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Old 07-15-2008, 08:51 AM   #31
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Go ahead and use the cruise for the flat areas. When you come to a hill, click it off and use your foot to drive up and over and down. Then turn it back on.

I find that the CC wants to downshift one or even two gears for the smallest hills. You don't want that. I can maintain speed AND keep it in top gear with my foot. It's just a matter of seeing what's coming and anticipating. The computer can't do that - it can only react to what's already happening.
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Old 07-15-2008, 10:53 AM   #32
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Originally Posted by lowbridescape View Post
It's the V squared part. Drag is proportional to velocity squared.
It's a power dependence then.
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Old 07-15-2008, 08:51 PM   #33
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Uhm...no. It's speed dependent.

Aerodynamic drag is proportional to the square of the velocity. Double the speed, whether pushing up a hill or coasting down, drag will increase by a factor of four.

However, the issue of hills is way more complicated than just looking at drag because you have the non-proportional effects of gearing and its effect on engine efficiency (keep it in high gear or bust), speed limits and law enforcement (which tend to screw up otherwise pristinely pure physics), road conditions (best fuel economy will be achieved just before you hit the bottom of the cliff, at which point it goes to zero), etc.

So you need a strategy. Mine is to hit the bottom of the hill just fast enough not to aggrevate the local constibalry, hold as much power as possible without downshifting for as long as possible and let the speed bleed off. The inefficiency of my Escape going up a hil in a lower gear completely outweighs the drag issue. And that's on a car affectionately called The Brick due to its complete lack of aerodynamics.
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Old 07-16-2008, 07:38 AM   #34
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Hills.

I do an easy 25% acceleration about the first 1/4 to 1/3 down, coast the rest of the way until I am near the bottom, then "accelerate" with about 25% throttle, but gradually backing off as I am going up the hill. I don't try to maintain speed up the hill, but I do slowly decrease speed on the way up.

Cruise control will give you the worst fuel economy with even the small hills or overpasses. Cruise control wants to maintain speed by accelerating up the hills, whereas you really want to back off the accelerator on the hills, then maintain that slower speed over the top, then light acceleration on the downside to get back up to speed.

IMHO
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Old 07-16-2008, 01:03 PM   #35
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lowbridescape and 99 Metro, we share the same hill philosophy. IMHO it is much easier on the engine to get a little burst of speed using gravity to assist you and let inertia carry you over or assist in getting you up the hill.

Gravity, not just a good idea, it's the law.

I didn't realize this would get this deep when I asked the question. It's cool to talk to people as interested in fuel economy as I am. According to my wife we are special group with a special name, "dorks" is what she calls us! But I tell her we're dorks with more money in our pockets.
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Old 07-16-2008, 01:15 PM   #36
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Old 07-16-2008, 04:51 PM   #37
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Quote:
Originally Posted by lowbridescape View Post
Uhm...no. It's speed dependent.

Aerodynamic drag is proportional to the square of the velocity. Double the speed, whether pushing up a hill or coasting down, drag will increase by a factor of four.

However, the issue of hills is way more complicated than just looking at drag because you have the non-proportional effects of gearing and its effect on engine efficiency (keep it in high gear or bust), speed limits and law enforcement (which tend to screw up otherwise pristinely pure physics), road conditions (best fuel economy will be achieved just before you hit the bottom of the cliff, at which point it goes to zero), etc.

So you need a strategy. Mine is to hit the bottom of the hill just fast enough not to aggrevate the local constibalry, hold as much power as possible without downshifting for as long as possible and let the speed bleed off. The inefficiency of my Escape going up a hil in a lower gear completely outweighs the drag issue. And that's on a car affectionately called The Brick due to its complete lack of aerodynamics.
The number "2" you see near "v" is called a power, that's what meant.
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Old 07-16-2008, 06:13 PM   #38
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We are debating hill strategy, but the strategy depends on the hill.

Most hills around here are actually ancient drainage pathways, they start downhill and then you go uphill. Elevation changes are rarely more than a typical interstate overpass, but in reverse.

I approach then at my normal speed, coast in neutral down the hill and gain some speed, then let it coast uphill until its about 5 below my desired speed, then use top gear to get the rest of the way uphill.

One one particular hill it takes .6 mile from initial coast to final climbing of the upslope, with only .1 mile of the .6 where I actually have any engine power applied to the drivetrain. I don't EOC so for 80% of the distance I am idling at .2 gal per hour. Thats at 50 MPH average speed.

Hill country strategy totally depends on the grade you are dealing with. The slight grades I have here are actually beneficial to fuel economy, meaning I can actually get better mileage than I can on flat ground.

Hill climbing will get your brake specific fuel consumption at a much better point in your Map, the energy required to climb the hill (when it is like the ones I deal with) allows me to not have to downshift.

In fact coasting on almost every downhill slope on the shallow grades here is one of my basic strategies for better mileage, combined with drafting, and DFCO. those 3 tactics are almost all of my hypermiling efforts. The only additional one is some P&G on roads with speed limits of 45 MPH and below.

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Old 07-16-2008, 06:22 PM   #39
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The number "2" you see near "v" is called a power, that's what meant.
Sorry. Misunderstood. I think of it as an exponent.
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Old 07-16-2008, 06:26 PM   #40
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My wife calls me all kinds of names.

You are a moron because you sold your business and aren't getting a paycheck!

When we sold the house that I built, for $165,000 more than it cost to build, I let her take the check to the bank. At one point it was appreciating $525 a week.

You paid $3000 for a wrecked car, you havent even looked at in person!

It will be painted tomorrow, 7000 miles at 58.83 MPG, almost 35,000 on the odometer today. I have a total of $5000 cash in the car and some sweat equity, about the cost of a hybrid battery for 200,000 miles of transportation.

You bought another lot!

The house sitting on that lot is now appraised at $140,000 more than it cost me to build, and we owe no one a dime, except for monthly bills.

Every once in a while she tells her two daughters she is thinking about moving out. They tell her to take a pill and have a glass of wine...............


..........It goes on Judah...................................

regards
gary
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