Mpg discussion and mpg/vehicle range records

[Suzie]

60mph is not necessarily the best speed (or even 100km/h which cars tend to be optimised for) where you just get in to top gear because for practical driving you have to take into account the power consumption of on board systems such as aircon, radio, headlights, etc. Increasing speed to reduce your journey time can significantly reduce the time that all the ancilliary equipment is running - cars are a lot more aerodynamic nowadays.

[Horsetan]

60mph is not necessarily the best speed (or even 100km/h which cars tend to be optimised for) where you just get in to top gear because for practical driving you have to take into account the power consumption of on board systems such as aircon, radio, headlights, etc. Increasing speed to reduce your journey time can significantly reduce the time that all the ancilliary equipment is running - cars are a lot more aerodynamic nowadays.

 

This is something to be taken into account, but I think it does depend on how your car was geared in the first place, and how well or otherwise it can cope with top gear from low speeds.

 

In my old 1983 635CSi, that was a 4-speed auto petrol and "lock-up top" (4th range) didn't kick in until about 57-58mph. It was impossible to run it in 4th below that speed as the gearbox automatically shifted downwards.

 

The 2003 Bora is a 5-speed manual diesel, and the characteristics of that mean it will run in top (5th) at 30mph and above. 60mph in top is the sort of speed that seems to require very little effort to maintain, regardless of the on-board systems you might have on the go. I don't really see any profit in going any quicker; I still get there all the same.

[Dunsignalling]

Most people don't seem to know this though! Your totally right!

They think that their maths proves it untrue even.

For eg;

Say you have a car capable of 60mpg top end. You drive it up a hill averaging 20mpg to get up, then you go back down the hill averaging 2,500mpg. Then car's computer would give the combined average as near to 40mpg.

But by their maths and lodgic; 40 + 2,500 = 2,540mpg / 2 trips (one up & one down) = 1,270mpg And the yet the display says 39.9mpg so they conclude their maths has proved the super high descent mpg as totally wrong!

 

The real logic, inline with your words John is; If you drive up a long long hill at 20mpg for 20 miles, using 1 gallon and then turn off the engine and roll back. You will have travelled 40miles on 1 gallon. But with the engine running in over run mode, it's used several tea spoons of fuel on the way down. Hence a reading like 39.9mph

On the really steep bits of some hills, needing third gear or below, the real-time fuel consumption read out gets to nearer to 10 than 20 even on my 1.6 diesel. 

 

As you point out, the over-run mode means that a small quantity of fuel is still admitted to the engine for cylinder lubrication purposes, so the downhill reading is not going to be precise. I think also that the Engine Management system judges the amount according to engine temperature (at least on some makes), introducing a further variable.

 

John

[MJI]

Hope you kept to the 40 mph speed limit.

 

What 40mph speed limit?

[Dunsignalling]

60mph is not necessarily the best speed (or even 100km/h which cars tend to be optimised for) where you just get in to top gear because for practical driving you have to take into account the power consumption of on board systems such as aircon, radio, headlights, etc. Increasing speed to reduce your journey time can significantly reduce the time that all the ancilliary equipment is running - cars are a lot more aerodynamic nowadays.

Gearing comes into it more than many realise, with many modern vehicles having tall gearing in 5th or 6th, effectively what we oldies used to call overdrive.

 

On my own 1.6 Turbo diesel, other than when coasting downhill, putting it in 5th at much under 45mph will usually result in the trip computer registering an increase  in the real-time consumption over what it had been doing in 4th.

 

By contrast, the over-run mode of the fuel injection operates to a quite pronounced degree when lifting off at fairly high speed (say 70-80mph), meaning that the fuel penalty for putting ones foot down is often not as great as one might expect. This using, as far as possible, the diesel driving technique of trying to have power on or off and minimising the use of a feathered throttle.

 

After a few miles of moderately illegal speed in keeping up with motorway traffic flow, I have been surprised to see that the average consumption mode read-out hasn't risen at all.     

Edited March 13, 2017 by Dunsignalling

[w124bob]

1973 Rover 3.5 litre V8. 23mpg downhill with a strong tailwind !!!!

 

1999 Ford Galaxy 2.3 Petrol. 36mpg Wigan - Taunton, all motorway @ 65 mph average

 

Kilometres & litres / km, not got a clue - meaningless french units to me !!

