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Old 02-09-2014, 06:31 AM   #1
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Approaching hills, technique?

So I've pretty much nailed most hypermiling techniques now, but one thing I still struggle with is hills! Living in rural Wales, there are thousands of hills, some steep, some not so, they can really slow you down and ruin any attempts to save fuel.

So these are my choices:

1. Maintain speed (60 MPH) gently squeeze the throttle as the hill gradient increases, change down if need be.

2. Build up speed (70 to 80 MPH) before the hill and gradually let the speed drop as you go up the hill so you get the accelerating done before the hill.

3. Select a low gear, lower speed, and although the revs will be higher, you'll only be feathering the throttle.

Any other ideas? Going down the hill counteracts the fuel usage on the way up a little, I usually put the car in neutral and let gravity and the roller coaster effect do it's thing! This is the Dinas pass just up the road from me, it's very steep and very long and some trucks crawl up at 15 MPH!

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Old 02-09-2014, 10:09 AM   #2
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Most vehicles do best when you allow some speed to bleed off coming up the hill.
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Old 02-09-2014, 01:59 PM   #3
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So maintain normal speed, but ease off as you go up the hill? Wont the car slow too much and cause you to change down and/or accelerate harder again?
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Old 02-09-2014, 04:12 PM   #4
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Funnily enough, coasting in neutral downhill is a bad thing for three reasons that I can think of:
1I believe it's illegal
2 you lose engine braking and the vehicle won't handle so well
3 by coasting the engine will be running on tick over thereby using fuel. By leaving the vehicle in gear the injection system won't let any fuel in until just above tick over. To confirm this try going along a flat bit of road in say third then take your foot off the pedal and let the car slow down naturally. You should find that just above tick over there will be a bit of a surge, which is the injection system kicking in again to stop the engine from cutting out

Hope that's of some use
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Old 02-09-2014, 05:26 PM   #5
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Quote:
Originally Posted by Piair View Post
3 by coasting the engine will be running on tick over thereby using fuel. By leaving the vehicle in gear the injection system won't let any fuel in until just above tick over. To confirm this try going along a flat bit of road in say third then take your foot off the pedal and let the car slow down naturally. You should find that just above tick over there will be a bit of a surge, which is the injection system kicking in again to stop the engine from cutting out

Hope that's of some use
This is an oversimplification of Deceleration Fuel Cut Off (DFCO). Unfortunately, it is neither as universal nor as dependable as we all like to think. Each vehicle has different DFCO behavior; some do it pretty readily while others will find any excuse to delay or avoid it.

However, in this particular situation it should be pretty dependable -- assuming Draigflag is driving his 2009 Abarth 500, not his 1989 Fiat 126 BIS.

Anyway, given that I'm driving a sufficiently modern fuel injected vehicle I like to use heavy throttle in a high gear to get up the hill while minimizing pumping loss and maximizing BSFC, then DFCO down (being careful not to disturb DFCO by shifting, letting RPM fall too much, stepping on the accelerator, etc). It's the most fuel-efficient strategy I know and it helps keep my speed steady too.
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Old 02-09-2014, 10:53 PM   #6
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Originally Posted by theholycow View Post
Unfortunately, it is neither as universal nor as dependable as we all like to think. Each vehicle has different DFCO behavior; some do it pretty readily while others will find any excuse to delay or avoid it.
I experience this too: my '99 Yaris is the 'pretty ready' kind, often goes into DFCO even with a cold engine. Teresa, my BMW F650CS is the other, so engine braking is generally a bad idea with her if you can coast (engine braking means above idle revs, so quite possibly higher consumption than letting it idle).

Usefulness of DFCO depends on many things anyway: a light vehicle with bad aerodynamics (like a motorcycle) might need a steep descent just to keep its speed while coasting down. Add a relatively big engine and you get serious engine braking (loss of precious momentum) if you try DFCO there.

On the other hand, a heavy truck might have to use friction brakes on the top of DFCO. And a regular car might do just right with DFCO. All at the same place.

On the Draigflag's question - I still don't know after 5 years of trying to hypermile and a year of FCD watching. I suspect that letting a car slow down uphills can help, as long as you don't have to shift back. Backshifting seems to increase consumption instantly. Building up momentum before the hill may or may not help. One thing I believe I observed is that going faster uphills is 'cheaper' than doing so on a level road (may be the better BSFC?). Especially if you can get a longer coast in return after the crest.

With the car I often use a 3-phase approach too: let it slow down uphills (while in 5th), coast until it has 'enough' speed then DFCO to moderate speed. It might not be the best possible, though.

When motorcycling, I just keep speed in the highest gear going up then coast (or P&G if it's not steep enough) downhills. I only use engine braking when the road is really too steep for its curves or it's heading towards something nasty like a T junction.

Sorry if I couldn't help
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Old 02-10-2014, 12:04 AM   #7
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Coasting is safe, after al everyone "coasts" thousands of times per journey whilst changing gear! I've been doing it for years now and it's far more efficient than the fuel cut off method as you travel further and faster than when in gear. On the hill you see above, it's possible to travel 6+ miles in neutral. It's just getting up the hill, that's the difficult part. As alvaro says, perhaps it's better to get over the hill as quickly as possible!
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Old 02-10-2014, 06:30 AM   #8
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Originally Posted by Draigflag View Post
So maintain normal speed, but ease off as you go up the hill? Wont the car slow too much and cause you to change down and/or accelerate harder again?
Don't ease off, but don't increase throttle to maintain speed. If the grade will slow the car down, let it. It's a variation of driving with load. Naturally, the specifics of the road and trip will affect exactly what you do.

For the steep hills on my commute, I do this. Speed up and then DWL up the hill. I'll likely have to add throttle when the speed gets too low.

As to DFCO vs. neutral, it also depends on how much engine braking DFCO provides and whether you need or not.
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Old 02-11-2014, 12:07 PM   #9
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Another stretch 10 mins from my house, great on the way down, but a real fuel gulper on the way up!

https://maps.google.co.uk/maps?q=tal...bp=12,230,,0,0
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Old 02-11-2014, 09:45 PM   #10
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...but it's at least beautiful!
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