Fuel Saving Driving Techniques

Honest John Back Room » Motoring discussion
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Wed 29 Jan 2020 14:35
Fuel Saving Driving Techniques - Firmbutfair

One of the downsides of engaging 'cruise control' in your car is that it is uses more fuel than allowing the driver to have full control over the throttle opening. Assuming that you are travelling at a reasonable and legal speed on a dual carriageway or motorway and that you are not 'in a hurry', then a significant fuel saving can be made by allowing the car to gently gather speed (and momentum) on each downgrade, up to say 65 or 70 mph, and then try not to further depress your accelerator on the upgrade, such that the car progressively but slowly reduces speed on the following upgrade, resulting in the speed falling to maybe 55 or 50 mph at the end of the uphill gradient. The efficacy and benefit of this technique can be seen most clearly if you reset your Trip Computer to read cumulative average mpg immediately before reaching your intended cruising speed, at which point the trip computer will be at its most responsive to changes in throttle opening and it will be seen that the average mpg displayed will progressively increase. Switching between the cumulative average mpg and the instantaneous mpg settings of the Trip Computer will indicate how successful your 'fuel saving' technique is and whether you need to be more gentle or less so with your throttle opening adjustments. Admittedly, adoption of this driving style on main roads will irritate lorry drivers who like to cruise at a constant 56 to 62 mph uphill and down dale, but on dual carriageways or motorways they will usually have plenty of opportunity to overtake you. By using this technique on longer journeys in a number of conventional 5 door hatchbacks, I have been able see average mpg figures approaching or even occasionally exceeding the old NEDC ‘65.7 mpg combined’ economy from door to door in light traffic conditions in the daytime, when making my regular 35, 47 and 58 mile journeys in Essex and Cambs - both there and back (i.e. both with following and ‘head on’ prevailing winds) - two up plus luggage - in my current car.

Clearly, this technique works best in flat country regions such as Essex, Cambridge, Lincolnshire etc and relies upon the fact that in general motorways and dual carriageways are never laid flat for any significant distance but are, by EU law, laid with gradients no steeper than 1 in 20 (5%) and no flatter than 1 in 120 (0.8%) in order to aid the run off of rainwater and thus prevent the accumulation of surface rainwater that could lead to aquaplaning at high speeds.

Edited by Firmbutfair on 29/01/2020 at 14:19

Reply | Report as offensive | Link
Wed 29 Jan 2020 15:43
Fuel Saving Driving Techniques - Andrew-T

<< Clearly, this technique works best in flat country regions such as Essex, Cambridge, Lincolnshire etc >>

Except that in areas as flat as that, there are no hills to gain speed on! Basically the message is to drive on a half-closed throttle as much as possible - which means moderating your acceleration from standstill. If you watch your instantaneous mpg readout you will soon see when fuel is being guzzled. And to slow using engine braking when possible.

Reply | Report as offensive | Link
Wed 29 Jan 2020 17:11
Fuel Saving Driving Techniques - bathtub tom

One of the downsides of engaging 'cruise control' in your car is that it is uses more fuel than allowing the driver to have full control over the throttle opening

Every car I've driven with cruise control has done a better job at economy than I could ever manage without cruise control on and that's with me trying hard.

Reply | Report as offensive | Link
Wed 29 Jan 2020 17:50
Fuel Saving Driving Techniques - gordonbennet

It's not too difficult to beat the 'puter at fuel saving on lorries, due to sheer weight you can travel enormous distances with no throttle input at all making maximum use of terrain, most cars simply don't have the weight to overcome tyre friction to make as much use of terrain, and carefully timing junctions in order to avoid stopping at all isn't the huge fuel saver that it is for lorries.

Cruise can be a little crude sometimes, where a competent driver can see ahead and adjust driving to make the best use of throttle, cruise cannot do this.

