More miles per gallon

[dep]

Originally Posted by DavidY

But it doesn't say that coasting by declutching or selecting neutral is illegal, either...

no,
I was alluding to the absurdity that coasting is little different to other vehicle attributes that few if any road users would wish to be declared illegal.

[Astro]

Originally Posted by DavidY

The current online highway code says But my old paper version includes the sentence "Do not coast, whatever the driving conditions" in that section. This seems to have been taken out. Even in the paper version, the sentence wasn't written as a "You MUST Not" which is normally what they do when there's an actual law about it.

Perhaps it's allowed on a coast road.

[dep]

Originally Posted by Astro

Perhaps it's allowed on a coast road.

[Gadget]

Originally Posted by Astro

Perhaps it's allowed on a coast road.

no, no, no, much more dangerous - No dancing West Coast Swing while driving!

[SteveK]

Originally Posted by RedFox

In my experience the tyres are usually bolted on too tight for them to be removed by hand, so you may as well leave the jack and spanner at home too...

Originally Posted by Astro

That is so true because a machine puts them on.

But what you can do is get a piece of hollow scaffolding pipe (DTS should have some bits) - about 2 feet long. Put the handle of the jack inside it and press down on the pipe. This gives extra purchase.

May sure you oil the wheel nuts first in case it breaks them. Or spray that stuff on - WD-40.

The piping can also come in handy if you are attacked on a lonely road.

You don't want WD-40/oil on the wheel nuts - you want to use "anti-seize", although any decent grease will do just fine. WD-40 is far too light an oil to be suitable, and will have evaporated by the time you need to change the tyres. Anti-seize is available from any Halfords or similar place, but a thick waterproof grease will work just as fine.

My advice is that every time you buy a car, you individually remove every single nut one at a time, put plenty of anti-seize (or waterproof grease if you don't have anti-seize) on the bolt thread, and then tighten each nut.

The scaffold tube lever on the jack handle is a useful technique, but if you had put anti-seize on the nuts earlier, and checked the correct tightness of all your car nuts earlier, there won't be a need to use it.

Lubricated nuts work more effectively than ungreased nuts (insert innuendo as you feel fit) - it's prudent to check all these things one quiet weekend, as it will save you a lot of trouble when you get a puncture on a motorway on a cold wet windy night.

[dep]

Originally Posted by SteveK

a motorway on a cold wet windy (night).

do these exist in Ozzyland?

[SteveK]

Originally Posted by dep

do these exist in Ozzyland?

Not in Queensland It's getting really quite cold at night now it's autumn here - down to 15 degrees, and I'm finding it freezing

However I used to live in Inverness for quite a few years - so definitely understand the concept of "horizontal rain". Checking you can undo the wheelnuts before you have a puncture seems a sensible idea to me - you check oil/water/tyre pressures on a regular basis, so it's an easy thing to do once.

[Astro]

Originally Posted by SteveK

My advice is that every time you buy a car, you individually remove every single nut one at a time, put plenty of anti-seize (or waterproof grease if you don't have anti-seize) on the bolt thread, and then tighten each nut.

Lubricated nuts work more effectively than ungreased nuts (insert innuendo as you feel fit) - it's prudent to check all these things one quiet weekend,

...a dirty weekend? innuendo inserted.

as it will save you a lot of trouble when you get a puncture on a motorway on a cold wet windy night.

Not to mention the cost of calling the recovery service out.

Originally Posted by SteveK

Checking you can undo the wheelnuts before you have a puncture seems a sensible idea to me - you check oil/water/tyre pressures on a regular basis, so it's an easy thing to do once.

A stitch in time saves nine.

Another money saving tip - make sure your tyres are at the correct pressure.
Lack of air in the tyres will cause you to use more petrol.

[StokeBloke]

Here's a couple of extra ideas for you Mr David of The Scaffold.

1. Make sure your tyres are correctly inflated
2. You can buy tyres that are designed to maximise MPG - check next time your motor needs new boots
3. Smooth is best. Easy on acceleration, easy on the braking. Try to keep the car moving at all times if possible, even if it's just creeping forward.
4. Don't use the aircon. That aircon compressor sucks loads of energy from the engine.
5. Don't use your cruise control.
6. Don't rev the engine hard.

Jeremy Clarkson drove a diesel Audi from London to Edinburgh and back on one tank of juice!

[Gadget]

Originally Posted by StokeBloke

4. Don't use the aircon. That aircon compressor sucks loads of energy from the engine.

I'm fairly sure that it 'engages' another motor/pump from the fan belt - and it's the fan belt that the engine turns over - more load on the engine, it has to work harder to turn at the same speed, it uses more fuel. I think the same is true for the heater and blower - turn them off and having them at a 'neutral' heat is meant to save, but I think it's fairly negligible.

I performed a little experiment to see how coasting(foot on clutch) vs deceleration(foot off gas) works; Coasting reduces speed from 55 to 50mph in about 7 seconds. Deceleration reduces it in about 5 seconds. Flat road, straight line, no wind.
Coasting has the engine ticking over at about 9000rpm, that's 1050 powered revolutions of the engine in the 7 seconds. Deceleration over the same 7 seconds would have 18000rpm for 2 seconds at 55mph, assuming the 5 seconds has 0 powered revolutions that's 600 powered revolutions in the same time-frame.
Conclusion:Coasting is about 50% more efficient than maintaining a constant speed.
Deceleration is about 40% more efficient than coasting.

BUT you feel 'deceleration' driving as a constant acceleration/deceleration like being on a bad boat journey. You still feel 'coasting', but not as much. I wouldn't do either with passengers unless I wanted them to feel sick.

