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Old 05-20-2019, 09:00 AM   #11 (permalink)
prr
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It has been windy the last several days. I couldn't get a historical weather report for the day & area we traveled through, but the nearest I could get a report for also recorded winds above 10 MPH, so that also might have played a factor. These aren't exactly hurricane winds, but they have been continuous throughout the day, and are more than normal.

Quote:
Originally Posted by JRMichler View Post
Some other factors:
Wind. A 20 MPH headwind will decrease my gas mileage by about 3 MPG, with a similar increase if it is a tailwind. Crosswinds hurt mileage similar to headwinds.


Last edited by prr; 05-20-2019 at 09:11 AM..
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Old 05-20-2019, 10:13 AM   #12 (permalink)
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You can never make up your uphill losses by coasting downhill. It certainly helps, but regardless you always have internal fricton, tire friction, and air resistance both ways at a minimum: that is likely where most of your losses came in.

For what it's worth my daily commute I only (yes only) get 40 mpg out of my Geo Metro, but I have 3 very deep, very steep valleys that I have to go through. If I go the other direction to the city we do most of our shopping in I would guess I could easily pull 50 mpg as it's all flat as a board except for one spot it goes under a railroad.
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Old 05-20-2019, 10:16 AM   #13 (permalink)
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Interesting, I would have thought the ability to coast downhill would more than make up for an uphill drive. Interesting point there.

So I guess it was a combination of wind & elevation.

Quote:
Originally Posted by Shaneajanderson View Post
You can never make up your uphill losses by coasting downhill. It certainly helps, but regardless you always have internal fricton, tire friction, and air resistance both ways at a minimum: that is likely where most of your losses came in.

For what it's worth my daily commute I only (yes only) get 40 mpg out of my Geo Metro, but I have 3 very deep, very steep valleys that I have to go through. If I go the other direction to the city we do most of our shopping in I would guess I could easily pull 50 mpg as it's all flat as a board except for one spot it goes under a railroad.
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Old 05-20-2019, 01:01 PM   #14 (permalink)
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That's one of those things that people "know" intuitively: that coasting downhill makes up for expending energy to get up the hill in the first place. In a simplified, idealized world where cars have no aerodynamic drag, no rolling resistance, and no drivetrain inertia or friction, that would be true. But the world is a lot more complex than we imagine most of the time.

I'm working through White's Fluid Mechanics this summer, and the first chapter starts with a discussion of one deceptively simple question: What is the difference between a solid and a fluid? The author points out that most laypeople, even though they "know" what makes the two states different, can't actually define it.
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Old 05-20-2019, 01:37 PM   #15 (permalink)
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My 2015 Rogues best 4 tanks were in CO continuously going up or down and not driving for FE, 8 MPG better than the average. It downshifts (CVT increases engine rpm) when going down hill to increase engine braking. It minimizes the need for brakes a lot.
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Old 05-20-2019, 01:42 PM   #16 (permalink)
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Quote:
Originally Posted by Vman455 View Post
That's one of those things that people "know" intuitively: that coasting downhill makes up for expending energy to get up the hill in the first place. In a simplified, idealized world where cars have no aerodynamic drag, no rolling resistance, and no drivetrain inertia or friction, that would be true. But the world is a lot more complex than we imagine most of the time.

I'm working through White's Fluid Mechanics this summer, and the first chapter starts with a discussion of one deceptively simple question: What is the difference between a solid and a fluid? The author points out that most laypeople, even though they "know" what makes the two states different, can't actually define it.
Fluids flow and conform to a container, solids (mostly) maintain their shape, barring sufficient outside forces. Why is that difficult?
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Old 05-22-2019, 04:55 AM   #17 (permalink)
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To understand FE in a particular vehicle is to have loaded it to stated maximum. A solo driver is abnormal when it’s built for 4-6 people plus gear. Doesn’t matter that’s the way it’s used.

Takes 13-weeks to establish new habits. With cars I’ve always found that 10k miles cements the deal.

In turn, then lightening the load is bettered by the right foots understanding.

MPG claims in otherwise empty cars are a stunt. No value.

Use the vehicle per design, THEN establish what’s best.

My pickup is ALWAYS 1,200-lbs over TARE weight. Add in truck work gear presently with me on the road, and hitch the travel trailer, it goes just OVER vehicle GVWR (but not axle or tire limits). THAT is it’s defined purpose. (As well as my job to get the towing “penalty” as far below 40% as is possible).

For the most part, MPG is about best steady state. Never stopping or idling. That practice is the real challenge: maximum load against minimal fuel burn. Against compromising reliability & longevity.

Driving empty is the wasteful mile. No work being performed. No revenue. Screwing off by driving around and burning gasoline. All sorts of ways thru the emotional impasse.

Being ABOVE 20-mpg IN TOWN ONLY with a loaded one-ton didn’t happen automatically.

My 30-something son always thought I was slow thru traffic. Until he noticed it more about being friction-free. Tires and brakes just don’t wear out (well past 100k miles service).

MPG is only a marker against operator efficiency. A check.

Out on the road we make fun of other truck drivers across the CB who only have one speed. Can’t adapt to conditions changes. Get thoroughly riled when this is stymied. The problem is emotional. We usually jab and gig them about safe operation. It’s almost the same as MPG.

No one much cares I can hit 11-mpg with an empty 35k lb rig. It’s being able to hit 9-mpg with from 30-40k in the box that matters. Your family’s welfare is the same. You MUST have a performance benchmark for the day it matters. Vacation or evacuation. And it won’t happen without experience (In the same way that commuting IS NOT adequate preparation for highway travel).

What’s the percentage change? What is the fuel cost per mile?

Careful about rejection: That’s the same “you” claiming loading your vehicle to near max is unrealistic. . Before the cock crows thrice. It’s quite the opposite.

“All my pistol range practice reproduces life’s guarantee of ALWAYS 10-yard shots under duress” Is what I “read” about the MPG claims on this forum. Pretty well worthless.

Get the baseline.
And then make Economy a norm.
Norm = Predictability.
(“Under any conditions encountered”).
Fuel is only one part.


.

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Last edited by slowmover; 05-22-2019 at 05:22 AM..
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