Quote:
Originally Posted by alohaspirit
So 8 lbs off your rim weight = 56 lbs of equivalent basic weight
-.05 faster 1/4 mile time
Dont you wish there was a formula for mpg too
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There is.. I can't find it.
Basically, figure out (for the original weight) how much more HP you'd have to add to shave .1 off your 1/4 mile time, which would give you the HP/Weight equivalent (gaining X horsepower = losing N weight)
You can then compare the weight loss to the horsepower necessity, and since you know that 1 HP = about 750w, you can compare the 750w figure to the actual kW figure of the car that you're theorizing about.
i.e. = Lets assume his car in OEM form weighs 2000 lb, and has 100 HP (75kW)
We'll also assume (incorrectly, but for the sake of example) that he can either drop his weight 100 lbs to lose .1, or gain 10 HP to lose .1
This means that (10HP = -100LBS), or for every 10 HP you add, you will get the same effect as losing 100lbs, and vice versa.
So, based on the above, 10HP = 7.5kW, where the car had 75kW.
We can then assume that losing 100lbs makes for a reduction in necessary HP by about 10%, for this exercise. (Keep in mind, these figures aren't correct, but for the sake of display, they'll have to do.)
So if the car required 35 HP to accelerate from 0-60, it would now only require approx 31.5HP, or 3.5 HP less.
(I actually wonder how far off the numbers are... it doesn't seem outrageous to think that you could use 10% less HP by removing 100 lbs...)
Anyone care to chime in?
EDIT: I think that formula only applies for when you're accelerating though... I don't think it makes that much of a difference when you're just cruising.