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      A Few Simple Rules   05/22/2017

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Dabnis2

Gas mileage

23 posts in this topic

This is for Mikewoff, or other scientific experts. So, east of Winnemucca, Nevada is Golconda Summit on I-80. The climb starts at about 4,300 feet, runs about 5 miles of about 5% to 7% grade to the summit, at about 5,200 feet  & about the same configuration back down to about 4,300 on the east side. Unless you get boxed in behind a truck it can be pulled in top gear, & brakes are not needed on the down side.

Would your mileage be the same if the route had no climb & descent?  Car would be a gasoline powered 2006 Honda Accord, not a hybrid, with an automatic transmission, speeds running about 65 MPH, both up & down.

 

 

       

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22 minutes ago, Dabnis2 said:

This is for Mikewoff, or other scientific experts. So, east of Winnemucca, Nevada is Golconda Summit on I-80. The climb starts at about 4,300 feet, runs about 5 miles of about 5% to 7% grade to the summit, at about 5,200 feet  & about the same configuration back down to about 4,300 on the east side. Unless you get boxed in behind a truck it can be pulled in top gear, & brakes are not needed on the down side.

Would your mileage be the same if the route had no climb & descent?  Car would be a gasoline powered 2006 Honda Accord, not a hybrid, with an automatic transmission, speeds running about 65 MPH, both up & down.

 

 

       

If the distance remained the same,  altitude and temperature would be the next variables.    Thin air, or thick air and more AC.   

 

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Just now, Lark said:

If the distance remained the same,  altitude and temperature would be the next variables.    Thin air, or thick air and more AC.   

 

Assume the test was done on the same day, back to back, temps not cooling much for the climb from 4,300 to 5,200 feet. & that barometric pressure was about stable for both runs. I am wondering if the "Free ride" down hill would compensate for the extra power needed for the uphill climb? IIRC, reading the shop manual on my former Nissan Pathfinder, it said fuel was shut off to the injectors when the throttle was closed at 900 RPM, or more.

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For a given speed, rolling resistance will be the same going up and down as going flat. Likewise, air resistance will be the same up and down as going flat. After that it's all engine efficiency. Most engines are less efficient under a heavy load than a low load and the curve is nonlinear, so you'll likely give up net efficiency working it hard on the way up and then letting it idle on the way down.

Another factor: miles/gallon of road is different than miles made good per gallon. Going over a hill decreases miles made good. 

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I think it might be more true in a manual transmission.   Fluid coupling would lose efficiency as the automatic transmission fluid became heated and lost viscosity on the uphill climb.   The difference would be small though.   

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1 minute ago, IStream said:

For a given speed, rolling resistance will be the same going up and down as going flat. Likewise, air resistance will be the same up and down as going flat. After that it's all engine efficiency. Most engines are less efficient under a heavy load than a low load and the curve is nonlinear, so you'll likely give up net efficiency working it hard on the way up and then letting it idle on the way down.

Another factor: miles/gallon of road is different than miles made good per gallon. Going over a hill decreases miles made good. 

Good point on peak efficiency rpm, more true for Diesel engines if I recall and an advantage of a hybrid.   So this would make the mountain trip less efficient then the Kansas trip of equal distance traveled.   

Miles made good seems irrelevant, if you go by odometer miles not miles as a bird flies.   If you flatten the hypotenuse the distance between points increases to compensate.   

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1 hour ago, Lark said:

I think it might be more true in a manual transmission.   Fluid coupling would lose efficiency as the automatic transmission fluid became heated and lost viscosity on the uphill climb.   The difference would be small though.   

Our earlier Accords had a "Lock up"  feature in top gear, supposedly  eliminating any torque converter slip. Our present 2006 Accord & 2014 CRV will, almost undetected, shift down a very slight amount from top gear when just a small amount of load is applied. I suspect the route with a climb & coast would consume more fuel than the equivalent flat route, temp, & atmospheric pressure being the same?

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1 hour ago, Lark said:

Good point on peak efficiency rpm, more true for Diesel engines if I recall and an advantage of a hybrid.   So this would make the mountain trip less efficient then the Kansas trip of equal distance traveled.   

Miles made good seems irrelevant, if you go by odometer miles not miles as a bird flies.   If you flatten the hypotenuse the distance between points increases to compensate.   

To Dab's point, miles made good matters point to point. If you're choosing between multiple routes between two points, flatter will get you there with fewer road miles. The most efficient mile is no mile at all. 

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Just now, IStream said:

To Dab's point, miles made good matters point to point. If you're choosing between multiple routes between two points, flatter will get you there with fewer road miles. The most efficient mile is no mile at all. 

Dabs needs to just get a bicycle, instead of driving to the Y.  

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15 hours ago, Lark said:

Dabs needs to just get a bicycle, instead of driving to the Y.  

Bicycles are dangerous:

 

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5 minutes ago, Dabnis2 said:

Bicycles are dangerous:

 

So is sitting in a car.   

