General 500 mpg

[Mick F]

yep, but surely she coasts down the other side, therefore only driving 50% of the way.

Absolute fallacy.

Ride a bike on the flat.
Ride a bike up and down hills.
Do you get back the energy expended going up when you go down?

Not at all.

Hilly country is harder work than flat country.

With an internal combustion engine, the engine turns over and powers the wheels. The car weighs 1000kg maybe and takes a great deal of energy and fuel to get it up. Coming down, gravity pulls the car of course so very little fuel is used. Trouble is, this doesn't cancel each other out. Pity really.

Drive your car on the flat for ten miles constant speed. Note the fuel consumption.
Drive your car uphill for a mile, downhill for a mile and do this five times same speed total distance ten miles. Note the fuel consumption.

Tell me now that the two consumption figures are the same.

Try it.
Mick.

 

[yostumpy]

Absolute fallacy.

Ride a bike on the flat.
Ride a bike up and down hills.
Do you get back the energy expended going up when you go down?

Not at all.

Hilly country is harder work than flat country.

With an internal combustion engine, the engine turns over and powers the wheels. The car weighs 1000kg maybe and takes a great deal of energy and fuel to get it up. Coming down, gravity pulls the car of course so very little fuel is used. Trouble is, this doesn't cancel each other out. Pity really.

Drive your car on the flat for ten miles constant speed. Note the fuel consumption.
Drive your car uphill for a mile, downhill for a mile and do this five times same speed total distance ten miles. Note the fuel consumption.

Tell me now that the two consumption figures are the same.

Try it.
Mick.

Ah but! 10 miles flat is 10 miles driving.
but 5x 1mile uphills is 5 miles plus 5 miles down hill . coasting on tickover is .....0 miles= 5 miles driving, (plus a bit for the extra effort of going uphill.)

Mick , you are a cyclist, if you ride a fully laden touring bike up the cheddar gorge, then decide to come down again, would you pedal down in top gear? no you would coast. I tend to drive as if I am a fully laden cyclist.I have a vw camper '76 2000cc. Now these aren't renowned for their economy, 22mpg on a run is considered good, but mine avg about 28.5mpg on fuelly, but have had 34mpg going to a festival a couple of years ago, fully loaded, uphill and down dale, using the above method.

Oh and i would rather do a hilly 200k Audax than one in the Fens.

 

[Mick F]

I have ridden up Cheddar Gorge, and also come down.
That isn't a valid test.

Go for a ride on the flat. Go as far as you want, ride all day. Maybe living in the South Midlands for instance. Maybe ride from John O'Groats to Land's End instead?

Which portion of a ride is harder work?
Is cycling from Carlisle to Bristol the same as riding from Bristol to LE?

Same as driving.
Go from Bristol M5, through Brum M5/M6 and keep going to Manchester at a steady 60mph.
Go from Bristol, down the M5 and A30 to Penzance at a steady 60mph.

Measure your fuel consumptions and tell me I'm wrong.

It would be wonderful to get back the fuel expended from going up when you go down, but mechanics don't work like that. They may do in theory ...... and I agree with you in that ...... but in the real world it doesn't.

Regards,
Mick.

 

[yostumpy]

http://ecomodder.com/

Fascinating forum for those with a mind to eek out that wee bit extra. Check out the 100+ tips for hypermiling. They DO work, but you have to try them yourself. also read some of the forum stuff. It acually becomes a challege, a sort of game, then you start to laugh a folks accerating past you approaching a roundabout, only to stop, but because you have slowed and anticipated, you have now just slipped on thro, whilst he is still finding first gear. Makes me a happy bunny every time.

 

[Mick F]

Yes.
Funny as heck watching people hurtling up to junctions and braking hard.

Going back to cycling, I'm no stranger to long distances. My last John O'Groats to Land's End trip was on a Raleigh Chopper towing a fully loaded trailer. Honest I did.
http://jogleonachopper.blogspot.com

Riding like that, really gives you the knowledge to coast when you can, pick out where and when you want to stop, and not brake very much. Braking wastes energy, not in the braking, but you've wasted energy going so fast that you need to brake at all. Coast to a stop as much as you can.

Coast down hills, freewheel as much as possible, take your time. It's all good stuff for economy.

Cheers,
Mick

 

[UFI]

Absolute fallacy.

Drive your car uphill for a mile, downhill for a mile and do this five times same speed total distance ten miles. Note the fuel consumption.

Tell me now that the two consumption figures are the same.

Try it.

I did this about six months ago and reported my results. As you might recall, each time I got to the base of the hill, fuel consumption returned to my baseline (if anything the trend was slightly better than baseline each time).

ICE engines are more efficient when ascending (moderate) grades and ICE engines are more efficient descending moderate grades, then they are simply running on flat ground. Hybrids use this principle to try and keep the ICE at closer to peak efficiency, than an average driver. It's also how I get 40mpg out of a van rated 31 (with better to come).