Reply | Report as offensive | Link
Wed 29 Jan 2020 19:26
Fuel Saving Driving Techniques - Terry W

Driving on motorways or dual carriageways at a speed varying between 50mph and 70mph is going to be stressful. Continually:

  • overtaking lorries on down hill stretches, and
  • being overtaken on the uphill bits
  • frequent lane changes
  • frustrating other drivers

If you want to save fuel and drive safer aim for a constant 60-65 mph - a little faster than lorries but slower than most other traffic. Mostly lane 1, or lane 2 to overtake a lorry.

Reply | Report as offensive | Link
Wed 29 Jan 2020 19:39
Fuel Saving Driving Techniques - gordonbennet

I agree with you Terry W, i've driven lorries for decades but when in my car i do not like being in and among them if i can help it, 60 to 65 you will have to contend with coaches travelling at a genuine 62 mph, which get baulked by lorries so there will be times when you have to increase speed in order to not get involved.

Can't say as i'm that worried about an extra 5mpg from my cars, so i'd rather run at 70 or so and keep out of the way of large vehicles when possible.

If you cause hindrance to lorries by overtaking them downhill only to hold them up on inclines you will, as sure as eggs are eggs, by the second or third time find someone who will react badly...this is not a threat warning or anything of the sort, just common sense to not be an irritant on already overcrowded roads in this overpopulated island.

Reply | Report as offensive | Link
Wed 29 Jan 2020 19:58
Fuel Saving Driving Techniques - Bolt

just common sense to not be an irritant on already overcrowded roads in this overpopulated island.

lane hoggers should learn that as well, hard these days to stick to any speed due to lane hoggers, and those that speed up and slow down for no apparent reason, I think just to be a menace which a lot of motorway drivers are now....

Reply | Report as offensive | Link
Wed 29 Jan 2020 20:52
Fuel Saving Driving Techniques - misar

I also agree with Terry W.

The OP's technique might be an interesting experiment to try early on a Sunday morning with deserted roads. It makes no sense as a regular driving technique on most UK roads. I also suspect that on a modern car with all the latest fuel saving gadgetry (e.g. mild hybrid, cylinder deactivation, good torque at low revs) it makes b***** all difference. My current car has that and I am getting about 30% better mpg that its predecessor with identical driving technique and journeys. Both the same model (i.e. same size and weight) and same engine size (2 litre).

Reply | Report as offensive | Link
Wed 29 Jan 2020 21:00
Fuel Saving Driving Techniques - John F

Ride 'n' glide; i.e. slip into 'N' on descents and approaches to roundabouts, slip roads and traffic lights. Turn off engine if long wait. Imagine a raw egg between foot and accelerator. Ensure tyre pressures are at least the recommendation. Use engine and foot braking as little as possible, anticipate bends and watch for traffic ahead slowing to turn off. Don't follow too closely on slow busy motorways or you will always be either braking or accelerating.

Reply | Report as offensive | Link
Thu 30 Jan 2020 02:49
Fuel Saving Driving Techniques - Firmbutfair

I agree and sympathise with most of the views expressed by the forum here and I must say that I do frequently enjoy driving between 65 and 70 mph to keep clear of the lorries etc and the technique can be used just as easily at this elevated speed range, though the base level mpg clearly reduces and will not normally match the combined mpg figure of the NEDC laboratory test. However when the conditions are right for the 'gradient plus gravity technique' to be employed, I find that cruising at around 55 mph gives the best compromise or 'trade off' between good fuel economy and overly extended journey times. At this speed I find that many other vehicles, some quite powerful too, are quite happy to follow me in lane 1 for several miles before overtaking me and I very rarely need to move from lane 1 because most of the lorries are 'cruising' past me in lane 2 at between 56 and 62 mph.

The potential for significant fuel saving on longish journeys, that this technique offers, surprised me when I first discovered it about 9 years ago after buying a modern hatch-back with a fully functional trip computer. Contrary to some opinions, if your brakes are in good order and not permanently 'binding' then your car should readily gather speed from say 50 to 70 mph on even a 1 in 120 downgrade and the resultant significant increase (doubling) in stored kinetic energy, (which is proportional to velocity squared) contributes significantly to propelling your car up the following upgrade with little or no further increase in throttle opening, accompanied only by the associated and inevitable reduction in speed back down to 50mph as the summit is approached. Needless to say, even driving non-aggressively in built up areas for a few days after one of these high mpg journeys soon brings the average down from say 68 mpg to 54 mpg which eventually bottoms out at around 48 mpg in these winter months - this is where the self-charging hybrid seems to offer better fuel economy.

