Sweetsixteen said:

When manufacturers calculate their claims for economy, they try every trick in the book, but they do not accelerate hard from one speed to the next during their tests. They use the maximum permitted time between designated speeds (check out the EU test specs), because they know that hard acceleration uses more fuel than gentle increases in speed.

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How in the world do you know how mfg's arrive at their test data?

''It's not commonly understood by people who drive,'' Dr. Dougherty said. ''They think that the way to get best fuel economy is to accelerate very gently, but that proves not to be the case. The best thing is to accelerate briskly and shift.

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http://www.nytimes.com/2001/06/07/t...d-miser-teaches-drivers-how-to-save-fuel.html

Talk about out baffling with BS!.

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I suppose a bit more won't hurt:

"Urban driving
The NEDC is composed of two parts: ECE-15 (Urban Driving Cycle), repeated 4 times, is plotted from 0 s to 780 s; EUDC cycle is plotted from 780 s to 1180 s
The Urban Driving Cycle ECE-15 (or just UDC) was introduced first in 1970 as part of ECE vehicle regulations; the recent version is defined by ECE R83, R84 and R101.[1][3][4] The cycle has been designed to represent typical driving conditions of busy European cities, and is characterized by low engine load, low exhaust gas temperature, and a maximum speed of 50 km/h.[5]
When the engine starts, the car pauses for 11 s - if equipped with a manual gearbox, 6 s in neutral (with clutch engaged) and 5 s in the 1st gear (with clutch disengaged) - then slowly accelerates to 15 km/h in 4 s, cruises at constant speed for 8 s, brakes to a full stop in 5 s (manual: last 3 s with clutch disengaged), then stops for 21 s (manual: 16 s in neutral, then 5 s in the 1st gear).
At 49 s, the car slowly accelerates to 32 km/h in 12 s (manual: 5 s in 1st gear, 2 s gear change, then 5 s in the 2nd gear), cruises for 24 s, slowly brakes to a full stop in 11 s (manual: last 3 s with clutch disengaged), then pauses for another 21 s (manual: 16 s in neutral, 5 s in the 1st gear).
At 117 s, the car slowly accelerates to 50 km/h in 26 s (manual: 5 s, 9 s and 8 s in the 1st, 2nd and 3rd gears, with additional 2 × 2 s for gear changes), cruises for 12 s, decelerates to 35 km/h in 8 s, cruises for another 13 s, brakes to a full stop in 12 s (manual: 2 s change to the 2nd gear, 7 s in the 2nd gear, last 3 s with clutch disengaged), then pauses for 7 s (manual: in neutral with clutch engaged).
The cycle ends on 195 s after a theoretical distance of 994.03 meters, then it repeats four consecutive times. Total duration is 780 s (13 minutes) over a theoretical distance of 3976.1 meters, with an average speed of 18.35 km/h.

Extra-urban driving
The Extra-Urban Driving Cycle EUDC, introduced by ECE R101 in 1990,[1] has been designed to represent more aggressive, high speed driving modes. The maximum speed of the EUDC cycle is 120 km/h; low-powered vehicles are limited to 90 km/h.[5]
After a 20 s stop - if equipped with manual gearbox, in the 1st gear with clutch disengaged - the car slowly accelerates to 70 km/h in 41 s (manual: 5 s, 9 s, 8 s and 13 s in the 1st, 2nd, 3rd and 4th gears, with additional 3 × 2 s for gear changes), cruises for 50 s (manual: in the 5th gear [sic]), decelerates to 50 km/h in 8 s (manual: 4 s in the 5th and 4 s in the 4th gear [sic]) and cruises for 69 s, then slowly accelerates to 70 km/h in 13 s .
At 201 s, the car cruises at 70 km/h for 50 s (manual: in the 5th gear), then slowly accelerates to 100 km/h in 35 s and cruises for 30 s (manual: in the 5th or 6th gear).
Finally, at 316 s the car slowly accelerates to 120 km/h in 20 s, cruises for 10 s, then slowly brakes to a full stop in 34 s (manual: in the 5th or 6th gear, lat 10 s with clutch disengaged), and idles for another 20 s (manual: in neutral).
Total duration is 400 s (6 minutes 40 s econds) and theoretical distance is 6956 meters, with an average speed of 62.6 km/h.

Combined
The combined fuel economy is calculated by a total consumption of urban and extra-urban cycles over the total distance (theoretical 11023 meters). The total test time amounts to 1180 s with an average speed of 33.6 km/h. Sometimes the NEDC is also quoted at 1220 s, which includes the initial 40 s with the vehicle at standstill and combustion engine off."



The expression 'slowly accelerates' - used throughout the test specification here - illustrates the point I made earlier that gentle acceleration is used by car manufacturers when squeezing maximum fuel mileage from their cars.