 

[jrkitching]

I did this about six months ago and reported my results. As you might recall, each time I got to the base of the hill, fuel consumption returned to my baseline (if anything the trend was slightly better than baseline each time).

ICE engines are more efficient when ascending (moderate) grades and ICE engines are more efficient descending moderate grades, then they are simply running on flat ground. Hybrids use this principle to try and keep the ICE at closer to peak efficiency, than an average driver. It's also how I get 40mpg out of a van rated 31 (with better to come).

Remember also that the shortest distance between two points in 3-dimensional space isn't up & down a hill. Even if you manage to get a slightly better mpg figure (which I suspect needs very much the right kind of gradient and a clear road), you'll likely use more fuel than if the hill wasn't there, because you'll have covered a greater distance in going up & down again.

And if you have to use any kind of braking (even engine braking) coming down the other side, I doubt very much you'll break even on the deal.

Trying to descend Cornish hills without braking would likely cost you far more in bodywork repairs than you'd ever save in fuel.

 

[Mick F]

Take the argument to extreme.

Imagine two identical right-angle triangles placed back to back so they form a wide isosceles triangle. Maybe use the standard 3-4-5 triangles.

These two triangles form a theoretical hill. Bottom of hill on the left is where you start - Point A. Bottom of hill on the right is where you finish - Point B. Top of the hill is - Apex. Hills are formed from the hypotenuse of each triangle.

Therefore, from Point A to Point B you have to drive (say) 10miles via Apex.
If you drove on the flat, it would be only 8miles A to B.

Now, going up the steep hill you do (say) 20mpg to Apex, but use no fuel at all going down the other side. Therefore you average 40mpg for the whole journey of 10miles.

On the other hand, if you drove the 8miles on the flat, you could very easily have averaged 50mpg.

This argument only works if the uphill is steep. Shallow hills I would agree don't affect fuel consumption overall because fuel consumption wouldn't suffer sufficiently going up.

As I said before, we live an a long 25% hill. Going up it costs fuel that you don't effectively get back when you come back down.

Cheers,
Mick.

 

[UFI]

Remember also that the shortest distance between two points in 3-dimensional space isn't up & down a hill. Even if you manage to get a slightly better mpg figure (which I suspect needs very much the right kind of gradient and a clear road), you'll likely use more fuel than if the hill wasn't there, because you'll have covered a greater distance in going up & down again.

Very true, but people who drive on hills seldom complain about having to drive the extra distance. Same goes for corners, taking the inside lane is shorter, while taking the outside lane causes less scrub and therefore higher MPG. I both cases there's going to be a cross over point where the improved MPG is cancelled out by the extra distance traveled. Bare in mind that if you want drive around a hill, that could mean extra distance too

And if you have to use any kind of braking (even engine braking) coming down the other side, I doubt very much you'll break even on the deal.

I did my test runs using engine and friction braking. My chosen route had speed humps on both the ascent and decent, stop signs at the top and bottom of the hills, round abouts etc. It was far from an ideal route. Remember that your ICE peaks at 30% efficiency climbing a hill, while being in DFCO is essentially 100% efficient (at least in terms of fuel use). Running steady state on flat ground likely means an overall efficiency for the ICE of 20%.

So using fairly normal techniques, climbing at 100% load (but closed loop still), and using DFCO and friction brakes on the decents on a less than perfect route, I still broke even. This also means that in perfect situations, I can do a fair bit better on a hill than I can on the flat. UFI's 100mpg run was deliberately done on (unfamiliar) hills, if I do the same run again I can probably top that. My 60mpg tank was also done with a lot of hills driving, in fact UFI spends a lot of time on hills, including some very steep inclines that would push him much faster than his engine could on the flat.

I have one perfect hill nearby that's a ~25% climb of about 300m (distance not height) followed by a long grade that tapers to flat. I use about 12l/100km to climb it, and then get a 1.5km coast free to the next traffic light (the start and finish elevation is basically the same). That works out to 2.4l/100km average for the 1.8km stretch, in a car rated 9.7 city (to date a best city tank of 6.3). Even if I factor in the extra distancethe of vertical elevation adds, it's certainly not enough to cancel out the gains. At the same speed, this car uses around 5.0 on the flat.

I like hills

 

[Mick F]

I have one perfect hill nearby that's a ~25% climb of about 300m (distance not height) followed by a long grade that tapers to flat. I use about 12l/100km to climb it, and then get a 1.5km coast free to the next traffic light (the start and finish elevation is basically the same). That works out to 2.4l/100km average for the 1.8km stretch, in a car rated 9.7 city (to date a best city tank of 6.3). Even if I factor in the extra distancethe of vertical elevation adds, it's certainly not enough to cancel out the gains. At the same speed, this car uses around 5.0 on the flat.

