Driving Economically.

Dave_C_2

In reply to me saying:

The OP missed several important points as detailed at the start of this expert advice.

alastairq wrote: »

it would be helpful if the points missed were in fact pointed out?
Then we could have a compendium of advice?
[feel free to challenge the AA and its assertions, however. In the end, they, too, often only supply opinion]

Quoting from the AA page linked:

Maintenance

• Servicing: get the car serviced regularly (according to the manufacturer's schedule) to maintain engine efficiency
• Engine oil: make sure you use the right specification of engine oil (check the handbook)
• Tyres: check tyre pressures regularly and before long journeys; under-inflated tyres create more rolling resistance and so use more fuel (check the handbook and increase pressures for heavier loads as recommended)

Before you go

• Lose weight: extra weight means extra fuel so if there's anything in the boot you don't need on the journey take it out
• Streamline: roof-racks and boxes add wind resistance and so increase fuel consumption. If you don't need it take it off – if you do, pack carefully to reduce drag
• Leave promptly: don't start the engine until you're ready to go as idling wastes fuel and the engine warms up more quickly when you're moving; in the winter, scrape ice rather than leave the car idling to warm up
• Don't get lost: plan unfamiliar journeys to reduce the risk of getting lost and check the traffic news before you leave
• Combine short trips: cold starts use more fuel so it pays to combine errands such as buying the paper, dropping off the recycling, or collecting the kids
• Consider alternatives: if it's a short journey (a couple of miles or so) could you walk or cycle rather than taking the car?

To be fair, the OP did say:

I'm not going to cover the tyre pressure/luggage/roof rack etc as they've all been done to death

But it's worth repeating.

I love the "don't get lost" one. Especially as you knew the route last time you were there three years ago, but they've redesigned the one-way road layout since then.
Maybe it should be updated and say "Update your Satnav".

HTH, Dave

alastairq

haha...not sure how 'getting lost' affects your fuel consumption?


I think the main factor today affecting fuel consumption utilises the advantages of ECUs and fuel injection...and the fact that, when 'off the gas' [over-run] all fuel is returned to the tank. [something that wasn't available to a carburettor- equipped car]....


To maximise this fact, I suggest 'coming off the gas' as early as possible in advance of junctions or speed limit changes....but keeping in top gear until the speed has fallen to the level desired.

this maximises the time and distance spent using no fuel......and by retaining top gear for as long as possible, this will reduce the 'engine braking' effect as the revs are low [ high engine revs give better engine braking effect]...

Once the reduced chosen speed is reached, simply select the appropriate gear for that speed...go straight to it...if the gear is right, there will be little or no 'take-up' from the engine.

[as an example, in my wee Felicia1.3, I will come off the gas at 60 in top, just allowing the speed to fall off naturally for a 30 limit...hopefully, if I get it right, 30 will be reached just before the speed limit signs...then I'l simply pop into 4th .......mainly because at 5th, the engine is only just above tickover at 30.....don't want to waste fuel, do I?]


Read the nature of the road in front....make use of downhill bits to come off the gas, but also use the 'sling-shot' effect in dips to get the car up the next rise, without any heavy gas pedal or gear changing....

Use uphill bits to slow the car instead of driving in and braking.....


If you know a downhill bit is coming, there's nowt wrong with gently speeding up to the limit, coming off the gas as you go over the crest.....maximise the 'over-run' for as long as possible?

But no 'coasting'.....when the engine is ticking-over, it uses fuel

Consider looking at how the car is steered?

Aim to be economical with the steering, utilise the whole width of the lane or carriageway available [without going over the centre line, I hasten to add...that's someone else's bit of road, not yours]...when dealing with bends or corners...even slight ones......the less those front wheels turn sideways, the less resistance to forward motion......there is much sense in the way racing drivers take bends......use the same sorts of line, but also use your eyes beforehand! [and your door mirrors]

Like motorcyclists, plan...or 'visualise' your intended path along a road....none of this 'weaving about' I see so many drivers doing....let the road weave about, not the car!

Helps with forward visibility too...the big secret when going through corners lies, IMHO,with the 'feeding-off' of the steering wheel....aiming to return to a similar road position that was adopted prior to the bend........a lot of drivers tend to stay tucked-in right through a bend.....'over-steering' I call it....makes the car less stable too..much better to feed off towards the outside again.

