[Info-vax] Off-topic follow-up, now with actual data - mileage vs. speed

[Phillip Helbig---undress to reply]

In article <bb1a275b-6086-4a71-b60f-faa48bd50134 at googlegroups.com>,
alanfeldman48 at gmail.com writes: 

> A while back, I think twice even, discussion of gas mileage came up for some 
> reason. Many here claimed higher speeds get better mileage. 

Up to a point, Lord Copper.  Driving at 50 mph in 4th gear will get me 
better mileage than driving 20 mph in first gear.

> I claimed that 
> going at low RPMs in the highest gear gets the best mileage 

Right.

> (maybe about 50 
> mph). 

Depends on the car, but this is in the right ballpark.

> I made similar runs on previous dates, but only kind of averaged the readings 
> in my head. I *always* clearly got better mileage at lower speeds. 

Of course.  The primary consumer of power is wind resistance, and that 
goes with the square of the speed.  However, this can be offset by the 
fact that the engine is running to fast at lower speeds IN LOWER GEARS.

> It's clear: 55 mph gets much better mileage than 75 mph.

Yes, of course.  

> Hey, I'd rather it be different, but it isn't. With highway driving there 
> is a 
> trade off between speed and mileage. Time saved vs. gas saved. You have to 
> drive with the laws of physics you have, not the laws you might want.

Right.  Driving at 60 mph, I get about 60 mpg.  Driving at 100 mph, I 
get about 40 mpg.  So, driving faster costs more, but saves time.  If 
this is time which would otherwise be earning money, then you have to 
have a low wage indeed not to justify driving as fast as possible IN AN 
INEXPENSIVE CAR.  When one pays more than the minimum for a reasonable 
car ($15k, say), then one enters a realm of diminishing returns.  People 
who earn enough that it is worth it to them to be able to travel 150 mph 
earn enough that they don't have to worry about this in the first place.