I like hills

Just done a trial on our hill.
I reset the trip meter at the bottom, and set off up.
Average speed was 8.5mph, average fuel consumption 8.3mpgUK. (34L/100Km)
The hill is 0.35 miles long and at 25%.
I was in first gear for some of the hill, and then second further up.
You can't go faster because it's a very narrow road without any decent visibility.

Your 12L/100Km at 25% uphill comes out as 23.5mpgUK. What was your average speed?

Thanks,
Mick.

 

[Sweetsixteen]

What's this unmeasured 'extra distance' with hills over flat roads?
Guess I must be extra thick - Not sure I understand this reasoning. It seems to suggest that hills are somehow ignored by the odometer.

 

[Most Easterly Pandas]

What's this unmeasured 'extra distance' with hills over flat roads?
Guess I must be extra thick - Not sure I understand this reasoning. It seems to suggest that hills are somehow ignored by the odometer.

Think of a long flat road as a piece of string thats got point A at one end and point B at the other. Lay it on a flat table and its 1 meter long.

Hold finger on point A, lift the middle by 20 CM, and point B will move closer to point A.

So get to the original point B position you'll need to lengthen your string - road lengths work exactly the same with hills etc. So distance traveled can potentially be greater than the distance as the crow flys, when it comes to hills. Hope this makes sense?

 

[Sweetsixteen]

Yep, I see that, but the odometer measures actual distance travelled whether the ground is flat or hilly. There are no 'lost miles' on the odometer, so it's a reliable guide from which to calculate fuel consumption ( allowing for any built-in errors on the odometer itself).

Apologies if I'm missing the point here - it looks as if some are saying that the odometer somehow doesn't measure hills, only flat land?

 

[UFI]

Your 12L/100Km at 25% uphill comes out as 23.5mpgUK. What was your average speed?

Had a big reply all typed up but lost it. Thumbs up for getting some data relevant to your situation. It sounds like low speed is what's costing you rather than the hill per se.

80% load on my 1.6 Renault corresponds to 12l/100km at 60km/h. If engine load and speed are the same it doesn't matter if I'm climbing a gradient, towing a trailer or even towing a trailer up that grade, if load speed and constant instantaneous MPG is the same. The only thing that changes in this case is the rate of acceleration, the longer time spent accelerating (getting poor MPG) is where the MPG hit comes from.

 

[Mick F]

. It sounds like low speed is what's costing you rather than the hill per se.

That is exactly my point all along.

Hills cost fuel and that fuel isn't recovered going back down. Yes, it can be if you have a good speed and momentum, but in the real world round here, you rarely get any momentum to help.

We spend many of our journeys in a low gear going up, and holding back on the brakes coming down. This is in the cars ..........and when I ride a bike!

The weather is clearing now, so I'm shortly off on my bike. The sun is coming out, so I'm off!

Regards,
Mick.

 

[yostumpy]

on downhills not restricted by brakes, there is a knack, when cresting a hill , say in 4th gear, and there is a long downhill ahead, say on A303 type thing, you then floor the pedal in 4 th for about 3 secs, then same in fifth, so the engine is under max load, to give you some umph!then knock it out of gear, then with the added momentum you coast a lot further, at a faster speed. Then coming to next hill, slip it back into gear whilst still on the downward, and floor it, to woosh you up, then ease off as you go up and make the engine work with less fuel.Its totally second nature to me now, this hypermiling lark, I drive with the thought that I'm in a post apocalyptic 'mad max' world, where every drop of fuel is precious, you cant hang about, and to stop is BAD NEWS BEARS.
Cant wait to get the TA

 

[Most Easterly Pandas]

on downhills not restricted by brakes, there is a knack, when cresting a hill , say in 4th gear, and there is a long downhill ahead, say on A303 type thing, you then floor the pedal in 4 th for about 3 secs, then same in fifth, so the engine is under max load, to give you some umph!then knock it out of gear, then with the added momentum you coast a lot further, at a faster speed.

No no no, leave it in gear while coasting down hill and you'll use no fuel during this period, putting it into neutral will use more fuel as the engine will be idling away, and will leave you with less control which can be dangerous!

 

[yostumpy]

use slightly more fuel yes, say 60-120 secs on tickover, but the distance covered is far greater out of gear, without the engine braking.quite often , out of gear, the vehicle will actually pick up speed, as opposed to being held back.

 

[yostumpy]

perhaps we should have a forum back- back Lands end / John a wotsismame, an Eco road trip.

 

[yostumpy]

https://www.google.co.uk/url?sa=t&r...gIHADQ&usg=AFQjCNEaXFYCaAgGJBVINIE1iJ4pOlm0jQ