Close car windows to reduce drag.

If not needed, use a/c just occasionally to keep it working.

John

  Quote  

on a level road fuel consumption drops drastically no matter what the speed is as there is very little load on the engine (only overcoming rolling resistance).

Below 70 to 80 km/h that is close enough but wind resistance increases with the square of the speed. Above about to 80 km/h it becomes the main factor and fuel consumption starts rising again.
My car shows instantaneous l/100km and by 120km/h it is climbing steeply.

Here is an alternative, if you want to get away with the fuel cost, and at the same time improve your fitness.


   /Peter63

Once I was driving north from Sydney and the usual 110 km/h limit was cut  to 80 km/h for roadworks,  in sixth gear it was ticking along at an average 3.7 - 3.8 l/100k ..
very nice    ..
the problem is though,  that is below 2000 revs/min and so the DPF clogs up.

Sydney is not great for petrol/diesels, most traffic is congested and there are a lot of traffic lights as suburbia gets more crowded. The low speed and low speed limits mean low gears are usually needed to keep engines from stalling and that means more fuel burn. As well there are often 40 km/h "school zones" [even on major roads like the Pacific Highway] in morning and afternoon time
slots. So the DPF's (soot filters) don't get a chance to burn clean.

A PHEV turbo-diesel hybrid would be nice and about as efficient as possible ...
but way too expensive !!

I don't think there are enough charging stations yet for mainstream commuting EV's.

One "gotcha" is the vehicle manufacturers have to comply with "fleet average"
fuel consumption for their products and so have set the use of very low friction oils
with a 0w20 temperature rating instead of the original 5w30...if I understand it correctly, the thinner oil is not as protective and can lead to engine problems and faster wear - GM USA was burnt and they have now issued a voluntary recall on 6 litre V8's and will replace the entire engine if it is found to be damaged. That would be expensive .

People laughed at the Sinclair C5 unfairly IMHO. It was a work of genius!  :)
It had its problems, true, but as the basis for further development it was good. Imagine one with a modern digital motor, lithium battery and much improved power management.

  Mixtel90 said  

Imagine one with a modern digital motor, lithium battery and much improved power management.

Fit the motor and batteries from an e-bike and you’ve got an upgrade, or do a conversion like this one
Unfortunately, it’s very difficult to get such modifications approved for road use in Germany
Edited 2026-04-04 19:23 by Martin H.

  Mixtel90 said  

It would depend on how the engine is set up. They can tune almost any speed for best efficiency. I think it was traditionally set at about 40mph (64km/h) here in the UK.

I suspect approximately none are set for 20mph & under.

At 20 roads are (obviously) more congested and I gather emissions are worse as well as worse MPG (miles per gallon, i.e. fuel efficiency).

Anyone for a hybrid so it can run the engine efficiently to provide electricity and then use that for the wheels, with a battery as a kind of buffer?

Obviously avoid all brick-shaped cars if wanting fuel efficiency (or to kill fewer kids).

John

  Mixtel90 said  

People laughed at the Sinclair C5 unfairly IMHO.

They were very small & low and very hard to see.  Something a bit bigger would have been wise.

Plus, with at least a few more creature comforts.

John

YES! That's the C5 I want!  :D
Well, as close to what you can get in that size body shell anyway. Very nice job.

On the opposite side of the scale, my neighbour stopped his car this afternoon to show me what he has just bought; a Rolls-Royce Spectre.  He chose a massive add-on package of extras leading to an on-the-road price of over UK£600,000!  It is a massive car with 650HP available under your right foot.  Range is a rather limiting 250 miles, but, as he said, if you need to go further then just take your helicopter!

Ah, but he can't fit two of them in the back of a Transit. :)

G'day,

  Quote  

Obviously avoid all brick-shaped cars if wanting fuel efficiency

Hmmm, so this is probably not the way to go...


For a little perspective, 18L/100km driven carefully, 22L/100km+ if pushed... I really feel for truck owner drivers at the moment.
With a vehicle this un-aerodynamic the difference from 80km/h to 100km/h is more like 25-30%, she will do 125km/h but I don't even want to crunch the numbers  

A "difference of opinion" with my employer last year caused a "Change of employment" (IE I had a barny with the boss and got the arse), this also meant the loss of company car and free fuel. Of course, this happens half way through the 600000km long term rebuild of my trusty defender 110, she uses 10-11L/100km, not bad considering. So the 6x6 (normally the prospecting rig) is my current daily driver, just lucky to be working from home and only go out about once a fortnight  

I guess the idea is to find enough gold to cover the fuel cost. This will also run on Diesel / Kero / Jet Fuel / Canola / Vegetable oil without damage. No electronics (or even battery) required to make it go, always a silver lining  

Regards,
Lyle.
Edited 2026-04-05 14:31 by mozzie

  Quote  

I really feel for truck owner drivers at the moment

From Tanami Transport site:-

  Quote  

What horsepower are the trucks?
600 - 620 HP

How many tyres are on a road train?
There are 80 tyres on the ground and 8 spares carried by each unit.

How much fuel does a road train use?
The average is 1 kilometre to 1 litre of diesel. A road train can carry 2,000 litres of diesel when fully fuelled.

The pedal cars may be eco friendly but they won't pass safety laws soon.
Most drivers will have seen bad accidents in traffic.
Personally I want as much steel armour as possible when commuting. As a student in a car I bought for $300 and repaired to "roadworthy" status (hah) -you know the type, with mismatched doors etc- and  drove to uni in peak hour every day in the Melb winter  and traffic (sleet, 11 deg C, greasy roads, fogged windows, peak hour aggression ). I distinctly remember observing a truck wheel in the next lane taller than my car ceiling ! Ugh.

(added)
Also there was the expensive two-seater sports convertible, owner looking quite smug,
ahead at the traffic lights. A cattle truck pulls up next lane... The lights are still red... and a tail goes up, and the two occupants get a uh, sprayed gift of free fertiliser -  and they are strapped in with seat belts.  Priceless    
Edited 2026-04-07 03:33 by zeitfest

Nah... They'll pass easily when it's too expensive to run any other cars and trucks are limited to 15mph to save fuel. Pedestrian heaven.  ;)

There are reports that ethanol can easily be converted to diesel
but at about $6 / gallon  (US) which now sounds feasible  

  zeitfest said  

There are reports that ethanol can easily be converted to diesel
but at about $6 / gallon  (US) which now sounds feasible

In the U.S., corn grown for ethanol as a gasoline additive (10%-15%->20%) takes up 30 million acres of farmland. Whether energy-out for ethanol is greater than energy-in is in dispute.

Wind farms (which still allow agriculture on about 90% of the land) and solar farms would provide 60 to 100 times as much energy per acre for rolling wheels on a highway (and, of course, for all the other things electricity is good for).

There are combined solar and agriculture farms being trialled here..
makes sense as the daylight in much of Aus is such that even diffuse light is enough,
in fact some fruit and grains are sun damaged.  It would be good to see canola being grown for biodiesel under the PV's - bit hard to harvest I guess.