IMG_0183.JPG

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18 hours ago, IStream said:

For a given speed, rolling resistance will be the same going up and down as going flat. Likewise, air resistance will be the same up and down as going flat. After that it's all engine efficiency. Most engines are less efficient under a heavy load than a low load and the curve is nonlinear, so you'll likely give up net efficiency working it hard on the way up and then letting it idle on the way down.

Another factor: miles/gallon of road is different than miles made good per gallon. Going over a hill decreases miles made good. 

Yup. Engine efficiency is tied to load and rpm, combustion time, temperature, turbulence.

An efficient all-electric vehicle with perfectly efficient regenerative braking (i.e. Coupled to a supercapacitor which then trickled to the batteries) and a constant speed with no energy lost to brake pad heat, would be nearly the same mileage for mountainous versus flat, assuming a round trip with no overall change in altitude. (A Nissan Leaf or Tesla is pretty close to this efficient.)

But in a regular vehicle, you end up using your brakes a bit coming down the mountain, your speed usually increases more down the mountain and your efficiency is lost in the brake pads and air resistance. Plus, like you wrote, a gasoline engine running at lower RPM like in Kansas, will usually run more efficiently (i.e. longer combustion time per stroke and thus more complete burn) than a a high RPM slog up the side of a mountain at 11,000 feet with thin air and thus a less-than-stoichiometric burn.

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The real question is: How did he get through Winnemucca, NV w/o getting pulled over by the HWY Patrol, and given a ticket for A: Unsafe driving. B: Failure to maintain a lane. C: unsafe speed for conditions. or D: Failure to signal a lane change.

The only way Winnemucca gets any "tourist business" is because the state cops terrorize people into pulling off I-80 for a meal at their wives' restaurants.

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4 hours ago, Lark said:

So is sitting in a car.   

IMG_0183.JPG

How true, We just returned from another delivery trip to our top selling gallery, about 60 miles north of us, lots & lots of oncoming traffic on a fairly narrow, twisty two lane road. Kind of like looking down the muzzle of a shot gun each time a car or truck goes by. Fortunately, there were not many bicycle riders, not sure why, maybe too hot for them?

Yes, looking at your chart, I probably died a bit over the last 4 or 5 hours, sitting in the car. Life is hazardous, especially on a bicycle. 

"Look out!!!, Splat!!!, Damn, another dent in the car" "Oh my, look, he is still squirming, maybe we should  go back?"

"No, you say, it will make us late for the Senior's Barbecue?"  "Got it, hammer down, somebody else will move him off the road" 

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4 hours ago, mikewof said:

Yup. Engine efficiency is tied to load and rpm, combustion time, temperature, turbulence.

An efficient all-electric vehicle with perfectly efficient regenerative braking (i.e. Coupled to a supercapacitor which then trickled to the batteries) and a constant speed with no energy lost to brake pad heat, would be nearly the same mileage for mountainous versus flat, assuming a round trip with no overall change in altitude. (A Nissan Leaf or Tesla is pretty close to this efficient.)

But in a regular vehicle, you end up using your brakes a bit coming down the mountain, your speed usually increases more down the mountain and your efficiency is lost in the brake pads and air resistance. Plus, like you wrote, a gasoline engine running at lower RPM like in Kansas, will usually run more efficiently (i.e. longer combustion time per stroke and thus more complete burn) than a a high RPM slog up the side of a mountain at 11,000 feet with thin air and thus a less-than-stoichiometric burn.

That is what I thought, too, probably best to avoid climbs. When I was cross country skiing, it was fun to go downhill, but uncivilized to climb up there to go down, I think my Dad once told me: "There is no such thing as a free lunch", or something like that.

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1 hour ago, Mrleft8 said:

The real question is: How did he get through Winnemucca, NV w/o getting pulled over by the HWY Patrol, and given a ticket for A: Unsafe driving. B: Failure to maintain a lane. C: unsafe speed for conditions. or D: Failure to signal a lane change.

The only way Winnemucca gets any "tourist business" is because the state cops terrorize people into pulling off I-80 for a meal at their wives' restaurants.

Well, it has been a while since we went to Winnemucca, for a great Basque dinner at Ormachea's Dinner House. Actually, the Town is fairly busy, especially during hunting season, even though the freeway by-passes it. Years ago, before the  early 60's we traveled old Hwy 40 a lot, got to go through all the Towns, whether you wanted to, or not. The outskirts of both Winnemucca & Elko have lots of new homes, & is looking pretty good, perhaps because of a upswing in the gold mining industry? 

https://www.facebook.com/Ormacheas/

http://www.runamucca.com/

https://www.google.com/search?q=Run+-+a-mucca&source=lnms&tbm=isch&sa=X&ved=0ahUKEwirnq6Z8o7VAhVi3IMKHTynCbIQ_AUICygC&biw=1097&bih=534

 

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6 hours ago, mikewof said:

Yup. Engine efficiency is tied to load and rpm, combustion time, temperature, turbulence.

