What is the ideal speed for best mpg?

[bugaboo90]

So, I assume mpg is a parabola with a knee bend somewhere.. So, does anyone know what the ideal speed is for highway and city to optimize mpg? I think I understand the if I keep my speed steady (ie use cruise) it will maintain the best mpg versus speeding up and slowing down.
But I assume based on gearing, there is a speed that I should maintain to optimize my mpg. Anyone know?

Or is it an invalid question?

 

[AV8R]

Believe it or not I have found if i accelerate to 130kph I get the best fuel economy. If I cruise below 100 I use more fuel. This is not in any particular car. I think you have to consider minimum power to overcome drag so windows open make a difference.

 

[mldavis2]

It used to be around 45-50mph. Don't know today with 8 and 10-speed transmissions.

 

[bugaboo90]

Ya, I think I observed the same thing. 80 mph seems to be the highway sweetspot.

Believe it or not I have found if i accelerate to 130kph I get the best fuel economy. If I cruise below 100 I use more fuel. This is not in any particular car. I think you have to consider minimum power to overcome drag so windows open make a difference.

 

[GuyManDude]

Parked for me otherwise I’m always testing the throttle.

 

[iclicku]

I seem to get the best at 65-70

 

[STNGRNV]

I always heard it after 60mph fuel economy started to suffer exponentially. But that was years ago and who knows if it was ever true in the first place.

 

[mldavis2]

The Stinger is quite a bit more aerodynamic than most cars so speeds might be a bit higher before drag becomes a major factor.

 

[bugaboo90]

I wonder how gearing fits into mpg along with aerodynamics.

The Stinger is quite a bit more aerodynamic than most cars so speeds might be a bit higher before drag becomes a major factor.

 

[Chris]

I would assume the most fuel efficient speed is the slowest you can go in the top gear without the engine bogging.

 

[Berzerker]

While the 8-speed certainly helps, at least on what the fuel economy gauge is telling me, it takes a lot less gas to hold 55mph than it does to hold 80mph.

I would venture to guess that because the car is long and heavy is why we're not as good with fuel.

 

[Merkur720]

It seems strange, but I find my highway fuel mpg improving when in sport mode. Almost like it does better running in 7th gear hovering around 2k rpm. The average MPG gauge seems to swing less during inclines and declines than it would in 8th gear in comfort/eco.

Eco seems to be best for slower city traffic though.

 

[bugaboo90]

That's interesting. Ill have to try it this weekend. Thx

It seems strange, but I find my highway fuel mpg improving when in sport mode. Almost like it does better running in 7th gear hovering around 2k rpm. The average MPG gauge seems to swing less during inclines and declines than it would in 8th gear in comfort/eco.

Eco seems to be best for slower city traffic though.

 

[mldavis2]

I am fascinated by this powertrain. Most high performance engines have a fairly balanced torque/horsepower comparison. For example my GTO LS2 is 400/400. The Lexus RC500 is 398/471 and the Stinger is 376/365 with virtually identical performance specs to the RC500 but lower mileage. The Stinger is very "torquey" no doubt related to the use of turbocharging, but it also suggests that the final drive gearing of the Stinger is a bit lower than the RC500. So the Stinger somewhat over-performs in acceleration but under-performs for economy. Another variable is the "smart" transmission that seems to be very adept at keeping the engine in mid-torque range and away from pushing it off the top end where the torque begins to drop away. And we also have information that the computer "learns" a driver's "style" and adjusts accordingly over time. And you have five drive modes and nearly endless combinations of modes, driver styles, fuel octane and a few other incidental things like wind direction and terrain. It could be that the engine "lugs" a bit in 8th gear at moderate highway speeds. I'll have to see if I can find the final drive ratios of that gearbox.

Another thing I have found over the years is that I can do a slightly better job on fuel mileage on my GTO and G8 if I do NOT use the cruise control. My theory is that because I can see the upcoming road conditions (hills, etc.) I can anticipate throttle position rather than waiting for the engine to load/unload and then reacting after the fact. Yes, modern computers are faster than they were 10-13 years ago and this might be a non-issue now, but I'm skeptical that I can't do better than the cruise control by concentrating and anticipating a run-up or coast-down.

And I think Kia has been extremely conservative with their stats as indicated by the relative performance of the engine compared to other similarly powered cars, so perhaps the 25mpg is also as conservative. I'll bet I can do better on a long trip.

 

[AV8R]

I wonder how gearing fits into mpg along with aerodynamics.

Well, the more drag the more power you need to overcome just like carrying more weight. Even though I’m talking aerodynamics you still have to overcome friction from the road and parasite drag as you go faster. Parasite drag is made up from form drag and interference drag ie the shape of the car and how streamlined it is plus the way the wind flows around and over the car. Once you are at a constant velocity you back off a bit on the accelerator and your momentum helps a little. The issue is finding a happy medium that gives you the sweet spot. Of course the gearing applies too. Thus Endeth the science lesson

 

[STNGRNV]

Another thing I have found over the years is that I can do a slightly better job on fuel mileage on my GTO and G8 if I do NOT use the cruise control. My theory is that because I can see the upcoming road conditions (hills, etc.) I can anticipate throttle position rather than waiting for the engine to load/unload and then reacting after the fact. Yes, modern computers are faster than they were 10-13 years ago and this might be a non-issue now, but I'm skeptical that I can't do better than the cruise control by concentrating and anticipating a run-up or coast-down.

Yeah, cruise control helps on flats, but going uphill and downhill it uses more gas than it needs to. People who "hypermile" recommend not using it.

 

[Never thought]

Oddly enough, it seems like I get better MPG in Sport mode too

 

[bugaboo90]

I just tried this for a couple of hundred miles. I'm not sure if I got better mpg or not in sport mode but I absolutely didn't get any worse mpg and the drive was more pleasant since I had power when I needed it more readily.

Oddly enough, it seems like I get better MPG in Sport mode too

 

[Chris]

I just tried this for a couple of hundred miles. I'm not sure if I got better mpg or not in sport mode but I absolutely didn't get any worse mpg and the drive was more pleasant since I had power when I needed it more readily.

If you are driving down the freeway at a certain rpm in a certain gear, what mode you are in will have absolutely no bearing on the mpg. All it is doing is changing how responsive the gas pedal is and the shift points.

 

[mldavis2]

If you are driving down the freeway at a certain rpm in a certain gear, what mode you are in will have absolutely no bearing on the mpg. All it is doing is changing how responsive the gas pedal is and the shift points.

Doesn't Sport mode keep the car out of 8th gear? That has been reported by someone.