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Going slower on the freeway and saving gas...

There's still wind and rolling resistence to deal with, both of which increase with speed. There's also the issue of keeping the drivetrain itself moving.
Basically though, fuel consumption is a combination of both engine rpm and throttle position. All other things being equal, the higher the rpm's, the more fuel is consumed.

edit: just tell him to stay in the right lane.
 
uh, it might save a little

if you really want to save gas, drive less, otherwise, just drive whatever the speed limit is/flow of traffic
 
Depends on the gearing in the car. My old Mustang came with 3.08 gears and a 5-speed, which meant that 3000rpm = 100mph in 5th gear. My GrandAm GT hits 3000rpm at about 90.
 
Originally posted by: fyleow
My dad does about 100 miles a day with his car and I was wondering, does sticking to 65 actually save gas? I understand that it keeps the engine revs down but will it make much of a difference? He says that past 3000 RPM the engine starts to burn a lot more gas.

But IMO the only gas burning part about driving fast is in the city where you need to burn a lot getting up to speed during starts and stops. If it's the freeway and you're just slowly accelerating up it shouldn't matter as much right?
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What kind of car does he drive?
 
if he drives slow tell him the stay the hell out of the fast lane. I hate people who go 65 in the fast lane.
 
Depends on the car and gears and engine. My Econobox gets decent gas mileage under 3000RPM but starts sucking it down above that. At 3000RPM I think I'm doing 70MPH. If I stay at 65MPH I've gotten 36+ MPG. At 70MPH I got closer to 33MPG at 75MPG It was 31-32... I didn't get a chance to test much above that.

Anyway, 3000RPM Seemed to be MY sweetspot, fast enough that I'm not going stir crazy and still decent mileage. On a trip < 300Miles I'll generally go a bit faster (as traffic permits) as it takes a full tank to notice any difference anyway.



 
i changed the rear gears,from 3.31 to 3.50 and went to the next size shorter tires in my Camaro,
from 245/60/r15 to 235/60/r15
wow my fuel mileage bites,now
i plan on changing the rear tires,to 2 sizes larger,{255/60/r15} i have one,and need to buy 1 more.

sigh,money is snug..

anyways some cars the optimum speed vs gas mileage is 62,some 66mph, etc. some 58mph
and of course this varies with terrain,wind,snow/rain,and so on to ad naseum, 😉

time costs,so do you want to save 10 minutes or $3.75 on gas?

its a trade off.........
 
Originally posted by: fivespeed5
if he drives slow tell him the stay the hell out of the fast lane. I hate people who go 65 in the fast lane.
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Word.

If I'm on the highway, I will do the max my car can handle no matter what the speed limit is... (this is about 110mph, though most times not enough space to go beyond 90 much)
 
i always think about this, driving slower takes less gas but you have to drive for a longer time so at what speed minimizes how much gas you use?
 
Going slow does not always mean better fuel consumption. You have to figure out at what point the a/f ratio is correct. To low rpms... you run rich. Higher = lean.

There is a sweet spot, you just gotta find it.

And tell your dad something, slow people cause accidents!!!
 
Originally posted by: bolsen
Going slow does not always mean better fuel consumption. You have to figure out at what point the a/f ratio is correct. To low rpms... you run rich. Higher = lean. There is a sweet spot, you just gotta find it. And tell your dad something, slow people cause accidents!!!
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???? that is the most incorrect thing I ever heard. Speed and A/F ratio does not correlate. Assuming you are cruising at a speed you are at partial throttle and running in closed loop. The ECM will be trying to achieve the same target A/F ratio regardless of speed. the way you put it makes it sound like the car delivers teh same amount of fuel regardless of rpm!!

The correct answer is about wind resistance and rolling resitance. drag (due to air) increases w/ the square of speed. not sure about rolling frictional resistance. the car mpg figures I think are taken at about 65 mph..so that is what you should achieve at that rate. for example my car should get 30 mpg highway. i drive around 80 mph so i get around 26mph
 
Many will frown on this, and it is pretty rude, but there is a way you can get 100+ mpg.

Tailgate an 18-wheeler. The way the air flows around the truck when it is moving there is a spot a few feet behind the truck where the air is actually moving forward FASTER than the truck is moving to fill the slight vacuum immediately behind it. When you find this spot you will coast along at highway speeds without actually touching the gas pedal.
 
Originally posted by: eakers
i always think about this, driving slower takes less gas but you have to drive for a longer time so at what speed minimizes how much gas you use?
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Well it is MPG, so if the miles driven remains constant, then the best MPG would use the least gas.

 
Originally posted by: glugglug
Many will frown on this, and it is pretty rude, but there is a way you can get 100+ mpg.

Tailgate an 18-wheeler. The way the air flows around the truck when it is moving there is a spot a few feet behind the truck where the air is actually moving forward FASTER than the truck is moving to fill the slight vacuum immediately behind it. When you find this spot you will coast along at highway speeds without actually touching the gas pedal.
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hrm, what size car though? i can certiantly feel it a lot easier behind a semi, but i still have to use a bit of gas..:-\ then again i'm in a midsize suv
 
my dad is an engineer for UP... i saw a graph for their engines a few years ago that said with throttle at 100% they burnt 45 % more fuel than they did with throttle at 70%.....

i know that's a V - 16 engine with pistons larger than a human head... but it's gotta transfer over at least a little 😀
 
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