1980 breakdown of power consumption WRT MPG

[balthazar]

From Popular Mechanics from 1980, wonder what a given 2014 vehicle would look like broken down the same way.

 

BTW, I do wonder how they came to such exacting figures….

[Drew Dowdell]

Well cars are much more slippery these days, so one would hope there would be a redistribution of the percentage away from that.

However, engines and accessories are much more efficient too, so maybe only the overall fuel burn had changed but the percentages remain the same.

[balthazar]

I would guess that today the percentages for accessories (MUCH more than in '80), transmission (more gears), rolling resistance (wider tires) would be up, and aero drag & friction losses would be less. Acceleration/climbing (cars are MUCH heavier now) probably evens out because engines are more power-dense now and don't have to work as hard, even tho they are moving much more weight.

[KevinW]

Why was the average mileage only 12.9 MPG?  This suggests it was operated near top speed for most of the test; the energy loss breakdown would be much different for a vehicle in normal use.

[Drew Dowdell]

There is a new trick with alternators now though,  They can vary the load they place on the engine depending on the amount of load being used. I ran into it once when I was in a Buick Lacrosse on a trip.  I was using a power inverter to power a laptop, plus we had a number of other chargers and stuff plugged in.  There was a noticeable decline in fuel economy.  But on the way back, none of that was used except a phone plugged into a USB port. Over the same route, fuel economy was much improved.

[balthazar]

^ That addresses interior, extraneous power drain, but onboard accessories create their own relatively elevated consumption drains in modern vehicles.

 

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I believe that "7.7 MPG" is incorrectly labeled. 

 

http://www.automobile-catalog.com/car/1980/35960/renault_20_ts.html

states the Renault 20 TS gets 7.7 L/KM (city). That translates to 30.5 MPG U.S..

Edited November 2, 2014 by balthazar