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Old 07-15-2009, 07:14 AM   #69 (permalink)
MechEngVT
Mechanical Engineer
 
Join Date: Jun 2008
Location: Richmond, VA
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Quote:
Originally Posted by Christ View Post
(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.
I would agree you're roughly in the ballpark. Those "equations" are ballparkin' it anyway and are based more on empirical trending than mathematical/physics theory. I thought that it was more common to say it takes X% more power than you have to shave Y seconds off your ET, as that would be more accurate even at very high power/low ET ends of the scale, and would therefore be more accurate at the opposite end where most ecomodders would play.

I agree also with your edit. Changes in mass, whether rotational/unsprung or static/sprung, will only make notable differences during changes in speed. That said, there are probably changes that would be very difficult to quantify due to effects of cornering and bumps where lighter unsprung mass (and lighter sprung mass to a lesser degree) would be an improvement. If companies can develop shock absorbers that contribute significant electrical charge energy then there is a non-negligible amount of energy used to move the wheels up and down to cover road surface irregularities. Lighter wheel/tire packages will waste less of this energy, even if it isn't recaptured by a regenerative shock absorber.
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