Improving fuel economy of bigger and smaller vehicles

[Justme]

No,I'm NOT stacking the deck with conditions. I'm asking simply, is it, in theory, possible to use less fuel utilising coating as a technique, or not? If not, how are the scenarios above explained?

Good point regarding switching the ignition off. Some of the hypermilers linked to above do this. Madness. But it obviously works.



Yup, conditions do exist where it's possible to provide a net benefit.



Tell that to the hypermilers.

Hypermilling is not about coasting down a hill.
Most google hypermiling sources say that clutch down coasting should not be done.
In this quote they say "coasting" but actually mean on over run.
2
Drive as if you don't have brakes — coast as much as possible.When you're driving plan a path that doesn't require braking followed by a sudden start. Careful coasting can reduce your gas usage so much that acceleration won't even cause a hiccup in your cruising mpg.

• On newer cars if the car is in gear and your foot is off the accelerator, the injectors shut off completely, creating essentially "free" mileage — your car's going but you're not using gas beyond a small amount for engine braking, or the engine's resistance to your costing.
• Don't coast by disengaging the clutch and/or putting the car in neutral. This will cause the engine to go into idle which uses up more gas than simply leaving the car in gear and letting it coast along with minimal engine input.[1]
• Source https://www.wikihow.com/Hypermile

 

[Justme]

Makes a huge difference if you are in another truck.

Bob

But looking at the big picture the vehicle in front then has a lower MPG is my understanding of slipstreaming.

 

[8ob]

But looking at the big picture the vehicle in front then has a lower MPG is my understanding of slipstreaming.

But the ten plus up his chuff are doing well out of it

Bob

 

[Farside]

Slipstream lorries on the motorway.

There are two ways of doing that.
1. Get right in behind them (dodgy as feck).
2. There's a secondary slipstream point about 100ft or so behind a container wagon where the air bounces off the road and rises up again, meaning you can sit in this secondary unturbulent bubble out of the worst of the weather.
Source: Me, doing 400 miles in the worst Easter of the late 20th Century, when I was caught out with summer gear and had to be back for work on the Monday.

 

[Gareth J]

Hypermilling is not about coasting down a hill.
Most google hypermiling sources say that clutch down coasting should not be done.
In this quote they say "coasting" but actually mean on over run.
2
Drive as if you don't have brakes — coast as much as possible.When you're driving plan a path that doesn't require braking followed by a sudden start. Careful coasting can reduce your gas usage so much that acceleration won't even cause a hiccup in your cruising mpg.

• On newer cars if the car is in gear and your foot is off the accelerator, the injectors shut off completely, creating essentially "free" mileage — your car's going but you're not using gas beyond a small amount for engine braking, or the engine's resistance to your costing.
• Don't coast by disengaging the clutch and/or putting the car in neutral. This will cause the engine to go into idle which uses up more gas than simply leaving the car in gear and letting it coast along with minimal engine input.[1]
• Source https://www.wikihow.com/Hypermile

So, what if you "drove like a granny"

Unless you were driving like a granny you have no speed to gain whilst going down hill.

Why did you need to put in that caveat?

If blanket coasting always cost more fuel than not, you wouldn't need such caveats.

I'm pretty sure we do agree that coasting *can* result in an increase in mpg but that to use it effectively isn't straightforward, definitely dangerous and even maybe illegal.

 

[Wightsparks]

On the OP's original question, if you can add a canvas cover from top of the cab to the top of the tailgate and down to the sides
a) it would look like the Cybertruck and
b) you would be a LOT more aerodynamic saving a decent amount of fuel.

 

[redlig]

Many years ago, I had a Saab 96. You could pull a lever and activate a one way clutch in the gearbox, which meant no engine braking. You could coast down hill, in gear with the engine idling and just hit the throttle when you wanted power. It was *claimed* that it was safer on ice. I was told later that it was to stop the original two stroke engines from seizing due to lack of lube on the overrun. I preferred having engine braking, but my dad had one previously a few years before and always drove in freewheel. I did fit an aftermarket CD ignition on mine and consistently got 39mpg. Considering I was in my early twenties and didn't hang about, and it was a heavy beast, I don't quite understand why cars don't do 100mpg with ease these days.

It could be something to do with having to haul all the junk that customers 'want' around . plus having to generate the electricity to power it . Add to that the weight of all the 'safety features ' ( crush zones/ airbags etc) also super comfy seats ,sound deadening and on and on . It all has to be accelerated and slowed. A well known race tuner said years ago " what isn't there doesn't have to be pulled up hill'.

 

[Memmeddu]

Sit on , and don't turn key,then close your eyes and drive with your imagination.

Now seriously run it at idle.
My car does 8km/litre if I push it (2500/4500 RPM)
While driving it at idle 1000RPM it will do 23km/litre

 

[Robbie260]

On the OP's original question, if you can add a canvas cover from top of the cab to the top of the tailgate and down to the sides
a) it would look like the Cybertruck and
b) you would be a LOT more aerodynamic saving a decent amount of fuel.

Have a canopy on the back so that dose help a bit.

 

[keithski122]

There are two ways of doing that.
1. Get right in behind them (dodgy as feck).
2. There's a secondary slipstream point about 100ft or so behind a container wagon where the air bounces off the road and rises up again, meaning you can sit in this secondary unturbulent bubble out of the worst of the weather.
Source: Me, doing 400 miles in the worst Easter of the late 20th Century, when I was caught out with summer gear and had to be back for work on the Monday.