 

Brit15

Rover V8 P5B saloon or coupe or a P6? Must have been galeforce is all I can say!

[Nearholmer]

2005 VW Golf Plus 1.9L diesel, set at, I think, 115hp, currently reading (18 months or so) average 53mpg.

 

This is based on a very high % short runs (c15 mins), and on the rare occasions when I drive on a long run, rather than go by train, I like to watch the long term average climb ....... I've had it up to 70mpg when going to Cornwall or France, and I kept it at 60mpg for months doing short runs ........ what has "blown it" had been using the car during busier times of day; I used only to use it before anyone sensible was awake!

 

In short, to get fuel economy, drive fairly gently, on empty roads ....... it's increasing the top speed, and making more than minimal brake applications that gobble energy. The speed thing is, of course, a square-law effect, and the square of 70 is over a third bigger than the square of 60.

 

Kevin

[APOLLO]

Rover V8 P5B saloon or coupe or a P6? Must have been galeforce is all I can say!

 

P5B V8 Saloon. I once did actually calculate 24 mpg on a longish run from York to Newcastle up the A1 back in the mid 1980's.. Best these days is around 18 - 20 mpg. I only use her locally now. She runs better on supermarket 95 ron than she ever did on 4 star. (she was designed to run on 5 star !!). I use a petrol additive (Redex lead replacement).

 

Best mpg car I ever had was a new (1989) Peugeot 405 non turbo diesel. 54 mpg average. Lovely car.

 

Brit15

 

Brit15

[Ian Smeeton]

My '06 Focus gives me an average of about 48 mpg around and about. (We are out in the sticks, so no rel town driving).

 

On a good run I will get 60 -65 mpg (Grantham to Glasgow, say)

 

It is 3.5 miles to work, and when the weather is half way decent, I use the bicycle. I did reset the trip computer one day, just to see what it was costing me to get to work & back by car.

 

I only got 28mpg!

 

Back to the bike, sharpish.

 

Regards

 

Ian

[Red Baron]

Best on a short run  60.7  - Preston to Mcr.

 

General longer runs  56mpg  as i get bored of being careful.

 

2016  BMW 730LD

 

Edited March 13, 2017 by Red Baron

[APOLLO]

Yep, Wife has been using the Galaxy over winter to work, 7 miles each way, rural main road, no traffic, 26 MPG !!!!!!!!!!!!!!!

 

Must buy her a bike !!!

 

Brit15

[Jol Wilkinson]

Our previous Peugeot 308 2.0D returned 55.3 mpg over the time we had it.

 

The best range I ever saw was on a Peugeot 2.2D 406 Coupe (lovely car). I had just filled up on a business trip to Scotland and the trip computer showed 999 miles (it didn't do four digits). I had just had done a slowish few miles beforehand, so the "instantaneous" mpg had been quite high. The Coupe had quite a big tank while the 308 has a much smaller one and the best it shows is 600 miles. Longer runs are great but short trips, especially in wet or cold conditions, really pulls the economy down.

[Kickstart]

Hi

 

Varies a lot. Many years ago I had a Honda H100S (100cc 2 stroke air cooled single) and that did 95mpg pretty consistently, which was good given it was pretty much flat out everywhere (it did 58mph officially). During the fuel strikes I used my little Aprilia RS125 quite a bit, riding it VERY sedately. It managed to give 74.5mpg on one tank of fuel. Not sure it was worth it; riding at so low revs it vibrated a bit more, to the extent a few bolts vibrated loose.

 

My current Mazda MX5 2L managed 33mpg~34mpg in daily use, but that is a ~20 mile journey each way on A roads. A long steady run at 70mph gave 44.5mpg. The 2.5L 4wd Jaguar X Type we used to have gave 28mpg in normal use on the trip computer but worked out at 26mpg when calculated; it did manage 40mpg on the trip computer it driven gently on the motorway.

 

The Maserati 222E managed 18mpg in normal use. Not sure how accurate the milometer is. The old Alfa 33 I used when working in Belgium gave 39mpg sitting at about 90 on the motorways, but barely 20mpg on short journeys.

