The performance of an engine installed in ‘‘on-highway’’ vehicles can be tested on a chassis dynamometer.
NOTE: Due to driveline inefficiencies and engine-driven accessories, the rated horsepower will be reduced by ap-
proximately:
• 20 percent for single axle vehicles
• 25 percent for tandem axle vehicles
The net horsepower available is called wheel horsepower (WHP).
NOTE: These percentages are used for engine run-in only and are not to be used as absolute figures.
Caution: Before installing or operating a vehicle on a chassis dynamometer, follow all the vehicle manufac-
turer’s safety precautions.
Caution: Low profile radial tires are more sensitive to heat than bias ply tires. Excessive operating time at full
load can damage tires due to overheating. Check the tire manufacturer’s recommendations for the maximum al-
lowable chassis dynamometer operating time.
The following are general safety precautions to be observed while operating the chassis dynamometer.
• Use tires that have more than 160 kilometers [100 miles] on them. Do not use new tires.
• Do not use recapped tires or tires of different sizes or designs.
• Make sure the tires are inflated to the manufacturer’s specifications.
• Remove all rocks or other material from the tread of all tires that will be rotating on the dynamometer
rollers.
• Make sure there is correct overhead clearance for exhaust stacks, air deflectors, or other attachments
above the cab.
• Carefully position the vehicle on the rollers.
• Attach the ‘‘tie down’’ chains to the rear of the vehicle, and put wheel chocks in front of the front
wheels.
• Adjust the vehicle and dynamometer room exhaust system to make sure all exhaust gases are removed
from the room.
• Refer to the chassis dynamometer and vehicle manufacturer’s recommendations and specifications for
testing procedures.
• Make sure there is proper overhead clearance for exhaust stacks, air deflectors, or other attachments
above the cab.
