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Discussion Starter #1
Curious if you have noticed a, or some, best speeds for your car to get it's best MPG?
I've noticed that on both my 11 and 13 Eco MTs, 66-68mph seems to be the sweet spot. I will typically be at 45+ mpg (sometimes closer to 50). but above or below that speed it will drop linearly.
 

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On my hyper mile to Lordstown I found 55-60 to be the most efficient. 55 was ideal but traffic became a problem. 60 traffic wasn’t too bad and drag not a huge % more.
 

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Best speed for efficiency will be the slowest you can go while remaining in 6th gear.
 

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2015 Chevrolet Cruze LT 1.4L Turbo
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I got 42 mpg average on a 400 mile trip a few weeks ago. My average speed was 54 mph according to the DIC. I drove 65-70 mph most of the way. But tomorrow I'm installing my E85 flex fuel kit so we'll see what the mpg turns into.
 

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18 1.4 auto, absolutely loves 52-56 mph. I can approach 47mpg(actual) over a 50mile stretch of road.
 

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In my 18 1.6 diesel manual I find around 65 seems to be the hot spot. It loves anything between 60 and 70 mph. I tend to let the speed vary to maximize the benefit of momentum.
 

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I noticed @70 MPH seems to be a sweetspot with the 1.4s I had. Only problem the traffic and the hills around where I live so I rarely see it.
 

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50 mph gets me 55 mpg. Flat stretch.

17 1.4

Haven't done it with the car yet. But there's a stretch of 40 miles mostly down. At the bottom of my state. A semi doing 75 mph will average 100 mpg by the time they got to the state line. It's a crap shoot from there.

Turn around and up that same stretch and the number is 1.75
 

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No. LOL. My hatch loves 55mph as I said. Even approaching 65mph I'll still average about 42mpg. That car breaks 70mph and the fuel economy tanks. A 72mph trip is unlikely to get more than 35mpg. Most likely the Redline roof spoiler and hatch shape in general causing the huge drop and the lower sweet spot compared to sedans
 

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Discussion Starter #12 (Edited)
Best speed for efficiency will be the slowest you can go while remaining in 6th gear.
Doesn't seem that way at all for me. I have two work "loops" that I have driven hundreds of thousands of miles. One is interstate, the other highway. Both are extremely similar in elevation change (as indicated on topo maps) at 61mph the absolute best i can achieve is 42mpg. Typically its 39mpg.
At 68mph is where I see 45mpg
I've tested this theory out by driving slower on the interstate and faster on the highway and it holds true.
 

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Doesn't seem that way at all for me. I have two work "loops" that I have driven hundreds of thousands of miles. One is interstate, the other highway. Both are extremely similar in elevation change (as indicated on topo maps) at 61mph the absolute best i can achieve is 42mpg. Typically its 39mpg.
At 68mph is where I see 45mpg
I've tested this theory out by driving slower on the interstate and faster on the highway and it holds true.
Is your engine RPM lower at 61 or 68 MPH? I suspect you're actually in 5th gear at 61 MPH.
 

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You didn't answer my question. What's your engine speed at 61 and what is it at 68?
I’ll also add a question, how is it more fuel efficient when air drag gets exponentially higher as speeds go up. All research and testing shows higher speeds equals more drag thus less fuel mpg
 

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There's a crossover point on all vehicles, at which aerodynamic drag and other frictions require an amount of power greater than the engine can create at its optimum brake specific fuel consumption. It's different for all vehicles. It's very possible for one vehicle to have a maximum efficiency at a higher speed. This is why the HB has a different fuel economy rating than the sedan even though they share drivetrain, and the hatch is nominally lighter.
 

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Discussion Starter #20
You didn't answer my question. What's your engine speed at 61 and what is it at 68?
As close as I can tell via the tach, [email protected], 2050/[email protected]
I absolutely know what you are saying, that it's impossible to get better mpg when the engine is spi nning faster and there is more wind resistance. I'm not at all disputing that should be the case. What I am thinking is similar to what was mentioned by Maven, a point where the engine is creating enough hp/tq that it can overcome the increase in wind resistance and actually be more efficient at that rpm/mph than at a lower one. It seems 68 is right about at that point in my vehicle vs 61. If I bump up to 70mph or above, the mpgs drop.
 
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