Two close friends run an Auris Hybrid and a Yaris Hybrid respectively, and they both report consistently better local journey mpg than they were getting in similar previously owned petrol ICE engined cars but no improvement on longer faster journeys. Specifically the Yaris Hybrid owner claims 57 mpg over mixed driving in all but the worst winter weather.

Reply | Report as offensive | Link
Thu 30 Jan 2020 09:42
Fuel Saving Driving Techniques - Andrew-T

<< if your brakes are in good order and not permanently 'binding' then your car should readily gather speed from say 50 to 70 mph on even a 1 in 120 downgrade >>

I'm sorry, I just don't believe that figure. An gradient as slight as 1:120 would only slowly accelerate a train with solid wheels, so I doubt it would have much effect on a rubber-tyred car. I regularly drive 40 miles into north Wales, where I find familiar long downhill stretches which will maintain a speed of 40 or 50 mph, and those gradients are a lot more than 1 in 120 (I must check a map to find out what they really are).

My tyres are at recommended pressure too ... :-)

Reply | Report as offensive | Link
Thu 30 Jan 2020 09:59
Fuel Saving Driving Techniques - Andrew-T

I regularly drive 40 miles into north Wales, where I find familiar long downhill stretches which will maintain a speed of 40 or 50 mph, and those gradients are a lot more than 1 in 120 (I must check a map to find out what they really are).

I've checked the map: a kilometre straight of 1:25 will maintain about 55mph; a longer one of 1:44 will keep up about 40mph or a bit over. A good deal steeper than 1:120.

And my brakes don't bind either ... :-)

Reply | Report as offensive | Link
Thu 30 Jan 2020 15:14
Fuel Saving Driving Techniques - Andrew-T

<< a kilometre straight of 1:25 will maintain about 55mph; a longer one of 1:44 will keep up about 40mph or a bit over. A good deal steeper than 1:120. >>

F-but-F - we may have been at cross purposes here. My figures may be of more interest to John-F, who likes to coast down hills, and my measurements were under those conditions. But with modern cars doing that may save no fuel, because the ECU cuts it off when the 'throttle' closes, so more may be used when in neutral to prevent stalling.

But I still claim that a gradient of 1:120 will be of only marginal help against wind and rolling resistance.

Reply | Report as offensive | Link
Thu 30 Jan 2020 09:30
Fuel Saving Driving Techniques - Andrew-T

If you want to save fuel and drive safer aim for a constant 60-65 mph - a little faster than lorries but slower than most other traffic. Mostly lane 1, or lane 2 to overtake a lorry.

That pretty well sums up what I have done as second nature for decades, and is why I have had over 60mpg constantly from my (SWMBO's) present car. If circs demand, I will go faster to get round rolling roadblocks, for example, and I will not hog the middle lane, but overall I find it an unstressful way to drive on the Mway. (And of course 60-65 indicated is probably 55-60 real mph).

Edited by Andrew-T on 30/01/2020 at 09:31

Reply | Report as offensive | Link
Thu 30 Jan 2020 11:37
Fuel Saving Driving Techniques - SLO76
“ significant fuel saving can be made by allowing the car to gently gather speed (and momentum) on each downgrade, up to say 65 or 70 mph, and then try not to further depress your accelerator on the upgrade, such that the car progressively but slowly reduces speed on the following upgrade, resulting in the speed falling to maybe 55 or 50 mph at the end of the uphill gradient.”