The rest, as has been said, is just BS!

Sweetsixteen said:

The expression 'slowly accelerates' - used throughout the test specification here - illustrates the point I made earlier that gentle acceleration is used by car manufacturers when squeezing maximum fuel mileage from their cars.

The rest, as has been said, is just BS!

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Thankyou for proving my point

The official test procedure requires the manufacturers to accelerate slowly. If you've seen a video of the testing being done the driver has to follow a trace on the screen exactly. It's not that they can take up to 8 seconds to get from speed x to speed y, but they must get to speed in that time, change gear as prescribed and so on. There's no point reaching top speed in 5 seconds, if all that means is holding high revs for another 3 seconds before the test procedure allows the driver to shift up.

If the test was indeed the most economical way to drive, the official figures would be impossible to beat. I've linked to a real world study where accelerating faster saved the participants fuel. The only arguments for accelerating slowly are based on the over simplified notion that more speed takes more power. Again no one is saying full revs, full throttle

At any rate the real world proof is at the bowser. If you beat the official numbers with your granny driving approach, let me know. I'll stick to my method that according to regular car forums doesn't work, yet apparently through magic beats the test cycle in the real world.

It is even as you say, oh great one!
Apparently, major car makers had a large input when this test spec was written up.
Speaks for itself really.
Happy driving.
Ciao.

Not sure why UFI's methods would be controversial. Makes sense to me. Accelerate and change up quickly so you use the higher gears sooner.

My Dualogic has an annoying tendency to hold on to the lower gears too long, so I often shift up using the paddles.

UFI, are you on Fuelly? Would be really cool to see your progress as your TwinAir is run in properly

I was a bit early for work today so I ran a test.

I found there's a valley near the river here and of course there's a hill on either side. There's a car park at the bottom. The hills are the kind I'd normally tackle in 2nd gear, so reasonably steep.

I know the roads well enough so I mentally mapped out a figure of 8 route, climbing the hill on each side and crossing past the carpark each time. I did three figure of 8 loops crossing the carpark a total of six times, stopping in the carpark every complete circuit to take a photo of my screen.

I'd driven 20k in the morning so everything was already up to temp.

My commute had recorded a convenient 6.00. This particular instrumentation doesn't seem to let you manually reset 'Short trip' so rather than wait for it to reset automatically, I left the 6.00 as my baseline.

Techniques used were just basic. Climb uphills at 100% load, coast in gear on the way down (I used the A/C and brakes to stick to the speed limit). The route involved corners, speed bumps, round abouts etc. It wasn't some carefully picked perfect run.

So up the first hill, of course, my Instantaneous consumption shot up on the climb. At the top of the hill I was now looking at 6.2X, get to the top of the hill, accelerate still at 100% load to a bit below the speed limit, then lift off fully and let gravity to the rest, turn on the A/C once up to the speed limit (hey it's free energy!), brake, roundabout, stop sign etc.

Across the carpark for the first time and we have a perfect 6.00

Up the other hill, again the meter reading around 6.2. Back down the hill (this one has speed humps in it so no choice but to use the brakes). Pull into my parking spot for the first time and, wait for, it another 6.0. This run was upset a bit by an SUV on the down hill stretch, I didn't want to get in their way too much so I did something you never should, accelerate on a decent :devil:

Second run (direction reversed), starting at 6.00, pulled into the parking spot after my figure of 8 and I actually came in at 5.8X!

Third run in the same direction as the first. Started at 5.8x and stopped at 5.8X.

I have the exact numbers photographed on my phone, I'll upload those later.

So, for half an hour of my time, I've concluded that in the real world (not the one that exists only behind your keyboard), the physics add up.

I'd also add that if I had actually been hypermiling I'd have beaten the spread by quite some margin. I might repeat next time I have a spare half hour.

For anyone interested in the BS, as you climb energy is stored at 100% efficiency. As you climb at BSFC, you're engine is 30% efficient (30% for a petrol as much as 40% for a diesel). As you descend the engine is basically 'off' or 100% efficient. Assuming you start and end at the same point, you've climbed 50% of the time and descended 50% of the time. The means you're net efficiency is 65% DFCO of course isn't really 100% efficient, but it's hard to quantify, at 90% it make little difference.

Compared to cruising on a flat which gives a 25% efficiency cruising on the flat. You can do quite a bit of braking in the decent and still come out ahead.

To those who failed science class thank you. The hills theory is one that I'd heard and based on my instinct seemed to be true, though I'd never seen it tested.

Still don't get it? Get in your car and try it.

UFI, the problem is that you don't actually have hills in Perth. Here in North Wales your driving style sadly wouldn't yield the same results.