An efficient all-electric vehicle with perfectly efficient regenerative braking (i.e. Coupled to a supercapacitor which then trickled to the batteries) and a constant speed with no energy lost to brake pad heat, would be nearly the same mileage for mountainous versus flat, assuming a round trip with no overall change in altitude. (A Nissan Leaf or Tesla is pretty close to this efficient.)

But in a regular vehicle, you end up using your brakes a bit coming down the mountain, your speed usually increases more down the mountain and your efficiency is lost in the brake pads and air resistance. Plus, like you wrote, a gasoline engine running at lower RPM like in Kansas, will usually run more efficiently (i.e. longer combustion time per stroke and thus more complete burn) than a a high RPM slog up the side of a mountain at 11,000 feet with thin air and thus a less-than-stoichiometric burn.

The other part is fuel load. For example, in my diesel the engine is technically more efficient under burden since the turbo is assisting more, and the engine is designed to work under a significant load.

But I guarantee you at 55 mph up the hill, it'll be dumping in more fuel and creating more heat. Much of that heat is wasted energy. So in the end, flat would be more efficient because it's just not trying very hard.

The weird part is that it is VERY hilly by the cottage but I pulled 21.7 mpg over the last two weeks. I average 20.8 in the flatlands of IL.

This is what it looks like by the cottage so you can imagine the road grades.

15367976258_df7ca60c7f_b.jpg

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16 minutes ago, austin1972 said:

The other part is fuel load. For example, in my diesel the engine is technically more efficient under burden since the turbo is assisting more, and the engine is designed to work under a significant load.

But I guarantee you at 55 mph up the hill, it'll be dumping in more fuel and creating more heat. Much of that heat is wasted energy. So in the end, flat would be more efficient because it's just not trying very hard.

The weird part is that it is VERY hilly by the cottage but I pulled 21.7 mpg over the last two weeks. I average 20.8 in the flatlands of IL.

This is what it looks like by the cottage so you can imagine the road grades.

15367976258_df7ca60c7f_b.jpg

Interesting, are the lake & the flatlands at about the same elevation? Although, I would think the turbo might compensate for elevation  changes? Is it cooler at the lake? If my math is correct,  that is about a 5% mileage gain at the lake, which I think is fairly significant, assuming your speeds are about the same.

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Diesels are different.

 I drove a diesel across Canada, and fully loaded (Probably over loaded) I got 45 MPG from Quebec to somewhere outside of Medicine hat..... Then it started creeping down. By the time I hit the tip of the rockies I was getting 27MPG. I got about 35 MPG on the backside blowing black smoke the whole way down to Hope, B.C. From there to Seattle I got back up to about 40MPG. From Seattle to Ft. Bragg I got a little better, but shortly after that I blew a timing chain, and that was a bitch.

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A worn timing chain is a Bad Thing on a gas engine but at least it'll run okay for a long time, albeit with reduced power. The same amount of wear will fuck a diesel far more thoroughly and far faster.

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12 hours ago, Dabnis2 said:

Interesting, are the lake & the flatlands at about the same elevation? Although, I would think the turbo might compensate for elevation  changes? Is it cooler at the lake? If my math is correct,  that is about a 5% mileage gain at the lake, which I think is fairly significant, assuming your speeds are about the same.

Almost exactly the same elevation. The ice age made sure of that. ~600 feet above sea level (Lake MI is 577 and the farm is 606).

It is cooler at the cottage as it's 4 degrees north of the farm.

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57 minutes ago, austin1972 said:

Almost exactly the same elevation. The ice age made sure of that. ~600 feet above sea level (Lake MI is 577 and the farm is 606).

It is cooler at the cottage as it's 4 degrees north of the farm.

Very interesting, indeed. I wouldn't think a temperature change, unless it is significant, would result in a 5% improvement, but the numbers don't lie. Perhaps a different source of fuel?

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13 hours ago, Mrleft8 said:

Diesels are different.

 I drove a diesel across Canada, and fully loaded (Probably over loaded) I got 45 MPG from Quebec to somewhere outside of Medicine hat..... Then it started creeping down. By the time I hit the tip of the rockies I was getting 27MPG. I got about 35 MPG on the backside blowing black smoke the whole way down to Hope, B.C. From there to Seattle I got back up to about 40MPG. From Seattle to Ft. Bragg I got a little better, but shortly after that I blew a timing chain, and that was a bitch.

Had a VW Rabbit diesel, used to get about 45 MPG on the highway. All of a sudden it got 35 MPG. Just before I got the wrenches out, I remembered I put the ski rack on & left it on. Took the ski rack off, right back to 45 MPG. That engine had a timing belt. The shop manual was adamant about changing it at 60,000 miles, which I did twice. IIRC, the manual warned of "Substantial" damage if the belt were to break.

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