This will save you a bit of fuel but it’s a real annoyance to coach and truck drivers behind you. I frequently have issues with drivers slowing on one particular steep section of motorway on leaving Glasgow where drivers slow in the central lane and refuse or are unable to pull into the normal driving lane (1) thus forcing me in a 50ft long near twenty tonne coach to slow on a steep hill which then causes congestion behind as I try to regain speed as more often than not lane one is full of people creeping along at 40-50mpg trying to eek out a few extra miles to the gallon. I notice a fair number of elderly hybrid and electric car owners in that lane desperately trying to justify spending £30k plus on a car that’ll save them nothing over their low annual mileage.

There should be no one in any of the overtaking lanes in a car or a van on a motorway doing less than 65mph. At ALL TIMES you should drive in lane one and should you need to overtake then you do so by putting your foot down to complete it as quickly as possible. I see countless drivers bumbling along the side of my bus at 1-2mph faster, sometimes they just sit at the same speed and linger right in my blind spot. They’ve no idea how dangerous it is and how irritating it is when I’m approaching something I need to overtake too. I’ve now taken to putting my rhs indicators on when anyone is idiotically hanging around instead of completing their overtake just to remind them to get a move on.

Edited by SLO76 on 30/01/2020 at 11:52

Reply | Report as offensive | Link
Thu 30 Jan 2020 13:25
Fuel Saving Driving Techniques - Engineer Andy

I agree entirely, SLO. A can't stand the 'foot-planters' who speed up quite a bit going downhill on roads (sometimes above the speed limit or enough so you cannot easily or safely overtake) or slow down accordingly going up non-steep inclines because they have no idea to keep up their speed to a constant and reasonable level when the road is flowing freely and conditions permit.

Whilst I am no speed demon, I am also no 'Captain Slow' either - I think that too many people seem to either be blissfully unaware of other road users when driving like the above, unduly slowly or not overtaking reasonably swiftly so not to hold up other vehicles in the other lanes, either that or they don't give a rat's backside.

The daft thing is that many people, driving slowly on local roads often drive in too high a gear and labour the engine, especially when they do need to accelerate, ending up using more fuel than if they were driving in a lower gear and perhaps even causing undue wear on the engine.

Doing so, especially when turning out of a junction or overtaking, can also be inherrantly dangerous for all concerned. Often, the same people are not attentive drivers generally and either don't signal, signal and go without looking/or knowing/caring what the consequences of 'just going for it' are, or all of the above.

The main fuel saving driving technique I advocate is driving defensively, anticipating others and situations, and keeping a good eye on the road, not just the next 100yds ahead, but everywhere, including in the far distance so speed and braking (including engine braking/coasting/backing off the gas [in gear]) can be correctly judged so that you only need to come to a complete halt/go into low gear rarely but without ticking off everyone behind by crawling.

I'm no driving guru, but from talking to many people over the years, I've managed to eek out 10-15% more mpg in both my cars (without annoying other road users by crawling) than the average for the type of driving done as per both the manufacturer's figures AND HJ's Real mpg numbers.

Reply | Report as offensive | Link
Thu 30 Jan 2020 14:50
Fuel Saving Driving Techniques - HGV ~ P Valentine

Paul Valentine

I too have driven in north wales and to be honest it is such a beautiful country that I really have no wish to travel faster as the windy roads are so enjoyable, I miss going up there.

Anyway, I usually stick to speed limits, for safety more then anything, but you should not be tempted to ride in neutral and in a truck you cannot do it without incurring a major fault on your test, you can dip the clutch while your foot is on the break and thus still being in control of the vehicle.

I cannot remember with the car test, but in the trucks you are taught to come to a stop with the break while dipping the clutch, and when you stop applying the handbrake, and then put the gear in neutral as the final step. ( clearly does not apply to automatics )

The idea being that if you should need to start again, then you only have to release the clutch and not have to " find a gear again".

Reply | Report as offensive | Link
Thu 30 Jan 2020 15:00
Fuel Saving Driving Techniques - galileo

Paul Valentine

I too have driven in north wales and to be honest it is such a beautiful country that I really have no wish to travel faster as the windy roads are so enjoyable, I miss going up there.

Anyway, I usually stick to speed limits, for safety more then anything, but you should not be tempted to ride in neutral and in a truck you cannot do it without incurring a major fault on your test, you can dip the clutch while your foot is on the break and thus still being in control of the vehicle.

