Which of the following statements is true about the two dynamometer speeds?

• A. They are tested at idle only
• B. They are tested at 50% load at 25 mph and 25% load at 50 mph
• C. They are tested at 60% load at 30 mph and 40% load at 60 mph
• D. They require high altitude correction

Answer: (B)

Two-speed dynamometer testing is designed to capture emissions under realistic driving conditions, not just idle. The two operating points used are 25 mph with 50% engine load and 50 mph with 25% engine load. The higher load at a lower speed simulates city driving and acceleration, where the engine works harder at slower speeds. The lower load at a higher speed represents highway cruising, where the engine runs more efficiently but at a higher road speed. Together, these conditions probe how emissions behave across a useful range of engine operation.

Other options don’t match how the two-point test is defined: testing at idle wouldn’t involve these steady operating points, and the two-speed approach isn’t about applying a fixed altitude correction as part of the speeds themselves. The specific pairs listed in the other statements (such as 60%/40% at 30 mph/60 mph) don’t reflect the standard test points used, and altitude correction is a separate consideration rather than part of the defining two speeds.