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!

https://upload.wikimedia.org/wikipedi..._Maesglase.jpg

Most vehicles do best when you allow some speed to bleed off coming up the hill.

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?

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

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.

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 :o

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!

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.

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

...but it's at least beautiful!

Yes it is a beautiful part of the World with some amazing driving roads. Worth using a bit of fuel for! The fact that there's very little traffic means you can usually drive as quick or as slow as you like and not hold anyone up!

Very beautiful! Going uphill I would think using highest gear and throttle up to 90% is the most efficient as long as you don't slow down too much and have to change gear. Then it is better to choose that gear from the beginning of the steeper slope if you can predict that.

Downhill depending on how steep it is at the moment i think alternating between coasting and engine braking in highest gear to restrict speed is best.

This is exactly what I do. I tend to get best MPG #'s when driving in mountainous areas.

Avoid downshifting unless absolutely necessary.

That's what I tend to do, but it seems to really drink the fuel. I guess there's no avoiding it. I find neutral is best as the engine braking slows you down too much, and you need to accelerate sooner, which uses more fuel than idling in neutral.

I guess it's not the same with all cars. Even with multiple climbs at near full throttle, I always see 40+ MPG at speeds of 55 MPH & under. 65-70 MPH in the mountains drops the numbers back to 40 if I maintain speed on the inclines.

It depends on the specifics of the hill and car. On my commute, I consider it good to get 20mpg while climbing the big hills when I had the HHR and Ranger. The Sonic does a little better. All being automatics limits my options, but the gen2 Prius could only manage 25mpg on the same incline.

Been practising a bit. It is a little upsetting seeing the trip MPG dash readout drop on every hill, on a hill I regulary climb, I see it drop from 47 MPG to around 42 MPG, but by the time I get home its avereaged out at around 50 MPG. I tend to stay in top gear and accelerate gently up the hill with as much throttle as the car needs. Theres a sweet spot in the throttle where the turbo provides enough power to pull up the hill at the speed limit, but as not to use much fuel.

Every cloud had a silver lining, although it uses fuel going up, the car uses almost no fuel going down so the incline/decline kind of counteract each other. I'm happy with 50 MPG, the official average for my car is 42 MPG so I should not complain!

There's no need to feel bad when the number drops as you climb the hill. Think of it as an investment. You're making energy as efficiently as you can and storing it in the car's mass, then you'll use the stored energy later when you would not be able to make it as efficiently.

Your car may be entering DFCO going down the hill, and actually using no fuel.

Well I do put the car in neutral going downhill. I appreciate the fuel cuts off if you leave it in gear, but I find the engine braking slows you down, and the need to accelerate again comes sooner in gear. But in neutral, yes it uses a bit to idle, but you can go 2 or 3 times further just on gravity. I've practised this technique and it works well.

Hi all,

I've had some success with my car.

There are no mods on the car, except for the new cruise control.

The only thing I have done is to turn off the air con.
I have 15" wheels which were set at the higher pressure as listed in the back of the diesel filler cover.

I regularly average 68-70mpg and have got 82mpg on a couple of occasions.

As for driving style I am a believer in the clutch down technique while coming up to roundabouts, red traffic lights and stationery traffic all at slow speeds.
I suppose both of my high mpg top scores were possibly due to very big hilly journeys through the Cairngorms and Lakes?

I suppose this is a form of cheating as the car will be in idle for short spaces of time. When I wasn't trying this technique fully I was getting 65-68mpg.
Though it's interesting how much extra you can get by "coasting".

When the wife does the school run the best she got (though she couldn't give a crap about mpg) was 52-55mpg though that was only a couple of times and she had the air con on and the car needed a service.
The other thing was that I added the redex diesel additive.

Though the last 4 fill ups have lead me to believe it only adds 4mpg to my overall score. Not sure if the extra cost in buying redex is beneficial for that extra mpg.

https://badges.fuelly.com/images/sig-uk/256133.png

Hi there. Im a self confessed coaster too, like I said earlier, there is a long down hill section locally that I can coast 6 miles down, using very little fuel indeed. I have found if I set my cruise control to 60 MPH the car will accelerate up the hill and maintain 60, but not sure what the effect on fuel consumption is. Its the uphill thats the killer!

You wanna increase speed as your going downhill. by using gravity for free energy!!
Never ever accelerate going up in a hill! just use the energy that you have to go up the hill with taps of light accelerations!!
Put the car in neutral when you are going downhill!!

Never use Cruise control on hills!!! the engine will brake going downhill and accelerate going uphill!!

I always use neutral going down. When watching the range reading, I can loose about 70 miles going up some steep hills. On the way down, that range can then go back up by about 50 miles in neutral.

Hills really do suck. There's a good long one which kills my commute home, shaves probably a good 2-5mpg off of the whole thing. Then again, the alternate routes are even worse.

It's long and relatively shallow, but it's right after a dead stop. I generally utilize low-mid throttle to get up over it and then maintain that throttle until I reach the PSL, at which point I back off. I tried muscling up the hill and reaching PSL much sooner (which also gets me into top gear and TC lockup sooner), and the results were dismal.

Otherwise, as stated, I try to use my momentum. Bleed speed up the hill, coast and/or gain speed back down it depending on what comes after the hill.