 

Odd one is how towing affected fuel consumption on various cars. Old Alfa 75 TS we had actually managed better fuel consumption towing the bike trailer. The pair of 155 2Ls we had were no worse when towing that when driven normally. The Jaguar used a load more fuel towing , as did the BMW 318.

 

That knocks the optimum 56mph theory into touch.

 

Not sure it is a real theory, rather just a nice round figure that is the A road speed limit in quite a few European countries and hence used for the tests. Because it isn't a round figure in miles per hour some people seem to think it is a magical figure for fuel economy.

 

The best mpg figures would not be achieved using a full tank.

While probably true, the difference in remarkably little, especially in road vehicles with not great aerodynamics. As a rule of thumb you need 1% of the vehicles weight in pounds as pounds of thrust to overcome rolling resistance, which is what the weight affects. This is a tiny amount compared to the thrust required to overcome drag. OK, more weight means more power (and fuel) to accelerate / go up a hill, but you gain that back decellerating / going down hill (assuming you are not using the brakes).

 

All the best

 

Katy

[jjb1970]

The extra urban test average speed is less than 40mph although it includes a short bit of over 70mph.

 

In terms of aerodynamics, new cars are not necessarily more aerodynamic. There was a period in the 80's when low drag figures became one of those marketing hooks (a bit like the MP count of digital cameras) and cars like the Audi 100 of the early 80's would still be considered aerodynamic today (if I remember right, Audi achieved a coefficient of 0.3). If anything typical drag coefficients have probably gone up thanks to the increasing popularity of SUVs which are less aerodynamic than many family cars of the 80's and 90's.

 

The relationship between engine power and wind resistance is exponential, not linear, and at anything above a modest canter it is drag which requires engine power to overcome (unless you're going uphill or towing). Gearing is important, my wife had an Audi A1 TDi and we also found that real world economy was abysmal relative to official figures largely thanks to a five speed gear box with widely spaced ratios clearly set up to give a good result in test conditions at the expense of sucking all life out of the power train with the result that to make decent pace you had to work the engine hard. I've driven the same 1.6TDi with a six speed gear box in the Audi A3 and despite being a bigger car it felt quite so much more lively than in the A1, chalk and cheese. That said, as speed goes up the amount of power needed to overcome drag increase hugely.

[Red Baron]

The extra urban test average speed is less than 40mph although it includes a short bit of over 70mph.

 

In terms of aerodynamics, new cars are not necessarily more aerodynamic. There was a period in the 80's when low drag figures became one of those marketing hooks (a bit like the MP count of digital cameras) and cars like the Audi 100 of the early 80's would still be considered aerodynamic today (if I remember right, Audi achieved a coefficient of 0.3). If anything typical drag coefficients have probably gone up thanks to the increasing popularity of SUVs which are less aerodynamic than many family cars of the 80's and 90's.

 

The relationship between engine power and wind resistance is exponential, not linear, and at anything above a modest canter it is drag which requires engine power to overcome (unless you're going uphill or towing). Gearing is important, my wife had an Audi A1 TDi and we also found that real world economy was abysmal relative to official figures largely thanks to a five speed gear box with widely spaced ratios clearly set up to give a good result in test conditions at the expense of sucking all life out of the power train with the result that to make decent pace you had to work the engine hard. I've driven the same 1.6TDi with a six speed gear box in the Audi A3 and despite being a bigger car it felt quite so much more lively than in the A1, chalk and cheese. That said, as speed goes up the amount of power needed to overcome drag increase hugely.

 

Sorry but your Aero knowledge needs an update

 

 Even my huge 7er has a CD of 0.24...   the  3yr old current shape X5 is 0.31    however the other factor is economy on runs is the 7/8/9/10 speed gearboxes allowing barely tickover at motorway speeds.

[leopardml2341]

17 mpg in this:

 

 

Which, I'm told is quite good!

 

600 cubic in engine, 7t 5cwt unladen, 4speed box, single speed diff.

 

Max recorded speed, 67mph.

