Uphill/downhill Fuel Consumption

[Rabbers]

Living as I do in a hilly area, I constantly notice that my 300h's fuel consumption

increases quite substantially during stretches of uphill driving. While this is not in

itself unusual, I am nevertheless puzzled by the distances the car subsequently

requires in order to revert to the original rates of consumption. These distances,

which may be downhill or on the flat or, more usually, combinations thereof, are

in my experience at least two or three times longer than the uphill ones, but they

include so many variables in terms of gradients, curves, use of brakes, EV-mode

etc., etc. that it is impossible to make meaningful comparisons.

Does anyone know of a mathematical formula which enables a driver to estimate,

all other things being equal, how far he needs to travel downhill in order to regain

what he lost going uphill? And if any such formula exists, does it also apply the

other way around? Namely, how far uphill will you expect to have driven before

losing the saving obtained from the preceding downhill stretch?

All this may sound academic, and it probably is, but I am nagged by the thought

that better knowledge of the subject could point the way to improved driving

technique and economy in the types of area in question.

[Richard1200]

Wow, I do know that E=MC2 but that's it.

This is not meant to be a serious reply because you lost me half way through. You could find a job and a house in a valley or just drive and enjoy your car. Sorry to be no more help but this site needs to lighten up a bit.

[Rabbers]

Richard:

My sincere apologies for losing you halfway through my over-heavy post. I guess you must be one of the

few 300h owners who do not look at the consumption figures in front of you. I admit I once turned them off

for a whole day but the resulting loss of mental energy did not make me enjoy driving the car any better. I

promise to throw a few jokes into any future post.

[Richard1200]

Good reply.

I do have my consumption figures on but they are what they are. As they are virtually double what my IS250 was I am very happy.

Happy motoring to you.

[DJP]

All I know is I've halved my petrol bill, and the car is cracking fun to drive.

I achieved a grade 1 CSE in maths when God was a boy, so can't help with the formula stuff.

Sent from my Iphone using Lexus OC

[Shepherd]

Hi lucky IS300h owners :)

This post is a big IMHO

The way it works is that you loose energy going up as well as going down. This is due to friction, air resistance, engine heat etc. When you are going up hill you are fighting against gravity, while down hill gravity is helping you .In most cases the car is driven hard going uphill in higher revs, where engine efficiency is at its lowest. Thus energy losses are high. Going downhill you are still loosing energy, so not able to recover 100% of energy lost going up.

This is not a hard fact but I think in normal condition it would take twice or more of going downhill to normalize the mpg to compensate for the uphill struggle.

[ColinBarber]

When you go up hill you can see how poor the mpg is, maybe 20 mpg or less, and that will quickly bring down your mpg average for the tank of fuel.

At best, if you when you got to the top of the hill you turned around and rolled all the way back using no petrol your average going up/down the hill would be 40 mpg. That is probably still way lower than your tank average of 50+ and will take some time to recover that long running average consumption figure.

[RunningInPleasePass]

Some light reading on this subject!

http://www.roperld.com/science/hillydriving.pdf

[DJP]

Some light reading on this subject!

http://www.roperld.com/science/hillydriving.pdf

That should keep Rabbers happy!!

Sent from my Iphone using Lexus OC

[Richard1200]

Some light reading on this subject!

http://www.roperld.com/science/hillydriving.pdf

OMG, yawn, yawn. There has to be more to life than creating or reading a article like this. Someone really has got too much time on their hands.

[DJP]

One mans meat is another mans poison....

Sent from my Iphone using Lexus OC

[Joglesby]

Wow, just gone through the roper article......................Not to sure but I think it explains why consumption increases a lot quicker than decreases, so drops to 45ish on a long hill but takes ages to recover back to 50ish.

Nearly 6 weeks use now and find it jolly good. I suppose an average of 50 to 50.5 is ok.

[Rabbers]

RunningInPleasePass:

Thanks for providing the "hillydriving" link. As correctly imagined by DJP my delight upon its perusal knew no

bounds even if I would have preferred something a little less rich by way of breakfast reading. Nevertheless,

having fully digested the piece along with my cornflakes, I approached my 300h with a purposeful mien and

spring in my step and drove off in search of the nearest hill where I could test the accuracy of the equations

and, hopefully, further consolidate the almost mystical bond between man and machine. I regret to report

that my findings were inconclusive, and that, notwithstanding the yearnings of an eager public, I will never publish them.

Seriously, I was interested to see that someone somewhere (actually the former Head of Physics at Virginia

Tech) has devoted a heavy piece of thought to the subject. As for myself, it merely crossed my mind that

possible adjustments to everyday driving techniques (even for those of us who live in valleys but frequently

have to drive up and down the sides of them) could narrow the large disparities of fuel consumption in

stretches of hill driving and therefore maybe enable greedy people like me to squeeze an extra few km

out of the tank of what, in the case of the 300h, is already a very economic car.

Since starting this Topic, I have seen that it has been raised at least once before in this Forum quite recently, when I must have missed it: see Tips for Mountain Driving, started by Dochybrid on June 10, 2014.

[DJP]

Rabbers, you're going to have to think up something else to challenge the collective intellectual might of this forum :D .

[Richard1200]

On a serious note there are now far too many distractions from the actual art of driving. Using a hand held mobile is illegal while driving, at some time in the future I believe it will also be illegal to use and operate all these extra features which do distract your attention from driving. I am guilty of this my to the annoyance of my wife and I am a techno novice compared to some.

[Rabbers]

Richard1200:

We are finally in agreement about something. Yes, the amount and nature of the data the 300h constantly puts in front of you is a distraction from the art (in my own case the simple act) of driving. The consumption

data in their several variant forms always prompts me to respond with mental arithmetic of my own with an

obvious loss of concentration on more important things such as the actions of pedestrians and other drivers.

When I add to this the temptation to unnecessarily fiddle with the navi, audio and ventilation systems, I get

a feeling of nostalgia for the sardine-can technology of the Citroen 2cv which was the first car I owned many

decades ago. But on the other hand I suppose we have only ourselves to blame if we are the victims of an

excess of technology, and it would be hypocritical of me to say otherwise.