Thanks for the tips, I too see 5 to 7 MPG drop off my average on some hills, still haven't nailed a technique yet! I was considering using cruise control, set it at say 50 or 55 and just let the computer use just the right amount of fuel to get up and over the hill.

In my experience, the cruise control doesn't do a stellar job. It'll let the speed drop then aggressively adds power to re-accelerate - uphill. Newer cruise controls might have some better logic, though. Newest car I have had with cruise was a 2004.

You should judge your speed over the crest of the hill based on how steep the downhill side is. If you can coast in neutral without gaining or losing speed, then it doesn't matter what speed you top the hill at, because in neutral you'll just stay at that speed. If you can gain speed while coasting on the downhill side, you should slow down as you approach the top, so that you don't waste energy maintaining speed that you just have to throw away with the brakes on the downhill side. If the hill is not steep enough to maintain speed in neutral, I like to accelerate over the hill and then coast as long as I can without holding up traffic behind me. In a similar manner to pulse and glide, except with longer glides. (I'm not really a fan of pulse and glide in practice, except on hilly terrain).

On a hill of the proper slope, sometimes you can actually use less gas to get over it than you would driving the equivalent distance on flat ground. This is because gasoline engines are increasingly efficient at increasing load (not increasing revs -- increasing throttle). If you can climb the hill without downshifting, and then coast in neutral all the way down, you store up all that energy at higher efficiency (full load) and once you reach the top, coast in neutral all the way down and you don't pay the internal engine friction of driving at cruising revs.

It costs gas to keep the engine running at idle, but it costs less in gas to run the motor at idle speed than it costs you in momentum keeping the car in gear and spinning the motor at 2,000+ revs. Hence why you shouldn't necessarily coast in gear unless you need to bleed speed off, or unless you know there's a stop light or obstacle at the bottom of the hill. (Or, if it makes you feel unsafe or uncomfortable.)

Of course this doesn't go for diesels, because diesels are the opposite (decreasing efficiency at increasing load).

Almost all of my best tanks have been on hilly road trips through the rural parts around here.

I always go in neutral down hills, some are so steep that I let the car speed and go over the speed limit by 10 or 15% (i dont speed that often anyway) and the more speed the car gathers, the longer it will last once flat ground has been reached. Your comment about diesels, diesels are more efficient when idling are they not? You can leave diesels running all night like a generator and they dont use much fuel, so I assumed they are pretty effecient when idling.

I always think of it this way. If you ever feel your engine start to bog down a little its running richer, so there is a little gas that is not getting used to its fullest potential. That is not a fact. That is how I justify my actions. I get my best mpg on hills because I don't use my cruise control. I usually feather the throttle the entire time. I keep the engine running lean as I can while still slightly accelerating downhill, so I can slightly decelerate going up the next hill. I usually maintain speed at the base of a hill and then the more I get up the more I'll let off to keep the engine running lean as the rpm's drop. By the time I get to the top my gas petal is at or around its highest point in the cycle and I repeat. Works good for me!

I never understood the point of coasting in neutral unless maybe its on your final hill or two before a stop. Your engine is still running and you still have drivetrain friction since the drive wheels are connected to the transmission all the time. It seems like your paying for a slight increase in mpg with drivetrain stress from the extra shifting from neutral to high gear. I guess I like my car too much. There is also the consideration here that the more your speed fluctuates, the more you will lose to air drag at the bottom of the hill. If you feel your car begin to near terminal velocity in Georgia overdrive, its a good indication you could be doing a little better. Just my humble opinion. I don't have the computers to back it up, and my newest cars have historically been about 15 years old.

You just about perfectly described the "Driving with load" technique, and it is VERY effective on hills.
Vehicles with electronic fuel injection will shut down the injectors (Fuel Cut) and engine brake if left in gear. This is fine on steep hills, but on more gradual hills, you can either idle the engine and coast in Neutral, or leave it in drive and hold your foot on the throttle. Personally, I use all of the techniques you describe (Driving With Load, Neutral Glide, and Fuel Cut) depending on my speed, incline of hill, traffic, and whether I intend to speed up, or slow down.

Thanks for the input. Recently I have been trying the exact technique you described, being gentle, and not accelerating hard but progressively. I try to keep the turbo just on boost, not so much that it's using too much fuel, but just enough to pull me up the hill. I still loose speed, that's the only thing as it's obviously a small car and some of these hills are pretty big, the only way to avoid loosing speed is to apply maximum throttle, but then that's a huge waste of fuel.

If you're doing DWL properly, you will lose speed going up hills.

So is it better be gentle and sacrifice a little speed when ascending a steep hill would you say?

Yes. let it bleed off speed, but just make sure you stay going fast enough to keep it in high gear. If you slow down enough for it to downshift, then you're using more fuel.

DraigFlag, I read somewhere that your best MPG tactic when approaching a grade is to maintain the same gas pedal push. Simply allow the car to slow down naturally on the upside of the grade.

I suppose, for the convenience of cars behind you, you can accelerate BEFORE the hill to maintain a reasonable amount of speed on the upside of the grade.

In other words, depressing the gas pedal on the upside of the hill IS the worst thing you could do to to MPG.

I tried that, and the hills are often too long and I gradually loose too much speed. Once I reach about 45 Mph, the gsi (gear shift indicator) tells me to change into 4th. So now I'm changing into 4th and feathering the throttle more using higher revs instead. Not sure if it's any more or any less efficient yet.