Best speed for fuel economy?

[NeoPTLD]

What is the best speed for an 85mile, 90% freeway driving? The limits on the freeway are mostly 65 and some 55 area.

I have tried 75-80 on 65, 65 on 55; 70 on 65, 65 on 55 and today I tried 65 all the way through.

Speed doesn't seem to make a whole lot in mean travel time and I'm looking for a way to get the best mileage.

What speed, driving pattern will give me the best mileage? I already avoid unnecessary acceleration and deceleration by using cruise control.

 

[Cooljt1]

the lowest rpm while cruising will normally give you the best gas mileage. also, not using ac or heater will also increase gas mileage

 

[Gravity]

I cruise at 80 mph and 2850 rpm. I get 26.4 overall.

BMW, 328ia, slightly modified.

 

[Eli]

Originally posted by: Cooljt1
the lowest rpm while cruising will normally give you the best gas mileage. also, not using ac or heater will also increase gas mileage

Running the heater doesen't effect your gas milage. It's "free" as far as energy goes, because it would just be wasted anyway.

The answer is probably largely going to depend on the engine, transmission gearing, and the drag of the car. Lower RPMs aren't *always* better, although it's not like you're going to be idling along at 1000RPM down the highway.

If you look at the fuel usage chart for an engine it looks kinda like a C turned on its back. Fuel usage starts out high, and then as the RPMs climb, it actually decreases as engine efficiency rises... And then slightly past a fast idle, it shoots skyward.. say 2500 - 3000RPM.

 

[hans007]

i thought that if you can get your car into the highest gear, and keep the rpms stable that was the optimum.

 

[MAME]

no less than 2k rpms (that would be near impossible anyway on a freeway) and no more than 3k

That will put you around 65mph with a 5 speed manual

 

[Eli]

Originally posted by: hans007
i thought that if you can get your car into the highest gear, and keep the rpms stable that was the optimum.

It is, in general.

But he's asking what the best speed for gas milage is, not the best technique. And the answer is that it totally depends on the car.

IE: 70MPH in one car might give the best gas milage, while anything above 65 in another it falls through the floor..

 

[NeoPTLD]

I have an automatic with OD there's not a whole lot I can do about RPM independent of speed.

 

[Tipe2]

For any gasoline burning engine driven car, 40 to 45 M.P.H., this is largely due to aerodynamics.

Car & Driver got their best mileage traveling at exactly 42 M.P.H. in a Honda CRX while drafting a Ford van some time ago.
As speed increases, the wind resistance and the horsepower to drive the vehicle exponentially increases, don't let anyone tell you otherwise.

If wind resistance played no part in this equation, then your best fuel mileage would peak at the engines torque peak in most instances, this rule does not apply to race engines.

 

[NeoPTLD]

Originally posted by: Tipe2
For any gasoline burning engine driven car, 40 to 45 M.P.H., this is largely due to aerodynamics.

Car & Driver got their best mileage traveling at exactly 42 M.P.H. in a Honda CRX while drafting a Ford van some time ago.
As speed increases, the wind resistance and the horsepower to drive the vehicle exponentially increases, don't let anyone tell you otherwise.

If the engine and transmission efficiency were cosntants, then you can say that efficinecy is -v^2

 

[Tipe2]

I edited my statement at the same time you posted your response

Sorry, I have yet to drink my morning coffee.

Edited once again for my extremely poor spelling

 

[StageLeft]

I've heard that it's around 50 mph.

 

[DurocShark]

My Volvo gives its best mileage/time at around 70mph. The Fiero gets best mileage at around 80. My S10 got its best mileage at 80 as well. My old 1971 Ford LTD got its best mileage at 55.

It definitely depends on the car, though newer cars seem to be able to handle higher speeds more efficiently than older cars.

Of course, the BEST over speed is going to be around 40... whatever speed your car moves at while in the highest gear and rpm's are at a fast idle. heh

 

[Abzstrak]

well, logically it will be below 60mph since aerodynamic resistance is considered negligible below this speed..., I would guess about 75% of that speed, or 45 would be about right for most cars. it REALLY depends on you vehicle though, but it should be below 60

 

[Kelemvor]

Once you go over about 55 or so your MPG goes down. Basically you get the absolute best at the lowest speed you can go in your Top Gear. Most cars hit the top gear right around 50 - 55 MPG so anything over that you are just using more RPMs but not shifting at all so it's using more gas than you gain in speed....

I don't know why the hell no car places have made a gear you shift into right at about 60 to give cars much better fuel efficiency....

 

[rh71]

Originally posted by: Skoorb
I've heard that it's around 50 mph.

I heard 45mph from our drivers ed teacher about 10 years ago (holy $#!t it's been that long). *shrug*

 

[Triumph]

Well obviously the answer is 55 mph.

 

[Viperoni]

The Answer is: It depends on your engine, transmission and car drag.
Your engine reaches peak efficiency at a certain RPM, and depending on your transmissions gear and your cars drag at different speed, the best combination of speed (drag) and engine RPM (efficiency) will give you the best mileage.

 

[CraigRT]

good mileage for me is somewhere around 65-70mph.. my car revs high due to the transmission, but it's the best i can do

 

[NeoPTLD]

looks like its simply more trying and recording...

 

[Analog]

Fuel consumption is directly tied accelerator (throttle) position. I.e., the less you press the gas, the less you use. Put it in the highest gear and go 55. Nobody can say that you will use less gas in the same gear at a higher speedometer speed than this. If they do, then it means they are pulling back the throttle (using less gas) and going faster. I'd like to see that.

Efficiency, however, is a different matter. If someone says that an engine gets higher efficiency at a higher RPM (more throttle), that is perfectly fine, but you are still using more gas than at a lower RPM, albiet with greater efficiency.

 

[conjur]

Originally posted by: NeoPTLD
What is the best speed for an 85mile, 90% freeway driving? The limits on the freeway are mostly 65 and some 55 area.

I have tried 75-80 on 65, 65 on 55; 70 on 65, 65 on 55 and today I tried 65 all the way through.

Speed doesn't seem to make a whole lot in mean travel time and I'm looking for a way to get the best mileage.

What speed, driving pattern will give me the best mileage? I already avoid unnecessary acceleration and deceleration by using cruise control.

Well, yeah, you're only going 85 miles. At an avg. of 85mph you'd be there, obviously, in one hour but that's going to be impossible. At a 70mph avg., it will take you 1.21 hours. At a 60mph avg., it will take you 1.42hours - a whole 12 min. slower...wow.

So, in your case, it would be advantageous to find the best speed for fuel mileage without getting run over!

 

[Pepsi90919]

Running the heater doesen't effect your gas milage. It's "free" as far as energy goes, because it would just be wasted anyway.

you don't just get 'free' energy.

 

[XZeroII]

In my old '87 GrandAm, I had a 5 speed manual and it would run at about 1950RPM's at 65MPH. I would get about 38-40mpg. Once I hit 70MPH, it would drop like mad. At 75, I would get about 30mpg.

Man, if that thing didn't rust apart, I would have put a new clutch in there and ran it another 175,000 miles

 

[RU482]

Originally posted by: MAME
no less than 2k rpms (that would be near impossible anyway on a freeway) and no more than 3k

That will put you around 65mph with a 5 speed manual

Bah, I had a Bonneville that would run 75MPH at 1900RPM
in fact, my van (same engine, similar tranny) will do the same