Do you really want to lower motoring costs?

Submitted: Tuesday, May 27, 2008 at 12:52
ThreadID: 58053 Views:2971 Replies:8 FollowUps:6
This Thread has been Archived
After responding to a query on fuel savings in a recent post I offer
the following for your consumption...By driving at 90kph my fuel usage has decreased by 23%, as opposed to sitting on 110kph.
Car is Peugeot 405 2L auto. Previous...7.7L/ ...6.25L.
Or 13k to a L to 16k . Country driving, no air, tyres @ 35psi.
Calculated over 2 tanks of juice, trips ranging from 25k to 200k,
lightly loaded, 2 persons.
My thoughts....bloody bewdy, thats diesel car economy from ULP.
I now drive at 90kph max & after 1500 odd k am used to it, & funnily enough I find I'm not the only one doing it.
Case 2...dropped Jack towing C/t from 110 to 100 & dropped fuel
usage from 5.5k to a L to 7.3k to a L. That is 32.7%!!!!. 4 adults,
loaded for trip to Broome, no air, tyres @ 40 psi, V6 auto. I estimate I can get that up to 8k/L by dropping to 90kph.
Now, the other major motoring cost is depreciation........
These two cars are worth under $20k combined. Depreciated @
10% is $40 a week. A $80k rig equates to $160 a week. That
pays my weekly fuel A/c twice.
That is how I am controlling my motoring costs, run an economical
daily driver, save a cheap (but reliable) 4WD for the holiday thing, & above all....SLOW DOWN. Now, I know that wont suit everyone, & yes, I would love a 200 V8 diesel, but I can live with
my situation, & wont be curtailing my trips around Oz.
I dont like high fuel & motoring costs but they will never go down,
so control what you can & dont fret over things you cant change.
What's your answer? cheers...oldbaz.
Back Expand Un-Read 0 Moderator

Reply By: Shaker - Tuesday, May 27, 2008 at 14:32

Tuesday, May 27, 2008 at 14:32
Much the same .... but expect to get flamed!
AnswerID: 306110

Follow Up By: Member - DAZA (QLD) - Tuesday, May 27, 2008 at 15:09

Tuesday, May 27, 2008 at 15:09
Yeah and less stress, I drive to Brisbane from the Gold Coast each
day, leave a bit early, drive in the slow lane, on about 95ks an hour,
and watch the others go by, I carry a fair bit of equipment in the
Navara, and still get about 750 KS out of a tank of fuel.

FollowupID: 572129

Reply By: Member - Oldplodder (QLD) - Tuesday, May 27, 2008 at 15:00

Tuesday, May 27, 2008 at 15:00
Good post, agree completely.

And better for the environment all around, besides more money in the wallet.

By my calcs, making a car produces about 15 tonnes of CO2.
At 2.5kg/litre fuel, at 10l/100k, thats about the same as 60,000k of CO2 production burning fuel. So if you don't have to have a new car, keep the old one, even if it is 10% less fuel efficient. Every one still wins.

My old 74 beetle gets 8.4l/100k, and is gaining in value, the appreciation almost pays for the fuel! Thats on 5000k a year.
AnswerID: 306113

Reply By: Member - Footloose - Tuesday, May 27, 2008 at 15:10

Tuesday, May 27, 2008 at 15:10
Unless on a motorway my usual speed has always been around 90K. Often I annoy the heck out of other drivers, especially those pulling CT's and in a hurry. Mind you I do tend to pass them as they stop to get fuel.
Driving more slowly is better for the driver and passengers also, as you arrive more relaxed and having enjoyed the journey more.
AnswerID: 306114

Reply By: Member - RFLundgren (WA) - Tuesday, May 27, 2008 at 15:25

Tuesday, May 27, 2008 at 15:25
Have to agree with all as we do the same now. Just about everywhere we go to whether it be a trip somewhere or just going from home down to Freo for the day we sit on 90 - 95.

Saves a fortune in fuel, far more relaxing and if anyone gets frustrated, then they will just have to get over it. We do the right thing though and do pull over to let people pass if we have a couple of cars behind us.

