Range...

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Re: Range...

Post by Peter.N. »

That's cheating, I measured mine from the time the light stayed on :-D

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Re: Range...

Post by xmexclusive »

There is an assumption here that the odometer reading and the speed display must have the same error rate.
The speed display error is specified as a legal requirement to car manufacturers.
There is no reason to suppose that the manufacturers apply any error to the odometer.
An odometer will most likely read correctly with new full size tyres.

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Re: Range...

Post by davetherave »

I have just realised though that I did do the whole journey with roof bars on which probably didnt help the MPG, as well as having 3 sets of seats in the car on the way back!
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Re: Range...

Post by Northern_Mike »

xmexclusive wrote:There is an assumption here that the odometer reading and the speed display must have the same error rate.
The speed display error is specified as a legal requirement to car manufacturers.
John
There is no legal reason to make speedometers inaccurate.

he following information was obtained from website TheyWorkForYou.com
It refers to a statement in the House of Lords by Lord Whitty, and I quote:

"Both the EC Directive and the ECE Regulations lay down accuracy requirements to be applied at the time of vehicle approval for speedometers.
These requirements are that the indicated speed must not be more than 10% of the true speed + 4km/h. In production, however, a slightly different tolerance of 5% + 10km/h is applied. The requirements are also that the indicated speed must never be less than the true speed"
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Re: Range...

Post by Peter.N. »

I think they do though, practically everyone I have had has been 5% - 10% fast.

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Re: Range...

Post by xmexclusive »

That House of Lords quote has to be wrong in part or just typical politicians care for detail!!!!!!
At 100mph 10% of true speed plus 4kph is a speedo showing just over 12mph.
Again at 100mph tolerance of 5% plus 10kph is a speedo showing just over 110mph.

I suspect that that first item should actually be 100% not 10%.
I suspect that the second item shows that all production speedo's are set to read high.

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Re: Range...

Post by Stepto1 »

It just proves to me how hard it is to work out MPG at home.

What figures you trust is the key point.

It's so easy to believe the ones that give the best MPG rather then the ones that give a lower figure.

Also, some of he evidence on this thread is a little questionable.

Saying that a Xantia gives better MPG with two passengers and a load in the boot just flies in the face of physics and logic!

Next we'll be hearing that roof bars and a/c improve figures too.........
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Re: Range...

Post by Peter.N. »

My fuel consumption figures are confirmed by real world experience, I know how far it is from Axminster to Inverness, not just because my oddometer says so, and I know how much fuel I need to refill, but I agree there are many variable factors that can influence the results.

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Re: Range...

Post by Stepto1 »

I find the biggest problem is finding out the real distance travelled.

Nottingham to Plymouth -
By odometer in HDI-280 miles
By odometer in 16V Xantia -265 miles.
By Multimap - 262 miles.
By iPhone app -261 miles.

Which one do you go by?

Or speed?
Xantia says 90mph
GPS on Tom Tom, Garman handheld GPS AND IPhone -all read 80mph.

Then we are assuming the pump measures right.
AND that we know exactly how much fuel we have used.
AND that road conditions remain the same.
AND that the road is level and there is no rise or fall in altitude overall.
AND that there is no wind helping or hindering economy.
AND that we're not sitting behind trucks. (20% saving in fuel by some reseach)

By the way, driving on the motorway knowing that you are about to run out of fuel is bloody dangerous!

Even more so in a Xantia! If your engine stops and you're in the outside lane, you're trusting the accumulater to steer and brake you through heavy traffic and onto the hard shoulder.
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Re: Range...

Post by Peter.N. »

I drive in every way I can to aid economy, 60 mph or less most of the time, not exceeding 2000 rpm unnecessaraly, not braking unnecessarly and hanging on to the gear I am in to as low revs as possible and of course no rapid acceleration, also planning your route and the time that you take it, that is the only way of driving that will give really good economy and that is my normal method of driving.