Edited March 13, 2017 by leopardml2341

[jjb1970]

Sorry but your Aero knowledge needs an update

 

 Even my huge 7er has a CD of 0.24...   the  3yr old current shape X5 is 0.31    however the other factor is economy on runs is the 7/8/9/10 speed gearboxes allowing barely tickover at motorway speeds.

 

Agree on the efficiency improvement offered by modern automatic or sequential gear boxes.

[uax6]

Does anyone still run a vacuum gauge? I've got one lurking in the shed that I keep thinking about fitting to the van. Drilling the manifold keeps putting me off, but as it sounds like the existing one is cracked I might find another and pre-drill for it. My only concern is that I'll start becoming obsessed with getting the highest possible vacuum reading.....

 

Andy G

[Nearholmer]

Regarding the optimum speed for energy efficiency ......... the optimum speed surely isn't 56mph, it is "really, really slow", or, put another way "barely moving at all", and this applies irrespective of how heavy/light, streamlined/draggy etc the vehicle is.

 

But, no practical vehicle is optimised for energy efficiency. Most cars are, I guess, engineered for optimum saleability, where saleability is some ever-swirling function of fuel economy, spaciousness, safety, sexy-lookingness, self-perception-enhancingness, etc etc. Whopping great 4x4 currently seem to have high saleability, and that surely isn't because they are optimised for fuel efficiency.

 

OK. Rant suspended.

 

Did I mention that my first car was a 2CV? That was really, really slow, and, as a result, really fuel-efficient, even though the engine technology was closely related to that of a 1938 BMW motorbike.

 

K

[Ian J.]

Trouble is, you can't keep going downhill forever.   

 

John

 

The trick to keeping going down is to miss the ground...

 

(HHGTTG)

[stewartingram]

Does anyone still run a vacuum gauge? I've got one lurking in the shed that I keep thinking about fitting to the van. Drilling the manifold keeps putting me off, but as it sounds like the existing one is cracked I might find another and pre-drill for it. My only concern is that I'll start becoming obsessed with getting the highest possible vacuum reading.....

 

Andy G

 

I fitted one to my 1st car (Austin A30, around 1968-70) and learnt a lot about economy driving. Managed to get regular 48mpg out of it too! Since 200 I've been on lpg, and changed my habits to big Rover autos (827s followed by 75). The low fuel cost had made me less frugal and I enjoy the performance of the cars more now - and the comfort. The 75 I've just retired gave me 32mpg local and 42mpg on a journey, I do wonder what I would have got if my habits hadn't changed? Maybe I'll try with the latest 75?

 

Stewart

[MJI]

Hi

 

Varies a lot. Many years ago I had a Honda H100S (100cc 2 stroke air cooled single) and that did 95mpg pretty consistently, which was good given it was pretty much flat out everywhere (it did 58mph officially). During the fuel strikes I used my little Aprilia RS125 quite a bit, riding it VERY sedately. It managed to give 74.5mpg on one tank of fuel. Not sure it was worth it; riding at so low revs it vibrated a bit more, to the extent a few bolts vibrated loose.

 

My current Mazda MX5 2L managed 33mpg~34mpg in daily use, but that is a ~20 mile journey each way on A roads. A long steady run at 70mph gave 44.5mpg. The 2.5L 4wd Jaguar X Type we used to have gave 28mpg in normal use on the trip computer but worked out at 26mpg when calculated; it did manage 40mpg on the trip computer it driven gently on the motorway.

 

The Maserati 222E managed 18mpg in normal use. Not sure how accurate the milometer is. The old Alfa 33 I used when working in Belgium gave 39mpg sitting at about 90 on the motorways, but barely 20mpg on short journeys.

 

Odd one is how towing affected fuel consumption on various cars. Old Alfa 75 TS we had actually managed better fuel consumption towing the bike trailer. The pair of 155 2Ls we had were no worse when towing that when driven normally. The Jaguar used a load more fuel towing , as did the BMW 318.

 

 

Not sure it is a real theory, rather just a nice round figure that is the A road speed limit in quite a few European countries and hence used for the tests. Because it isn't a round figure in miles per hour some people seem to think it is a magical figure for fuel economy.