Sweetsixteen said:

It is even as you say, oh great one!
Apparently, major car makers had a large input when this test spec was written up.
Speaks for itself really.
Happy driving.
Ciao.

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Yes the car makers had input in designing the NEDC.

Imagine trying to design a test that's 'fair' to all the different types of cars and engines in production. Part of the reason the test calls for gentle acceleration is so all cars can complete it

Imagine if Porsche had designed it, a 500 would have to be ragged just to complete the thing. My more powerful cars do much better at cycle beating than the 500. The 500 is probably close to BSFC on the cycle, which is why in real world driving it's near impossible to beat.

Another anomaly of the test is that the city portion is 4km long from a cold start, that's OK for a petrol engine, but a diesel will be lucky to have it's thermostat fully open within that distance. If the test had been designed by manufactures that sell primarily diesels, it would have been longer or from a hot start.

44sunsets said:

Not sure why UFI's methods would be controversial. Makes sense to me. Accelerate and change up quickly so you use the higher gears sooner.

My Dualogic has an annoying tendency to hold on to the lower gears too long, so I often shift up using the paddles.

UFI, are you on Fuelly? Would be really cool to see your progress as your TwinAir is run in properly

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It's as though I'm arguing that the earth is flat (which it turns out would be bad for fuel economy ).

I'm not on Fuelly, I'll PM you where I record my mileage.

I just drive UFI Italian style at the moment. I lost interest when my 2 ton van started doing as well in the city as the TA does in mostly highway driving. I'm going to do a test at some point of the two being driven side by side at the same pace on the same roads. My money is on the van getting the better MPG's. At about 3000km a year UFI won't be fully run in for a while yet sadly, but yes, I'll be going for MPG's then

306maxi said:

UFI, the problem is that you don't actually have hills in Perth. Here in North Wales your driving style sadly wouldn't yield the same results.

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Oh, I was using the wrong kind of hill?

Seriously, in a theoretical world the perfect hill would be one that you can climb at witchcraft (BSFC) and descend at magic (keeping at the speed limit without brakes). I think such a hill exists outside Charles Gardiner hospital, I'll test it in full hypermiler mode.

The worst hill would require ascent at WOT, followed by a nearly sheer cliff full of switchbacks.

But I think we can agree that there are enough hills in between these extremes where the net gain or loss is zero, or close to it.

My experiment represents a small scale test. I was surprised to get such consistent and repeatable numbers. For the record UFI sees a lot of driving in the hills of Perth and is one of the most economical TA's on here. When I get some time I'll scale up my testing on Greenmount, which is about the best I can do. 'Till then I'll continue to see hills as a friend.

PS Weren't you recently accused of using a hill for a test that wasn't steep enough?

306maxi said:

Yeah, the problem with hills is that if there's a bend on the other side and you have to brake and you lose that energy you put in.

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GPS can let you see over crests

UFI I have removed some of the padding for brevity..

UFI said:

I was a bit early for work today so I ran a test.

..there's a hill on either side. .......I did three figure of 8 loops crossing the carpark a total of six times, ...My commute had recorded a convenient 6.00....

Techniques ..were ..basic. Climb uphills at 100% load, coast in gear on the way down. Second run .., starting at 6.00, pulled into the parking spot after my figure of 8 and.. came in at 5.8X!

Third run in the same direction as the first. Started at 5.8x and stopped at 5.8X.

So, for half an hour of my time, I've concluded that in the real world (not the one that exists only behind your keyboard), the physics add up.

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So that suggests you improved your fuel consumption as compared to your commute on a totally different section of road that was driven in a different manner.

How about you do this instead:

Find a long flat piece of road. (Plenty of that in WA.) Then use your modified hyper-miler technique to "accelerate at 100% load to a bit below the speed limit, then lift off fully and" coast to a stop. Repeat this several times, until you have baseline consumption. Say you do it 6 times and and use 6 kms of road in the process.

Now find another straight 1km section of road with a hill in it. You pick the hill size. Climb the hill at 100% load and coast to the bottom. Repeat 6 times.

Two tests over 6km one with hills one without out. Compare Figures and report back.

I might then start to be convinced

Logger, you'd be more convinced if you did this experiment yourself, surely. Nothing better than personal experience.

logger said:

So that suggests you improved your fuel consumption as compared to your commute on a totally different section of road that was driven in a different manner.

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I still feel this is a valid result because the starting base line is irrelevant. I would have reset to zero, but this particular gauge let me zero everything except the 'short trip' parameter I was interested in. At any rate I still need a base line of some sort.

If my base line was 12.00 (vs 6) at the start for example then on the first lap my consumption would have still gone up on the first hill to 12.10 (vs 6.2), and still returned to 12.00 at the bottom.

Had the baseline been 3.00, I'd expect to have seen 3.4 at the top, but again a return to 3.00 would be expected at the bottom.

