Fuel economy/gas mileage, highway driving. N00b question

[TheLandYacht]

OK. Noob owner of a 2018 stock Mirage ES (Automatic transmission) here. Just bought it used with...get this, only 10k miles on the clock. Why the original owner put so few miles on this baby I don't know, but it's pristine. Before you ask, I bought it off CarMax, who are notorious for buying it back within 30 days...and the first thing I did was run about 500 miles on it, then take it to a mechanic & have him do a stem-to-stern, top-to-bottom inspection. It's clean as a whistle. AND...the original owner never registered with Mitsu as far as I can tell, so I may be able to claim the 100k powertrain warranty.

On to my question, which will probably start an argument among the hard-core gas-mileage tweakers.

Given a relatively flat & straight travel path...what's the "sweet spot" for speed & tach, to set the cruise for highway travel? I have to travel 40 miles each way to commute to & from work each night for work.

Thoughts?

[inuvik]

OK. Noob owner of a 2018 stock Mirage ES (Automatic transmission) here. Just bought it used with...get this, only 10k miles on the clock. Why the original owner put so few miles on this baby I don't know, but it's pristine. Before you ask, I bought it off CarMax, who are notorious for buying it back within 30 days...and the first thing I did was run about 500 miles on it, then take it to a mechanic & have him do a stem-to-stern, top-to-bottom inspection. It's clean as a whistle. AND...the original owner never registered with Mitsu as far as I can tell, so I may be able to claim the 100k powertrain warranty.

On to my question, which will probably start an argument among the hard-core gas-mileage tweakers.

Given a relatively flat & straight travel path...what's the "sweet spot" for speed & tach, to set the cruise for highway travel? I have to travel 40 miles each way to commute to & from work each night for work.

Thoughts?

Keeping your speed 65 mph or under and use cruise control every chance you get.

[MrMPG]

Can confirm 60-65mph being the sweet spot on my 2022 CVT Mirage G4, Regularly average 50-55mpg as i do a 66 mile daily highway round trip. AC will knock it down the the high 40s usually.

[Space Wolf]

What do you mean with 'sweet spot' here? Normally a sweet spot is the place where two conflicting requirements have a combined peak (or off-peak, depending on the curve/units).
I suppose you are trading economy for travel time here. In that case the sweet spot is personal, as you can't weigh travel time for someone else. If it's just about getting the best economy then I believe the peak is somewhere between 30 and 50 km/h, 20 and 35 miles an hour. When you go faster, the drag lowers the economy, when you go slower the overhead of the engine becomes too big.
35 miles on a highway is a bit impractical, and maybe illegal, but basically you should drive as slow as you want (and are allowed) to go to get the highest economy.

[inuvik]

Can confirm 60-65mph being the sweet spot on my 2022 CVT Mirage G4, Regularly average 50-55mpg as i do a 66 mile daily highway round trip. AC will knock it down the the high 40s usually.

55-60mph will give you better mpg's but you might get run over in most of the USA unless you are driving in very rural areas with no traffic or the Southern Oregon Coast where I find many people driving well under the 55 mph speed limit .

[TheLandYacht]

What do you mean with 'sweet spot' here?

I guess by "sweet spot" I was meaning the point where I would get the best result. The "sweetest" spot, so to speak. I didn't know there was an actual technical term that meant something different.

On to the next layer(s) of the puzzle. Looks like my route isn't as flat as I'd assumed because the gauged mpg on my nightly commute is radically different one way than it is the other. I'm assuming because of a consistent uphill grade (I do live in the "Hill Country").

For reference:

36mpg gauge one way
42mpg gauge the other way

Which doesn't match at all to what I calculated today with 3 fill-ups (I don't wait 'til it's anywhere near empty, can't risk it out in the sticks where gas stations are rare so I gas up around 1/4 tank)
626.4 miles travelled
17.932 gallons used.
34.932 mpg average?

I think I need to moderate my foot...a LOT. And that's with me using the cruise-control almost exclusively, and almost all highway driving.

Still better than my wife's big truck that gets 13mpg. We don't use that thing unless we absolutely have to.

[mohammad]

The answer to your question maybe found in the diagram shown here: https://mirageforum.com/forum/showth...age-1-2L-5-spd Basically slower is better. If your reading the MPG off the car MID screen there's a consensus on this forum that it displays a slightly optimistic reading, something like 5%. Also note that the first few KM of driving will always be worse as the engine needs to warm up and it needs to waste gas to heat up the catalytic converter, read more here: https://mirageforum.com/forum/showth...ment-when-cold

[TheLandYacht]

55-60mph will give you better mpg's but you might get run over in most of the USA

....and will ABSOLUTELY get you run the hell over in Texas, where we drive like a bat outta hell, anyway. The speed limit is considered a suggestion here. And the speed limit on the road(s) I travel to/from is 70mph for 75% of my commute, on a 2-lane road. 60mph on the rest.

[AtomicPunk]

I guess by "sweet spot" I was meaning the point where I would get the best result. The "sweetest" spot, so to speak. I didn't know there was an actual technical term that meant something different.
.

It's not. You used it correctly.

[7milesout]

....and will ABSOLUTELY get you run the hell over in Texas, where we drive like a bat outta hell, anyway. The speed limit is considered a suggestion here. And the speed limit on the road(s) I travel to/from is 70mph for 75% of my commute, on a 2-lane road. 60mph on the rest.

TLY - I don't know the CVT. But in the 5 speed, it would probably be the speed at which the engine runs at maybe about 2,000 rpm in 5th gear (~40 mph). The problem is, that's too slow for interstate cruising. This is all a math problem. The wind drag being an exponential curve. But it does seem like above 65 mph, the mpg penalties start escalating quickly.

Therefore, the "interstate sweet spot" is probably going to have to be 65 mph, to minimize trouble from those behind ... who're driving their QX80's at 86 mph while making a ticktock recording.

Texas has the highest speed stretch of road in all the U.S. I forget the name / number. Seems like it is just north of Austin.

Atlanta's I-285 loop has got to be the most unregulated interstate in the whole U.S. I bet, we could arrange an all-Mirage race. Say just 10 Mirage's get together and cruise along on I-285 2 x 2 (like a nascar start), and then all 10 Mirages go at the same time and race a loop around I-285.

I would wager a) we never see the first cop, and b) I wouldn't wager this one, but there's a decent chance people might not know that we're racing because 100 mph is barely faster than quite a large percentage of drivers on I-285 anyway. And with traffic, the Mirages are not going to be hitting 100 mph much. And, c) I think such an event would be fun (but way too dangerous).