bradley@godot.UUCP (Bradley C. Kuszmaul) (06/20/84)
It may actually be the case that you got better milage at 62 than 55
because of a number of factors (possibly including that your toyota
is better tuned for 62 than 55) but you just can't get around the
fundamentals of air resistance. At highway speed air resistance
(and other friction: inside the engine, tires etc.) is what eats
fuel, and air resistance goes up like the square of your speed (or
is it the cube... something goes up like the cube. sigh) so 75 mph
is going to be roughly twice as expensive as 55 mph. I have empirically
verified this in the following vehicles
72 volvo station wagon (presumably built for high speeds since
it is pre 55 mph)
72 vw window van. (same comment, except being german where the
autobahns rule more so)
78 honda civic cvcc
66 jeep (not fair since it is badly shaped, but fuel economy
dropped from 14 at 45mph to 10 at 55mph to 5 at 65 mph.
--Brad
--
{decvax!cca,ihnp4!mit-eddie,allegra!ias}!godot!bradley,
"godot!bradley@mit-eddie"@MIT-XX.ARPAscw@cepu.UUCP (06/20/84)
In article <141@godot.UUCP> bradley@godot.UUCP (Bradley C. Kuszmaul) writes: >It may actually be the case that you got better milage at 62 than 55 >because of a number of factors (possibly including that your toyota >is better tuned for 62 than 55) [...] the cube. sigh) so 75 mph >is going to be roughly twice as expensive as 55 mph. I have empirically >verified this in the following vehicles > 72 volvo station wagon (presumably built for high speeds since > it is pre 55 mph) > 72 vw window van. (same comment, except being german where the > autobahns rule more so) > 78 honda civic cvcc > 66 jeep (not fair since it is badly shaped, but fuel economy > dropped from 14 at 45mph to 10 at 55mph to 5 at 65 mph. These cars are not exactly what you'd call slippery (Esp. the VW), in fact they are really rather blocky, in addition the honda suffers from being grossly underengined. My '70 Opel GT (esentially a Kadett in a diffrent suit) got marginally better milage at 70 than running slower (28@70 vs 25@60). The engine/trany/rear-end ratios were such that the engine ran at 3500 RPM (MAX torque) @ 70 MPH. The body was esentially the same as the (69?-82?) Vette (actually it's the other way around Opel had the body style first). -- Stephen C. Woods (VA Wadsworth Med Ctr./UCLA Dept. of Neurology) uucp: { {ihnp4, uiucdcs}!bradley, hao, trwrb, sdcsvax!bmcg}!cepu!scw ARPA: cepu!scw@ucla-cs location: N 34 06'37" W 118 25'43"
rs@hou3c.UUCP (rs) (06/21/84)
It is worthy to note that the transmission is also important in determining what the optimum cruising speed is, for fuel ecomony purposes, as well as the other factors. In particular, manual transmission cars are sometimes equiped stock with innappropriate transmissions for highway cruising. For example, my brothers 1973 Datsan Z would get ~20 mpg at 70 mph and ~16 mpg at 60 mph primarily because of the 3rd and 4th gear ratios and the corresponding engine speed. (as well as the mandatory downshifts to get passing power at 60 mph). My 1968 Camaro had a 3 speed manual transmission that was geared such that the engine was turning about 3500 rpm at 55 mph. A lower ratio rear-end would have brought the rpms down for highway cruising, as well as give me more usable power in the lower gears (instead of just buring rubber when a fast start was attempted). A friend of mine did that with his 1978 Z-28 (350 ci. with a 4 barrel carb). His engine used to turn ~3600 rpm at 60 mph and now turns ~2400 rpm at 60 mph. On a recent long distance trip (to Canada) he got ~20-22 mpg on the highway. Bob Switzer AT&T Bell Labs ...!houxf!hou3c!rs