The most frustrating and irritating thing for me is the idiots who persist in tailgating and then rev around you to get past. I then take immense joy and satisfaction when we pull up at the next set of lights and are in-line with the person who just burnt about 10 litres of petrol getting around us. When will people grow up and learn........



My Profile  My Blog  Send Message

AnswerID: 306117

Reply By: traveller2 - Tuesday, May 27, 2008 at 15:28

Tuesday, May 27, 2008 at 15:28
Just remember though that due to gearing and the point at which peak torque is developedsome vehicles may actually be more fuel efficient at higher speeds.
Experiment with what your own vehicle can do.
The other biggy is underinflated tyres. Most modern car radials are meant to operate in at least the 35 - 40lb range, most 4wd's will also benefit from running 40 - 45 without affecting tyre wear.
As an example try pushing your 4wd when tyres are at 35lb on a flat surface, then inflate them to 40 and notice that much less effort is requred to move the vehicle.
Aggressive tread patterns will also knock consumption around, MTR's cost approx 2 mpg when fitted to a cruiser.
Also increasing tyre diameter and width can also have a detrimental affect on fuel consumption.
AnswerID: 306119

Follow Up By: Member - DAZA (QLD) - Tuesday, May 27, 2008 at 15:58

Tuesday, May 27, 2008 at 15:58
I tried a little experiment, a couple of weeks or so back, I drove from
Brisbane to the Gold Coast when the fuel guage showed nearly empty, I sat on 95ks per hour, and the plan was to fill up when the fuel light come on, it came on as I was pulling into our driveway,
a week later I done the same thing,when the guage showed nearly
empty, I sat on 100 to 110ks per hour and the fuel light came on
about 15ks from home, I know the story about sucking up crap from
the bottom of the tank, but I wanted to know how far one could go
on a tank of fuel, if you were desperate, when travelling.

FollowupID: 572138

Follow Up By: stevesub - Tuesday, May 27, 2008 at 16:58

Tuesday, May 27, 2008 at 16:58
I drove a rental car fitted with a trip computer that gave a real time read out of the l/100km used and the most economical speed was in the highest gear somewhere between 50 and 60kph - nowhere near the ideal torque for the motor, just less wind and other resistance.

It is a myth that higher speeds are more economical in a car because you are driving at the peak of the torque curve as wind and other resistance is wrecking any savings made.

Now can someone tell me the most economical speed over a certain distance in my boat, 10mph off the plane at around 1500rpm or 15-20mph on the plane at 3000 to 3500rpm or even higher at 22 - 25mph at 3700rpm, the manufacturer's recommended cruising speed.??.

FollowupID: 572151

Follow Up By: Peter 2 - Tuesday, May 27, 2008 at 18:06

Tuesday, May 27, 2008 at 18:06
Well perhaps you might be able to explain why my Humvee uses less fuel travelling at 100 - 105kph than at 90 - 95.
The engine is obviously not spinning hard enough at the lower speed to be in its power/torque range.
Aerodynamics don't come into it as there isn't any!! It is shaped like a brick with a vertical windscreen.
I thought I was imagining it at first but I've repeatedly got better economy at the higher speed on the same 200km trip, regardless of direction, wind or weather. Sometimes the difference is only 1l/100k other times up to 3 or 4 l/100k.
And to top it off it is easier to drive at the higher speed as the torque converter isn't locking and unlocking repeatedly.
As a matter of interest it usually gets 15.5 - 16.5 litres per 100k at cruising speed, not bad for something that weighs around 3 tonne, 6.2 litre V8 diesel, auto and has the a aerodynamics of a brick shi*house.
FollowupID: 572160

Follow Up By: stevesub - Tuesday, May 27, 2008 at 21:55

Tuesday, May 27, 2008 at 21:55
My experiences that I have mentioned above are the facts that I have observed with our own vehicles and rental cars. I also know that our Troopy is considerably more economical at 90 kph than 100kph. I did a trip from MLB to BNE a couple of years ago, one tank at 90kph, one tank at 100kph with cruise control doing its job. I cannot remember the exact difference but it was in the order of 2l/100km better at the lower speed.

Like the Hummer, the Troopy is nearly 3 ton with the aerodynamics of 2 bricks including a flat windscreen but less frontal area than a Hummer.

