Weight-HP ratio?
09-23-2008, 11:16 AM
#3
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Given the 3500lbs weight above, the passenger of 160lbs will use almost 4.6% of the power that is applied _to acceleration_.
Note that there periods of time during acceleration from a stop that tire traction is your limiting factor (on a normal f-body). Your passenger's weight actually helps you gain more traction. Let's assume 75% weight applied to the rear axle during heavy acceleration due to seat position. More traction means more power can be applied to accelerate the car. So when traction is your limiting factor I would say only 1/4 of boston's answer: 4hp. However, traction isn't the limiting factor very long.
Next, when you're at speed you're fighting parts friction and wind resistance, with leftover power going to acceleration. Since a smaller fraction of your power is applied to acceleration, a smaller amount of power is used to accelerate your passenger. For example, at max speed you're not accelerating, and the passenger weight uses zero hp (probably helps lower air resistance actually since your car is lower on the springs).
Without more figures and more math, I'd have to guess 1% of rwhp at launch (or even better if the passenger is in the back seat) for a short time. Then up to 3-4% of rwhp as traction matters less, linearly dropping off to about 1% rwhp lost as you finish the quarter (then down to zero if you eventually hit your top speed).
Note that the extra weight is really going to hurt handling. So leave your passenger out at the road course.
Note that there periods of time during acceleration from a stop that tire traction is your limiting factor (on a normal f-body). Your passenger's weight actually helps you gain more traction. Let's assume 75% weight applied to the rear axle during heavy acceleration due to seat position. More traction means more power can be applied to accelerate the car. So when traction is your limiting factor I would say only 1/4 of boston's answer: 4hp. However, traction isn't the limiting factor very long.
Next, when you're at speed you're fighting parts friction and wind resistance, with leftover power going to acceleration. Since a smaller fraction of your power is applied to acceleration, a smaller amount of power is used to accelerate your passenger. For example, at max speed you're not accelerating, and the passenger weight uses zero hp (probably helps lower air resistance actually since your car is lower on the springs).
Without more figures and more math, I'd have to guess 1% of rwhp at launch (or even better if the passenger is in the back seat) for a short time. Then up to 3-4% of rwhp as traction matters less, linearly dropping off to about 1% rwhp lost as you finish the quarter (then down to zero if you eventually hit your top speed).
Note that the extra weight is really going to hurt handling. So leave your passenger out at the road course.
Last edited by smcnealy; 09-23-2008 at 11:42 AM. Reason: the more I think about it, I want to say 3-4% instead of 2-3%.
09-24-2008, 12:12 PM
#4
I was always told that 100lbs = .1 in a quarter. I know thats not along the lines of your question, but it makes sense if you think that 10hp usually picks you up a tenth. So 160 lbs = .16 seconds off your time, or 16 horse.