This sort of thing can be done at any speed.......so is not the preserve of the 'go-faster brigade'......[check out 'Roadcraft' for nice diagrams?]

Put an extra few psi in the tyres helps as well....keep the ratio front-to-rear the same, however, or the 'handling' will change.


my two pennyworth?

mikey72

alastairq wrote: »

haha...not sure how 'getting lost' affects your fuel consumption?


I think the main factor today affecting fuel consumption utilises the advantages of ECUs and fuel injection...and the fact that, when 'off the gas' [over-run] all fuel is returned to the tank. [something that wasn't available to a carburettor- equipped car]....


To maximise this fact, I suggest 'coming off the gas' as early as possible in advance of junctions or speed limit changes....but keeping in top gear until the speed has fallen to the level desired.

this maximises the time and distance spent using no fuel......and by retaining top gear for as long as possible, this will reduce the 'engine braking' effect as the revs are low [ high engine revs give better engine braking effect]...

Once the reduced chosen speed is reached, simply select the appropriate gear for that speed...go straight to it...if the gear is right, there will be little or no 'take-up' from the engine.

[as an example, in my wee Felicia1.3, I will come off the gas at 60 in top, just allowing the speed to fall off naturally for a 30 limit...hopefully, if I get it right, 30 will be reached just before the speed limit signs...then I'l simply pop into 4th .......mainly because at 5th, the engine is only just above tickover at 30.....don't want to waste fuel, do I?]


Read the nature of the road in front....make use of downhill bits to come off the gas, but also use the 'sling-shot' effect in dips to get the car up the next rise, without any heavy gas pedal or gear changing....

Use uphill bits to slow the car instead of driving in and braking.....


If you know a downhill bit is coming, there's nowt wrong with gently speeding up to the limit, coming off the gas as you go over the crest.....maximise the 'over-run' for as long as possible?

But no 'coasting'.....when the engine is ticking-over, it uses fuel

Consider looking at how the car is steered?

Aim to be economical with the steering, utilise the whole width of the lane or carriageway available [without going over the centre line, I hasten to add...that's someone else's bit of road, not yours]...when dealing with bends or corners...even slight ones......the less those front wheels turn sideways, the less resistance to forward motion......there is much sense in the way racing drivers take bends......use the same sorts of line, but also use your eyes beforehand! [and your door mirrors]

Like motorcyclists, plan...or 'visualise' your intended path along a road....none of this 'weaving about' I see so many drivers doing....let the road weave about, not the car!

Helps with forward visibility too...the big secret when going through corners lies, IMHO,with the 'feeding-off' of the steering wheel....aiming to return to a similar road position that was adopted prior to the bend........a lot of drivers tend to stay tucked-in right through a bend.....'over-steering' I call it....makes the car less stable too..much better to feed off towards the outside again.

This sort of thing can be done at any speed.......so is not the preserve of the 'go-faster brigade'......[check out 'Roadcraft' for nice diagrams?]

Put an extra few psi in the tyres helps as well....keep the ratio front-to-rear the same, however, or the 'handling' will change.


my two pennyworth?

True for petrol engines, but diesel engines don't have the same engine braking.

alastairq

True for petrol engines, but diesel engines don't have the same engine braking.

They do...to a degree.....petrol engines generally having less 'engine-braking' than diesel......

therefore, with a diseasel engine, the distance covered 'off-the-gas,will be less...

but a diesel engine still has stronger 'engine-braking' at higher revs...less at lower revs.....[which is why an exhaust brake is 'stronger' at higher revs....schitmatic gearboxes actually downshifting with exhaust brake on, esp. on snoooze control...]

The main point I was trying to put across, that may be easy to grasp for many, is to to to see how far one can go [in top gear?] without resorting to gas again......in my old Volvo 740, with it's tank engine, the sheer weight [and momentum ] meant that, to slow from 60 to 30 took more than half a mile........nice if I knew I would have to slow......not easy on an unfamiliar road....

mikey72

alastairq wrote: »

They do...to a degree.....petrol engines generally having less 'engine-braking' than diesel......

therefore, with a diseasel engine, the distance covered 'off-the-gas,will be less...

but a diesel engine still has stronger 'engine-braking' at higher revs...less at lower revs.....[which is why an exhaust brake is 'stronger' at higher revs....schitmatic gearboxes actually downshifting with exhaust brake on, esp. on snoooze control...]