I cannot remember with the car test, but in the trucks you are taught to come to a stop with the break while dipping the clutch, and when you stop applying the handbrake, and then put the gear in neutral as the final step. ( clearly does not apply to automatics )

The idea being that if you should need to start again, then you only have to release the clutch and not have to " find a gear again".

If you've put it in neutral you DO have to find a gear, if not, explain why.

Reply | Report as offensive | Link
Thu 30 Jan 2020 14:57
Fuel Saving Driving Techniques - Pinstripe

Lots of people report great mpg figures but nearly every trip computer I've ever checked properly (brim-to-brim, fuel in vs miles travelled) has nearly always exaggerated by about 10%.

Reply | Report as offensive | Link
Thu 30 Jan 2020 19:49
Fuel Saving Driving Techniques - Engineer Andy

Lots of people report great mpg figures but nearly every trip computer I've ever checked properly (brim-to-brim, fuel in vs miles travelled) has nearly always exaggerated by about 10%.

I only have ever used the 'brim-to-brim' method and never use my trip computer - of course it doesn't help than mine, for some reason, cannot show mpg but only shows either L/100km or L/100miles (I think).

Maybe because it was originally a car destined for Cyprus rather than the UK. I only know that 40mpg = 7.06L/100km, which is roughly what my car has done on average since I bought it 14 years ago.

I pay more attention to the miles left (odd why they included that and not mpg) on the 'remaining fuel' part of the trip computer, and I know that figure is not that accurate (always an over-estimate) as well. Just more of a guide to when I need to fill up again to be able to guestimate where the best (cheapest/most convenient) place to stop and fuel up.

Reply | Report as offensive | Link
Fri 31 Jan 2020 09:27
Fuel Saving Driving Techniques - Andrew-T

<< mine, for some reason, cannot show mpg but only shows either L/100km or L/100miles (I think). I only know that 40mpg = 7.06L/100km, which is roughly what my car has done on average since I bought it 14 years ago. >>

I thought all electronic readouts were switchable (Settings somewhere) ? Anyway, you can convert one number to the other by dividing it into 282 - good for your mental arithmetic.

Reply | Report as offensive | Link
Fri 31 Jan 2020 11:06
Fuel Saving Driving Techniques - sammy1

Buy an aerodynamic car in the first place instead of these brick shape SUVs and you are quids in before you apply any fuel saving techniques!

Reply | Report as offensive | Link
Fri 31 Jan 2020 11:14
Fuel Saving Driving Techniques - Bolt

Buy an aerodynamic car in the first place instead of these brick shape SUVs and you are quids in before you apply any fuel saving techniques!

Most dont buy for economy though, most buy for the looks and colour, some do complain of poor economy but they didn't check before buying what the consumption is.

as I said before most people buy because they want the motor and do not listen to advice...

Reply | Report as offensive | Link
Fri 31 Jan 2020 13:39
Fuel Saving Driving Techniques - Engineer Andy

<< mine, for some reason, cannot show mpg but only shows either L/100km or L/100miles (I think). I only know that 40mpg = 7.06L/100km, which is roughly what my car has done on average since I bought it 14 years ago. >>

I thought all electronic readouts were switchable (Settings somewhere) ? Anyway, you can convert one number to the other by dividing it into 282 - good for your mental arithmetic.

Mine is, just only between L/100km and L/100 miles. Perhaps an oversight from Mazda - perhaps they thought that because we now buy fuel in litres, then we don't use mpg any more. We still like to be awkward by mixing and matching our metric and imperal measurements!

Reply | Report as offensive | Link
Fri 31 Jan 2020 14:33
Fuel Saving Driving Techniques - Andrew-T

<< perhaps they thought that because we now buy fuel in litres, then we don't use mpg any more. We still like to be awkward by mixing and matching our metric and imperal measurements! >>

It's probably a small part of our instinctive anti-European tendencies. But no nation is as Imperial as the USA. They still do everything in pounds (weight) and gallons (and theirs is different from ours). And don't even mention metres - they agreed with Canada to go kilometric, but chickened out at the last minute so Canada went ahead anyway.