Back in the nineties I used to do it the first way when travelling about on my scooter, flat out I could sit nicely right behind them until another truck overtook, zap in behind them, overtake the first and carry on my journey.

 

[bricol]

I once had the dubious privilege of being passenger of a guy who applied throttle up to 70+, let it coast in neutral down to 50-odd then repeat, ad nauseum, all the way along the M8.
Stupid and dangerous, in my opinion.

I had the same - a long time ago , in an Astravan - he also didn't want to wear out 4th gear too much, and really really wanted to preserve 5th for the end of the world . . . similar with lanes on the motorway, didn't want to wear the inside one out in-case lorries needed it, and the outside one might as been a toll road that he couldn't claim on expenses . . . my neck was knackered by the time we got to Ford's Basildon radiator plant from Bradford . . . I drove back!
Asked me why I used all the lanes, but only when overtaking . . . "because I've paid for 'em . . " . . .

Same bloke,when he left and contracted back, could set off to the same place, from closer to it, and claim for more miles than I did . . .

 

[bricol]

This is a common myth that often gets aired during discussions about using engine braking. It is patent nonsense as there is no additional, let alone excessive load on the drivetrain when on the overrun.

Once had a gearbox man tell me gearboxes were designed to transmit load from engine to prop rather better than the other way. The thrust loads from gear mesh can be considerable, and now going the opposite way can cause bearing failure, or even case failures over time.

Which hasn't stopped me for the last 30 odd year downshifting as I break and using engine braking to help.

 

[bricol]

Makes a huge difference if you are in another truck.

Bob

Back in the early 90's I used to occasionally drive Welcome Breaks refrigerated LWB Transit high foor - with the fridge up on the roof.

Foot to floor up the M1, I'd be slowly gaining on a lorry in-front . . . finally close enough to pull out to overtake . . . and the lorry would pull away as I slowed down from having to shove my own wind out of the way . . .

 

[PhillipM]

Once had a gearbox man tell me gearboxes were designed to transmit load from engine to prop rather better than the other way. The thrust loads from gear mesh can be considerable, and now going the opposite way can cause bearing failure, or even case failures over time.

Which hasn't stopped me for the last 30 odd year downshifting as I break and using engine braking to help.

Nah, the shock load when you lift off is way above what's normally transmitted coasting, never mind when you slam the anchors on in a low gear - it's one of the old wives tales that one tbfh.

 

[DAPPH]

My BIL used to drive all over the country delivering cars. One day he drove me down the M6 in my diesel Passat and annoyed the hell out of me because he pulsed the throttle, not losing any speed, but just on for a few seconds, off for a few, on for a few, etc. When I moaned about it, he said he did it to save fuel, and sure enough the trip had gone up from mid 50's for me to mid 60's for him!

That's how the reliant robins got massive miles from a measured gallon

I was taught this coasting in a whispering gear is illegal as you don't have full control of your car / bus /lorry truck etc. ...... especially in a 104 ton vehicle or a fully laden Landrover pulling a fully laden trailer . It matters not a jot if you are using a hand operated air brake on the trailer too or an over run brake .


It's highly dangerous as suddenly you have lost transmission which helps in braking when your foot is off the accelerator instead of heating up your brake pads , disc's, drums or shoes . Have none of you ever seen & observed road signs that indicate a steep decline and have the warning ," Engage low gear when descending hill "?
It actually applies on all inclines that you don't coast down it out of gear .

 

[DAPPH]

Once the car is demisted turn off the aircon.
Re tyre pressures, I think you should run them a bit high , they are only going to go down. In getting on for 50 years of driving I never heard anyone complain that their tyre pressures had gone up!

On the long runs from Calais to Spain , Southern France or Italy we did the recommended extra pressures for when the tyres warmed up & expanded .... there were numerous free air checking places along our route the further we drove south .. On very hot road surfaces IIRC they put the tyre pressures up a few more pounds , even higher when towing the shed .

 

[Edward Teach]

This one is getting some mileage,
Excuse the pun

 

[Morrisman]

Down side is that engines gearboxes & clutches cost a lot to replace when eventually needed compared to brakes that are cheap even if need more often.

Simply closing the throttle early enough doesn’t wear anything out.

I find rolling down long gradients behind cars, while they all have brake lights on, I have to give a whiff of throttle, even in top gear, or I am slowing down more than they are.

 

[8ob]

Its all a bit subjective, bottom line is someone that can read the road and that is mechanically sympathetic will get better mpg than a club footed brain dead moron. There are a few roads around here that get long tailbacks leading up to junctions, all the sensible ones back off and let their cars/trucks trickle along in first gear without having to start/stop, there are always half a dozen hooligans in the mix that want to drag start and anchor up at every car length space created upsetting what could be the most economical approach, and they never seem to tire of it A mate of mine runs a fleet of trucks, he can tell from the fuel used and service/maintenance costs who the numpties are.

Bob

 

[redlig]

Sit on , and don't turn key,then close your eyes and drive with your imagination.

Now seriously run it at idle.
My car does 8km/litre if I push it (2500/4500 RPM)
While driving it at idle 1000RPM it will do 23km/litre

Uses even less if you get out and push it .