As for your Hummer, well good on you, but I think that you will find that most vehicles are more economical at lower speeds. You may have answered your own question with the torque converter not always being locked at the lower speeds. Our Troopy and the rental car where both manuals in 5th gear on mainly flat ground so no losses with an unlocked torque converter.

The general consensus with this thread seems to be that if you slow down the more economical most peoples vehicles are with a definite improvement in fuel used over a certain distance at 90kph when compared with higher speeds.

FollowupID: 572211

Follow Up By: ExplorOz Team - Kerry W (QLD) - Wednesday, May 28, 2008 at 01:24

Wednesday, May 28, 2008 at 01:24
Peter and Traveller
I was not going to post my observations, as most people just politely smile and nod when I tell them that my petrol RB30 Patrol gets far better fuel consumption when the engine is revving at or over 3000 rpm.
Which is well over 100 kph.

I first noticed this 3 years ago after fitting extractors and doing all the necessary mods I have described in other posts about improving the performance of these engines (including a 40 sq inch air ram on the snorke and 40 psi in the tyres) (time to put all that info in a blog I think)

My wife (the one on the dune) took the vehicle to North Qld to see her family and spent considerably less money on fuel over the 2200klm trip than when I drove. She informed me, that She sat on between 105 and 110 all the way ( She has a Toyota Celica and drives the Patrol the same way) . I have done the same trip many times at 100kph and at night sitting on 90-100 and had 2 lit /100km worse consumption -consistently. It is an easy run to do economy figures for as each way we stop for fuel once in Rockhampton and top up at our destination so I can do the same sections at different speeds day night ULP and PULP Summer winter hence some variations in figures
Figures 90-100kph - 17-18 lit/100k never changes since bought the vehicle
105-110 15-17lit/100k
110-115 17-20lit/100
Over 120 the fuel gauge just dropped too fast to bother going there
These figures have been consistent for the last 3 years.
As traveller suggests I think in such a heavy vehicle (which is shocking on fuel at the best of times) when the engine hits its most efficient torque/power band then the engine obviously uses less fuel. Overall it sounds and feels best at this RPM - Cant explain the wind resistance factor but Im not imagining these figures.

(Oh and I was given a sample of Fuel tabs to try last year I was very scientific about trialling them - didnt find any difference in fuel consumption figures at all - Just in case anybody is wondering about them.)
Thought this may shed some more light on the comments posted above.


Kerry W
Road Conditions Coordinator
Kerry W (Qld)
Security is mostly a superstition. It doesnt exist in nature. Life is either a daring adventure or nothing.
-Helen Keller

Lifetime Member
My Profile  My Blog  My Position  Send Message

FollowupID: 572235

Reply By: Member - Phillip S (WA) - Tuesday, May 27, 2008 at 21:05

Tuesday, May 27, 2008 at 21:05
I have got to agree.....I try to take my time, drive at 90 to 95 kph and use the gears more and I find this sought of driving very restful and enjoyable indeed. With the turbo six I get about 16.5 litres per 100 kilometers.
AnswerID: 306193

Reply By: Member - Richard K (NSW) - Tuesday, May 27, 2008 at 21:41

Tuesday, May 27, 2008 at 21:41
All good tips. I am just now starting to worry that a trip at ANY speed will soon be unaffordable for someone who lives from paypacket to paypacket (a la moi!). Already I am thinking that my 4wding days are over unless I either make more money or fuel prices come down - both of which I think are unlikely to happen! If/when diesel hits $2 per litre, I think the 4wd might have to go and replace it with another cheapie like our 2nd car (would love to flick the 2nd car and just have the Prado but with wife and I both working shiftwork and 3 kids to take to different schools/daycares, that aint gonna happen either) least I will save heaps on all the mods that I won't have to do (diff-locks, muddies etc)

Sorry to be all doom and gloom, but something has to change and unfortunately it looks like the lifestyle!

AnswerID: 306201

Reply By: Eric Experience - Tuesday, May 27, 2008 at 21:58

Tuesday, May 27, 2008 at 21:58
The other consideration is weight, remember Bourke and Wills, they started of with 60 tons and starved, Howitt went to rescue them,he took a rifle and a box of matches, he lived. Eric.
AnswerID: 306208

Sponsored Links