The fact that subsequent laps got better and better is probably due to me getting more and more used to the routes. The point is not that I improved compared to my commute, but that the extra fuel used in the climbs was payed back on the descents almost exactly.

I'll point out that these plug in gauges aren't 100%, and the slight discrepancy between each lap is within margin of error.

Find a long flat piece of road. (Plenty of that in WA.) Then use your modified hyper-miler technique to "accelerate at 100% load to a bit below the speed limit, then lift off fully and" coast to a stop. Repeat this several times, until you have baseline consumption. Say you do it 6 times and and use 6 kms of road in the process.

Now find another straight 1km section of road with a hill in it. You pick the hill size. Climb the hill at 100% load and coast to the bottom. Repeat 6 times.

Two tests over 6km one with hills one without out. Compare Figures and report back.

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I've got a longish trip coming up in a couple weeks I hope to put to use.

When you actually start looking for perfectly flat roads, you realise they're not than common (Perth is surrounded by hills so you have to drive about 400km to get to the desert roads you might have in mind).

What you describe is actually comparing hills to 'pulse and glide'.

Sweetsixteen said:

Logger, you'd be more convinced if you did this experiment yourself, surely. Nothing better than personal experience.

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True, however my mischievous side cannot resist the idea of convincing a card holding hyper-miler to waste the fuel to prove the point

As my regular readers will know, this is a subject quite close to my heart, so I've been following this thread with interest.

Half a million miles of real world experience basically would confirm what most of you have been posting - that hills mean worse economy and that single mindedly focusing on BSFC curves will rarely lead you to the best ecodriving style.

UFI is spot on in saying that ecodriving is basically an exercise in energy management, and the first thing I'd suggest to someone wanting to improve on their performance is to do a bit of serious pushbike riding.

The ultimate energy management machine is probably a glider - you are basically gambling your life on your ability to get it right every time you fly. For that reason, gliders generally have very effective airbrakes.

You then need to consider all the different ways in which energy can be taken out of the system and ruthlessly address each one; there are many more things which dissipate energy than just pressing the brake pedal.

The huge gaping hole in UFI's argument is that coasting in gear with your feet off the pedals is hugely wasteful in energy because of the significant pumping losses and mechanical drag of the windmilling engine; going downhill in gear with your foot off the gas isn't a zero energy solution because of engine braking effects.

The arguments might have some validity if you coasted downhill out of gear with the engine off, but that's hardly a safe or practical way of driving.

It is very, very difficult in practice to get back all of the potential energy you've stored climbing a hill; practical considerations make it all but impossible in nearly every situation.

Whichever way the theorists want to argue this one, my own long term results are in my sig and you are welcome to improve on them, if you can.

logger said:

True, however my mischievous side cannot resist the idea of convincing a card holding hyper-miler to waste the fuel to prove the point

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Stop making me laugh! It hurts.
Gotta agree with you - keep the fun going.

What's more/less efficient though? A windmilling engine or an engine out of gear and having to burn fuel to spin itself round?

306maxi said:

What's more/less efficient though? A windmilling engine or an engine out of gear and having to burn fuel to spin itself round?

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The latter.

It takes less energy to turn the engine at idle rpm that to turn it at cruising revs with the throttle plate shut. Now you have the challenge of finding an on-road situation where it's practical, and more importantly safe, to make use of that information. Hint: it serves no constructive purpose to arrive at the bottom of a hill with kinetic energy (=speed to normal folk)) which you can't safely use.

An engine out of gear and switched off uses less energy that both of the above, but the opportunity to make use of this safely occurs very rarely in real world driving.

I'm not giving away all my secrets or someone might beat my figures!

UFI said:

I still feel this is a valid result ..
The point is .. that the extra fuel used in the climbs was paid back on the descents almost exactly.

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Almost.

UFI said:

I've got a longish trip coming up in a couple weeks I hope to put to use.

When you actually start looking for perfectly flat roads, you realise they're not than common (Perth is surrounded by hills so you have to drive about 400km to get to the desert roads you might have in mind).

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Yep, Drove the Anne Beaddel, Connie Sue, Heather, Gun barrel, Gary Highways and Wapet tracks across WA a couple of months ago. Best we could do was about 20l/100km! But that wasn't in a Cinquecento. At the time it made me laugh when someone else around here declared Australian roads were better than those in UK! He has clearly never driven those highways. I did expect the WA deserts to be flatter than they were though.

UFI said:

What you describe is actually comparing hills to 'pulse and glide'.

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Yep, I only suggested it, because it would seemingly be the most fuel efficient way to cover the distance. Assuming the distance matched one pulse and glide. In the same manner as your climbing the hill at 100% load & then coasting down with next to zero fuel is the most efficient.