Reply | Report as offensive | Link
Fri 31 Jan 2020 13:21
Fuel Saving Driving Techniques - Leif

I am currently getting about 60 mpg per tank from my petrol 1.0 Polo, and in the summer I hit 70 mpg. This is calculated and not from the onboard computer. My commute is fairly hilly, and yes I do freewheel (in gear) down hills and I keep to a constant ~50 mph up hills. I find that going up hill I lose maybe 5 mpg on the average value, and then gain most of it back going down hill, so it averages out. For my car the consumption is heavily impacted by exceeding 50 mph, and by rain and cold (frosty) weather.

Another way to get more mpg is to anticipate by looking ahead. So when there is a queue of traffic ahead, slow down naturally rather than breaking hard, but don't crawl along as some do. Similarly when approaching a roundabout, slow naturally to a speed where you can nip on without stopping (in gear 2 or 3) if the traffic allows it, and it often does. Quite often I am overtaken approaching the roundabout, and then I shoot past the stationary car waiting to enter.

Generally I don't hold up traffic, but there are some people who clearly want to overtake. I find that by driving within the speed limits on rural roads it is more relaxing than speeding or going on motorways. Plus lower engine revs is better for the engine.

My onboard computer seems to overestimate mpg by about 5%, not a huge figure.

Reply | Report as offensive | Link
Fri 31 Jan 2020 14:06
Fuel Saving Driving Techniques - Ian_SW

I think choice of car has as much, if not more impact than driving style.

I had a Yaris hire car a couple of days ago (1.5 petrol). I drove over 250 miles in it over the day, without any real concern for fuel consumption as I wasn't paying and was running a bit late so pressing on a bit at times.

When I came to fill it up afterwards, it seemed to be remarkably cheap so I checked the on board computer. I had averaged over 60mph and also (according to it) just over 60mpg. From the amount of fuel I put in to fill it up and the number of miles it had done, that worked out as 57mpg. As the hire company delivered the car to me, I bet it had done 15-20 miles on top of my mileage since being filled up, so probably actually done fairly close to 60.

It does bring into question what the point is of the Yaris hybrid as an earlier post suggested a very similar fuel consumption to this.

I've never got over 50mpg in any 'Crossover' type vehicle, even diesels, yet these are incredibly popular, and then the owners spend the whole time driving them really gently to get a fuel consumption worse than they would if they drove something smaller and more aerodynamic without really caring.

Edited by SkodaIan on 31/01/2020 at 14:12

Reply | Report as offensive | Link
Fri 31 Jan 2020 14:37
Fuel Saving Driving Techniques - Andrew-T

<< My onboard computer seems to overestimate mpg by about 5%, not a huge figure. >>

Is that because it overmeasures the distance, or underestimates fuel usage? Mechanically-driven Pug odometers always seemed to overestimate distance by a few percent, but my current one (electronic) is pretty accurate.

Reply | Report as offensive | Link
Fri 31 Jan 2020 16:30
Fuel Saving Driving Techniques - concrete

The techniques for driving to conserve fuel and wear and tear are one in the same. Driver awareness is key. Slowing down naturally before junctions, lights etc to reduce braking. Accelerating smoothly away to the desired speed in the optimum gear. A light right foot. All pretty standard for the 53 years I have driven vehicles. I enjoy that driving style, which is why I appreciated the diesel cars. Also where you live makes a difference. When working I lived in North Yorkshire and worked all over the North and Scotland. Apart from the M62 corridor the traffic is less than the South and South east so fuel consumption is also less. The M74 is a fine motorway and relatively lightly used so it is eminently possible to cruise along with fewer vehicle to contend with. I regularly used to achieve over 60mpg from my Skoda Superb on these runs. In your own vehicle it makes so much sense to treat it well and drive carefully. It is win win all the way with the benefits of lower fuel costs, better tyre and brake wear, fewer repairs etc etc. Cheers Concrete

Reply | Report as offensive | Link