The main point I was trying to put across, that may be easy to grasp for many, is to to to see how far one can go [in top gear?] without resorting to gas again......in my old Volvo 740, with it's tank engine, the sheer weight [and momentum ] meant that, to slow from 60 to 30 took more than half a mile........nice if I knew I would have to slow......not easy on an unfamiliar road....

You've got that the wrong way round. there is less engine braking on diesels, more with petrol. But you are right in that everyone should try seeing how long it takes to stop when thye've lifted off.

surfsister

almillar wrote: »

surfsister - there isn't one speed that all cars are most economical at. There also isn't a time when all cars should go up into top gear. It depends on type of engine (petrol/diesel just for starters), the gear ratios, drag, and of course the way you're trying to drive.
For example, if you're trying to merge onto a motorway, you should use the revs more and stay in 4th to accelerate, instead of changing early into 5th, and not getting the power. But if you're travelling at, I guess, a constant 50mph on a flat road, you should be in 5th instead of 4th, where the engine would be spinning unnecessarily fast.
There are only general tips, and you need to use your own judgement for your own car.

thanks for the reply

Lum

mikey72 wrote: »

You've got that the wrong way round. there is less engine braking on diesels, more with petrol. But you are right in that everyone should try seeing how long it takes to stop when thye've lifted off.

Also worth figuring out how long it takes to drop from, say, 70 to 50 and lifting off at an appropriate point before the speed limit changes, aiming to be at 50 by the time you reach the sign (or the camera 100 yards after the sign, if you're feeling naughty)

almillar

Diesels do, of course have engine braking, as do petrols. Engine braking varies between engines though, and turbo cars for example tend to have less engine braking than non turbos. As above, diesels do tend to have less engine braking than the more highly strung petrol engines. For all engines you get more engine braking the higher the revs, as you'll know if you've accidentally changed down into 2nd instead of 4th or something!

mikey72

almillar wrote: »

Diesels do, of course have engine braking, as do petrols. Engine braking varies between engines though, and turbo cars for example tend to have less engine braking than non turbos. As above, diesels do tend to have less engine braking than the more highly strung petrol engines. For all engines you get more engine braking the higher the revs, as you'll know if you've accidentally changed down into 2nd instead of 4th or something!

How does engine braking on a diesel work? Without any throttle body to restrict airflow?

alastairq

by cutting the fuel supply...in my experience, diesels, with their much higher compression ratios, have greater 'braking' effect than the equivalent petrol engines....it is the compression that creates the braking effect.

However, what also must be allowed for, is the differences in gearing, like-for-like.....and the differences in the rev ranges.

Diesel engines also tend to have more mass, heavier flywheels, etc, and coupled with low[er] revs, give the impression of lacking engine braking...compared to petrol.

Disiesel engines , by having greater mass, will provide greater momentum.....like my old Volvo..[admittedly a petrol, but what a mass!]....

This can be useful, and utilised by a fuel-conscious driver... by coming ''off the gas'' even earlier when approaching something that needs a speed reduction.


However, I do not recommend 'using the gears' to slow a vehicle...ie engaging progressively higher gears to use engine-braking effects.

[that's what the brakes are for]....with but one exception....and that is, when I wish to exercise control over the speed of the vehicle, going downhill!

In that instance, my primary objective is to prevent the vehicle running away, and in the process, to preserve my brakes...ie not over-heat them.

All to be achieved without allowing the engine to over-rev!


To that end, I found petrol engines [in a big car] to be less successful at holding me back through engine braking, than a similar, [weightwise] Land-rover turbot disiesel. [to be fair, both capable of in excess of 90mph...so gearing might not contribute as much as I'd have liked]



In the end, petrol or diesel, as I've mentioned before, it is for the individual driver to experiment....see what works, what does not.

There's a lot more fun to be had out of driving, than simply seeking to exceed the speed limit.