the blower at the highest possible setting.

Single rear wheel vehicles must be able to maintain an average of at least 40 mph on this grade. Dual rear wheel vehicles are required to maintain 35 mph or more here. Dual rear wheel vehicles with a GVWR over 13,000 pounds must maintain at least 30 mph.

To pass these hot-ambient-temperature, steep-grade challenges, there can be no vehicle component failures, no warning lamps, and no diagnostic codes alerting the driver. In addition, the tow vehicle cannot lose any engine coolant. The vehicle under test must be equipped with the lowest numerical axle ratio available from the manufacturer.

Handling Requirements

Standard J2807 specifies that an understeering handling attitude must be maintained up to at least 0.4g cornering without a weight distributing hitch. With a weight distributing hitch (which transfers vertical load from the tow vehicle's rear wheels to its front wheels), an understeering attitude must be maintained up to only 0.3g cornering.

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