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Originally Posted by ERTW
my thinking is: you run a car at a certain speed, a certain rpm, and load (which determines bsfc). reducing aero load simply gives the same load at a higher speed - with the same rpm and load on the engine (with appropriate gearing). so your 32 mpg at 100 mph is not the issue.
mechanical friction increases with the square of the speed. Reduced wind drag means mechanical friction is the significant loss to accordingly higher speeds. Wind drag increases with the cube of the speed, so there is a definite benefit to higher speed/lower drag.
I'm interested in seeing those SAE standards. I was under the impression that the fuel economy curve is an inverted bathtub...so at best l'd expect the plateau to extend higher...not climb drastically as you state.
Now you'll have to police drivers without appropriate licenses - and more importantly, the necessary skill to handle the car. how many new licenses will it take before the state drops millions of dollars to build a special lane? How do you police drivers from out of state? Driver training would have to be raised in the entire north america (way too low a standard). Germany's standards seem appropriate - 18+, $3000, graduated licensing, yearly car inspections, regular recert, know how to change your oil, etc).
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The SAE papers I have give the mechanical power train losses as constants:
*A transmission would be 95% efficient (up to 6-speeds)
*A differential/rear axle would be 96%
*A propeller shaft,98%.
*An entire pickup truck power train is 92% efficient as measured between flywheel and road interface.
*I allowed 94% for the Honda Accord's transverse layout with either lockup torque converter or manual trans.
Since the 'Road Load' of the 100 mph car is identical to the 75 mph car,no efficiency variable exists.
A Gear Vendor (Doug Nash Racing Transmissions) unit uses a 1:1 output ratio for top gear in its 'overdrive' transmission.All gear-matching is done with the ring and pinion with no losses in the transmission itself.(something a 100 mph car might incorporate).
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As far as the fuel economy goes,I'm using Honda's BSFC as a constant (which can be achieved with the gear-matching) and a fixed Road Load horsepower.
I've compensated for the higher rolling-resistance loss (read directly off Honda's power curve).
The difference in aero load which must make up the difference is solved for using the standard aerodynamic power equation with standard SAE barometric conditions,and yields the Cd 0.125 necessary to make the fit.
The power absorption coefficient is presumed constant with Z-rated rubber,held below standing wave velocity.
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As for any fuel economy testing,you'd follow SAE on-road protocols for temps,wind,precipitation,road conditions,grade,curvature,and banking.
This has nothing to do with EPA certification lab testing.This is real world on road, steady-state highway cruise speed mpg.