6.25 Pounds Drag @ 60 mph = 1 Road-Horsepower
By definition,
1 HP = 33,000 foot-pounds work/minute
One mile = 5,280 feet
1 hour = 60 minutes
60 mph = 1 mile/minute
So divide 33,000 foot-pounds by 5,280 feet to get
6.25 mile-pounds/minute = 1 horsepower
In other words, if a side view mirror is resisted by exactly 6.25 pounds of wind resistance at 60 mph, it is consuming a steady 1 horsepower. Big truck mirrors consume considerably more than 1 horsepower at 60 mph.
Would you like to test how much horsepower specific attached devices like mirrors and exterior spotlights consume at various road speeds? Here's a test procedure that can give sufficiently accurate comparison results to guide decisions.
Attach a common drawer slide to a vehicle's free-air-flowing attachment surface. Lumberyards sell low-priced, sufficiently-strong drawer slides which have low friction. Their end facing the air flow will add little wind drag. If you'd like, you can even zero your spring scale at 60 mph with no test device attached. Your test slide may be attached and detached with removable Velcro adhesive strips. Attach objects you'd like to wind-drag test to the slide. Attach a thin cable or strong fishing line to the slide, pulling it forward about half way between its front and rear stops. Attach a spring scale positioned so you can read it from inside your vehicle while driving. We don't want the scale to chip paint, so tape on some bubble wrap to create a soft bumper. Secure your spring scale's front to a forward attachment point on your vehicle with more cable or strong fishing line.
Wind drag will push your test objects rearward. Your spring scale & cables will resist that rearward push with tension. You will read that tension from inside your vehicle by reading your spring scale. By testing at 60 mph, we can divide observed tension pounds by 6.25 pounds to reveal road horsepower consumed at 60 mph.
Wind resistance pounds increase by speed squared. Horsepower required balance against speed-squared wind resistance increases by speed cubed. Start with 60 mph horsepower values, then adjust for speed accordingly.
If you run some of these tests, please post your results telling exactly what device you tested, wind resistance you observed at 60 mph and your calculated horsepower estimate.
If you're not sure where actual 60 mph appears on your speedometer, adjust your cruise control until Interstate mile markers come up at exactly 60 second intervals. Survey teams set those mile markers pretty accurately.
John
By definition,
1 HP = 33,000 foot-pounds work/minute
One mile = 5,280 feet
1 hour = 60 minutes
60 mph = 1 mile/minute
So divide 33,000 foot-pounds by 5,280 feet to get
6.25 mile-pounds/minute = 1 horsepower
In other words, if a side view mirror is resisted by exactly 6.25 pounds of wind resistance at 60 mph, it is consuming a steady 1 horsepower. Big truck mirrors consume considerably more than 1 horsepower at 60 mph.
Would you like to test how much horsepower specific attached devices like mirrors and exterior spotlights consume at various road speeds? Here's a test procedure that can give sufficiently accurate comparison results to guide decisions.
Attach a common drawer slide to a vehicle's free-air-flowing attachment surface. Lumberyards sell low-priced, sufficiently-strong drawer slides which have low friction. Their end facing the air flow will add little wind drag. If you'd like, you can even zero your spring scale at 60 mph with no test device attached. Your test slide may be attached and detached with removable Velcro adhesive strips. Attach objects you'd like to wind-drag test to the slide. Attach a thin cable or strong fishing line to the slide, pulling it forward about half way between its front and rear stops. Attach a spring scale positioned so you can read it from inside your vehicle while driving. We don't want the scale to chip paint, so tape on some bubble wrap to create a soft bumper. Secure your spring scale's front to a forward attachment point on your vehicle with more cable or strong fishing line.
Wind drag will push your test objects rearward. Your spring scale & cables will resist that rearward push with tension. You will read that tension from inside your vehicle by reading your spring scale. By testing at 60 mph, we can divide observed tension pounds by 6.25 pounds to reveal road horsepower consumed at 60 mph.
Wind resistance pounds increase by speed squared. Horsepower required balance against speed-squared wind resistance increases by speed cubed. Start with 60 mph horsepower values, then adjust for speed accordingly.
If you run some of these tests, please post your results telling exactly what device you tested, wind resistance you observed at 60 mph and your calculated horsepower estimate.
If you're not sure where actual 60 mph appears on your speedometer, adjust your cruise control until Interstate mile markers come up at exactly 60 second intervals. Survey teams set those mile markers pretty accurately.
John
