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02-16-2009, 08:15 PM   #5 (permalink)
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in 1/2x the time

Quote:
 Originally Posted by winkosmosis Don't you end up using 4x as much fuel at 2x the speed, because one of those 2x is cancelled out by getting to your destination in 1/2x the time?
We have to consider each vehicle on a case-specific basis, along with it's BSFC map under all operating regimes and changes to rolling resistance and any effects of road conditions,grades,temps,wind,etc.-------------------- For the aero portion only,doubling the velocity increases the road load power requirement by a factor of eight.The rolling resistance will not vary the same way.So you've got to calculate the total road load for any given speed.------------------- Using my truck for an example,at say 40 MPH you'd see low 40s mpg,and then pushing it to a steady 80 mph she falls off to around 30mpg.----------------- At the low speed the truck is mainly battling rolling resistance with only marginal air drag.At 80 mph,about 80% of available engine power is being absorbed by aero drag.--------------------- Every individual has to way out the implications of the higher velocity.