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Old 11-11-2015, 01:28 AM   #11 (permalink)
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Originally Posted by Fat Charlie View Post
And letting the downhill carry you for free helps, too.

Burning gas to force the car downhill, which gravity is already doing for free, isn't very economical.
It seems to be one of those things where you can argue it either way. The only way to be sure is to test it. I don't have a scan gauge but I can get some idea from the standard instrumentation on the car. I'll check it on some trips in the next few weeks and see what I find out.

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Old 11-11-2015, 09:06 AM   #12 (permalink)
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Actually, you can't. But tossing around ideas is something else entirely.

Back when I started, I tried to roar up a hill to start my glide as soon as possible- maximizing glide distance seemed like the right thing to do. I did a lot better when I started working with the hills instead of against them.
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Old 11-11-2015, 09:57 AM   #13 (permalink)
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Originally Posted by SDMCF View Post
It seems to be one of those things where you can argue it either way. The only way to be sure is to test it. I don't have a scan gauge but I can get some idea from the standard instrumentation on the car. I'll check it on some trips in the next few weeks and see what I find out.
I suggest you get one, or an equivalent tool like Ultragauge or bluetooth obd adapter and smartphone app (torque is one).

You don't want to go too fast or aerodynamics start working against you. You don't want to go too slow or you'll have to drop a gear or two and that costs a lot of fuel. We all have to work with traffic around us so a more steady speed is better for everyone, not just you.
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Old 11-11-2015, 09:57 AM   #14 (permalink)
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Everyone here is debating hill strategy.

The size of the hill is the determining factor and there is no STANDARD with which to compare.

You have both grade and length to consider and even more when you start looking at the terrain beyond the first hill.

I accelerate both uphill and downhill.

The perfect grade allows you to load the engine to it's highest efficiency when climbing the hill, then coasting downhill with the engine off, WITHOUT ANY CHANGE IN SPEED, WHICH ELIMINATES THE ADDITIONAL DRAG WHEN VELOCITIES INCREASE.

Downhill is NOT free, you paid for it uphill.

Less than the perfect grade or more means compromising your tactics.

With less you might P&G both uphill and downhill.

With more you should consider DWL and gradually losing speed in the climb so the highest speed downhill is not ticketable.

The best way to determine the best tactic is to test the downhill portion to determine how close it is to the perfect grade FOR YOUR CAR and its total drag, resisting your desired perfect coast that is continuous for that grade.

That "perfect" grade for YOUR car will not be perfect for MY car.
That "perfect" grade changes with the weather and season.

I have coasted downhill on the mountain near Virginia Tech and at 85 MPH I had to shift into gear to slow down to keep from ramming a big rig. That same grade without the big rig would be a 70mph max coast.

Every scenario is different, but one rule that I consider absolute is trying to a avoid high speeds and the exponential increase in drag, to say nothing of the lower incidence of court appearances.

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Old 11-11-2015, 10:08 AM   #15 (permalink)
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When you have the advantage of experience in driving any particular sequence of hills or mountains, then you need to start thinking backwards.

Start at the end and work your way back to the beginning, determining your speeds at various points in the climb-descend sequence.

In much the way the designer of a roller coaster uses grades and overall grade to determine his speed through the system the hypermiler determines his best tactic for best mpg within his average speed target.

Rolling hills without outside traffic influences are about as good as it will ever get for mpg.

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Old 11-11-2015, 01:44 PM   #16 (permalink)
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Originally Posted by Fat Charlie View Post
Actually, you can't.
Sorry, I don't follow. I can't do what?

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I did a lot better when I started working with the hills instead of against them.
To my mind, that is what I am doing. My engine is working more when it is getting assistance from the hills, and working less when it has to battle against the hills.
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Old 11-11-2015, 01:46 PM   #17 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
You don't want to go too fast or aerodynamics start working against you. You don't want to go too slow or you'll have to drop a gear or two and that costs a lot of fuel. We all have to work with traffic around us so a more steady speed is better for everyone, not just you.
I don't know why you seem concerned about me going too fast or too slow. What makes you think I am likely to do either?
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Old 11-11-2015, 01:47 PM   #18 (permalink)
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Originally Posted by Old Mechanic View Post
Rolling hills without outside traffic influences are about as good as it will ever get for mpg.
I totally agree. Fortunately almost all of my driving is like that.

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