 

 

While probably true, the difference in remarkably little, especially in road vehicles with not great aerodynamics. As a rule of thumb you need 1% of the vehicles weight in pounds as pounds of thrust to overcome rolling resistance, which is what the weight affects. This is a tiny amount compared to the thrust required to overcome drag. OK, more weight means more power (and fuel) to accelerate / go up a hill, but you gain that back decellerating / going down hill (assuming you are not using the brakes).

 

All the best

 

Katy

 

I had a 1978 GP100 but that used to get 60s or 70s per gallon, but its maximum speed was a lot higher than your H100 (8 at the front).

 

My 250s were not much thirstier

 

My worst ever car MPG was towing a caravan, nearly empty after 110 or so miles, 15 or so solo, hence the 11 mpg.

 

However hill climbing with a van on the back and no worries about fuel consumption (45p a litre) was relaxing.

 

I have a Diesel car now and I can get that down in the low 20s if I want. (5 cylinder lump running somewhere in the 170s), sold the van the year before I bought this.

[MJI]

The extra urban test average speed is less than 40mph although it includes a short bit of over 70mph.

 

In terms of aerodynamics, new cars are not necessarily more aerodynamic. There was a period in the 80's when low drag figures became one of those marketing hooks (a bit like the MP count of digital cameras) and cars like the Audi 100 of the early 80's would still be considered aerodynamic today (if I remember right, Audi achieved a coefficient of 0.3). If anything typical drag coefficients have probably gone up thanks to the increasing popularity of SUVs which are less aerodynamic than many family cars of the 80's and 90's.

 

The relationship between engine power and wind resistance is exponential, not linear, and at anything above a modest canter it is drag which requires engine power to overcome (unless you're going uphill or towing). Gearing is important, my wife had an Audi A1 TDi and we also found that real world economy was abysmal relative to official figures largely thanks to a five speed gear box with widely spaced ratios clearly set up to give a good result in test conditions at the expense of sucking all life out of the power train with the result that to make decent pace you had to work the engine hard. I've driven the same 1.6TDi with a six speed gear box in the Audi A3 and despite being a bigger car it felt quite so much more lively than in the A1, chalk and cheese. That said, as speed goes up the amount of power needed to overcome drag increase hugely.

 

Big Opels/Vauxhalls were very aerodynamic much better than newer cars. Real fast road cars, I had a 2.0 Carlton and I could get 35mpg out of it not going slow.

[Dunsignalling]

Regarding the optimum speed for energy efficiency ......... the optimum speed surely isn't 56mph, it is "really, really slow", or, put another way "barely moving at all", and this applies irrespective of how heavy/light, streamlined/draggy etc the vehicle is.

 

But, no practical vehicle is optimised for energy efficiency. Most cars are, I guess, engineered for optimum saleability, where saleability is some ever-swirling function of fuel economy, spaciousness, safety, sexy-lookingness, self-perception-enhancingness, etc etc. Whopping great 4x4 currently seem to have high saleability, and that surely isn't because they are optimised for fuel efficiency.

 

OK. Rant suspended.

 

Did I mention that my first car was a 2CV? That was really, really slow, and, as a result, really fuel-efficient, even though the engine technology was closely related to that of a 1938 BMW motorbike.

 

K

Maybe not absolutely dead slow.

 

I recently drove my Peugeot (1.6 Hdi estate) from home to the outskirts of Taunton (18 miles) immediately after filling up and zeroing the trip. Fine dry day but loads of slow but freely moving traffic meant I did almost the whole trip at a steady 40mph in fourth gear (out of five) - recording 68 mpg on dashboard, the best I've ever seen from it and 3mpg better than Parkers guide gives as its lowest consumption. Previous brimming tests suggested the trip computer reads a bit on the pessimistic side so it may have just touched the magic 70 mpg.

 

Wouldn't want to do it on a long journey, though............

 

John

[Kickstart]

I had a 1978 GP100 but that used to get 60s or 70s per gallon, but its maximum speed was a lot higher than your H100 (8 at the front).

Problem with the H100 is that the were very low geared (they were in effect a stretched moped engine). Peak power was at 6500rpm, but top speed was quite a bit over 8000rpm. At the time you couldn't get a smaller rear or larger front sprocket to fit and up the gearing a bit (there is a larger front available these days)

 

All the best

 

Katy