[dep]

Originally Posted by StokeBloke

Jeremy Clarkson drove a diesel Audi from London to Edinburgh and back on one tank of juice!

I know he's prone to exaggerate but that sounds impossible.
Surely, they claimed to use diesel.

[TurboTomato]

Originally Posted by Gadget

Coasting has the engine ticking over at about 9000rpm, that's 1050 powered revolutions of the engine in the 7 seconds. Deceleration over the same 7 seconds would have 18000rpm

I think you mean 900 and 1800rpm unless you have an F1 motor in your car. In which case

[TurboTomato]

Originally Posted by Gadget

Conclusion:Coasting is about 50% more efficient than maintaining a constant speed.
Deceleration is about 40% more efficient than coasting.

I'm not sure about that - it would only ever be more efficient in the case of travelling downhill. Or is that taken as a given?

[Gadget]

Originally Posted by TurboTomato

I think you mean 900 and 1800rpm unless you have an F1 motor in your car. In which case

I'm sure the revometer says x1000 in the bottom corner... ahhh but perhaps the numbers say 1,2,3 not 10,20,30...

Originally Posted by TurboTomato

I'm not sure about that - it would only ever be more efficient in the case of travelling downhill. Or is that taken as a given?

I was driving on the flat, all up-hill indicates is that it takes a shorter time to slow down... and down-hill would take longer. So if you decelerated/coasted down hills and maintained the same revs going up hills, then it should work out the same numbers (assuming of course that you start and end at the same height)

If you "decelerate" going down a hill and maintain a constant speed, then you have effectively used zero fuel over that distance... in this case, it's doubtful your foot would be on the gas anyway, so your fuel economy wouldn't change.

I'm not sure about the pseudo-physics behind it either, but that's from a different point of view: I'm no mechanic, but I thought that accelerator controls the amount of fuel going to the engine, so basically the depth of the pedal to the floor would be what changes your fuel economy - rpm is just a convenient way to measure it.

[TurboTomato]

My point was that coasting only works in terms of efficiency when going downhill - if you do it on the level then your speed will decrease to the point at which you need to accelerate again up to the speed you start coasting from, thus using more fuel. I'm sure that would use at least as much as travelling at a constant speed.

[dave the scaffolder]

Drive at the speed limit i am up to 450 miles so far and still have a quarter of a tank left. I am trying for 6 to 700 miles on 80 litres of diesel.

DTS Dave XXX XXX

[Gadget]

Originally Posted by TurboTomato

My point was that coasting only works in terms of efficiency when going downhill - if you do it on the level then your speed will decrease to the point at which you need to accelerate again up to the speed you start coasting from, thus using more fuel. I'm sure that would use at least as much as travelling at a constant speed.

I'm trying to say that it doesn't work as well going down hill, because you are already coasting/decelerating.

I'm sure that if you gunned the pedal to the floor until you were up to speed again it would offset the saving, but gentle acceleration is only a fraction above 'cruising' revs; while coasting is waaaay below cruising revs. Think on it this way: you have just travelled 10 miles using the same fuel you would have if sat waiting at the lights. We are only talking about a +-5mph deviation from cruising.

[dep]

Originally Posted by TurboTomato

My point was that coasting only works in terms of efficiency when going downhill - if you do it on the level then your speed will decrease to the point at which you need to accelerate again up to the speed you start coasting from, thus using more fuel. I'm sure that would use at least as much as travelling at a constant speed.

no.
It applies to all occasions when minimal throttle is required to maintain speed. see post 22.
It did not apply to carburetors which always flowed some fuel, although Ford developed a fuel cut-off late on.
But the high rev fuel cut-off in most fuel injection systems is very effective in totally stopping fuel flow and can give a significant fuel saving if you're careful in learning how to use it without interfering with other traffic.

A petrol engine is very inefficient at low throttle openings. Whereas a diesel engine has an open intake ALL THE TIME and varies the fuel flow to change the output power.
It is the engine pumping air against the almost closed throttle (throttle describes it well) that wastes petrol.
Get the petrol engine operating in the region of best economy alternating with zero consumption that returns good fuel economy figures. Best economy is usually around half to three quarters throttle opening at around, or just below, the rev range that produces maximum torque.

ps,
a good petrol engine that produces maximum torque @ 2800rpm will always be more economical than a good petrol engine that produces maximum torque @ 4500rpm.

[dave the scaffolder]

OK sport fans I am now up to 550 miles and still just below a quarter of a tank left.

DTS Dave XXX XXX

[Astro]

Originally Posted by Gadget

I performed a little experiment to see how coasting(foot on clutch) vs deceleration(foot off gas) works; Coasting reduces speed from 55 to 50mph in about 7 seconds. Deceleration reduces it in about 5 seconds. Flat road, straight line, no wind.
Coasting has the engine ticking over at about 9000rpm, that's 1050 powered revolutions of the engine in the 7 seconds. Deceleration over the same 7 seconds would have 18000rpm for 2 seconds at 55mph, assuming the 5 seconds has 0 powered revolutions that's 600 powered revolutions in the same time-frame.
Conclusion:Coasting is about 50% more efficient than maintaining a constant speed.
Deceleration is about 40% more efficient than coasting.

BUT you feel 'deceleration' driving as a constant acceleration/deceleration like being on a bad boat journey. You still feel 'coasting', but not as much. I wouldn't do either with passengers unless I wanted them to feel sick.

Oooh be careful Honey.

If you hit ice or some other driver/pedestrian acts like a fool and you have to break hard, you will be out of control.