I know that would bore many people to distraction but if money is tight that's how you have to drive - or get a smaller car and I don't like small cars. I did my fair share of boy racing in my youth but my current driving style suits me in retirement. I still do quite a lot of miles, we are off to the north of Scotland next week and will probably have done at least 2000 miles by the time we return. Last year we averaged 60.1 mpg for the whole trip in the 406 - if the readout can be believed but we were doing over 1000 miles on a tankful so that adds some creedance.

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Re: Range...

Post by Rhothgar »

Stepto1 wrote:It just proves to me how hard it is to work out MPG at home.
It's not difficult, Steve.

1) Fill your tank up to its limit. If in doubt, withdraw the dispensing pump and keep dribbling fuel in after the pump has first clicked until you see the level in the tank filler neck and until you can get no more in. Reset your trip meter before driving off.
2) Drive a set distance - the greater the distance the lesser the margin for error because of inconsistencies in different petrol pump settings. By this, I mean if you choose just to stop filling at one click. So use the whole tank before you fill up again.
3) When you need or feel the need to fill up again, use the same refilling procedure.

You can record this over a number of tanks.

Some of us on the forum have been recording MPG for years and so cannot be wrong. I use the Accufuel App from Appigo on my iPhone.
Stepto1 wrote:What figures you trust is the key point.
To an extent, maybe. But you are essentially comparing yourself against yourself. No-one else. It becomes irrelevant because if your own car's odometer is slightly out or you simply don't trust it, the inaccuracy is constant but you are building up a picture and that picture becomes more accurate as time goes by. In fact, you could start by recording your mileage and just putting 2 litres. Drive to the next petrol station and put another 2 litres in. Providing you eventually do a complete fill up, then the MPG will still be accurate (other than you are stopping more frequently and therefore using a lot more).
Stepto1 wrote:Also, some of he evidence on this thread is a little questionable.

Saying that a Xantia gives better MPG with two passengers and a load in the boot just flies in the face of physics and logic!
Not really. The poster may have driven in a steadier manner, he may not have driven the same route, if he had the traffic conditions may have be easier. There are a myriad of reasons why it may change.

Consider this - you never drive the same road twice! DickieG will understand what I am getting at.
Stepto1 wrote:Next we'll be hearing that roof bars and a/c improve figures too.........
And why not? It depends what speed you drive. Modern A/C setups have little effect on efficiency according to many sources.

What would make it unlikely is if you drive like a tw*t without roofbars and air con switched on and then you take your gran to Plymouth to visit long-lost relatives and it's a roasting hot day so you put the air con on then why not? It's a simple equation. Drive with more planning and observation and you will be rewarded with higher MPG.

I've read the figures recently somewhere but if you drive at 70mph, you use 20% more fuel than at 60mph. Drag becomes the main opponent to great MPG. Anything over 60mph is not good generally. I personally drive at a steady 70mph and my MPG figures speak volumes. If I slowed down to 56 mph (Extra-Urban), I would smash the original manufacturer's figures for my Xantia without a shadow of a doubt.

I actually recently purchased an Econometer which can be plumbed into any car's fuel supply and accurately measure fuel usage. Not set it up as yet but should do by the end of summer. I'll let everyone know how I get on with it.


Atmospheric conditions can also affect economy. In winter, cold air is inducted into the engine and this is supposed to be more efficient. This is why air ducts into the engine bay are best mounted to direct cooler air into the engine but let's not get side-tracked too much.
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Re: Range...

Post by Stepto1 »

I agree with much of the above accept that by comparing yourself against yourself there is no control to measure yourself against. You need a datum point or you could be miles out and would never know. This is the very basic rule of experimentation.

Also if you are not sure how far you have travelled then one half of the mpg equation is flawed.

As an engineer I'm well versed in what makes a machine efficient, weight does not, neither does drag.

Yes, a/c is better then having a window down but not having it on at all is even better.

I'm not knocking anyone on here but some of the mpg figures are simply too high.
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Re: Range...

Post by c.morewood »

I wish I had an easy way of showing you my Excel sheets. I have graphs going back to 1999 when the car was new which show the mpg achieved and 99% of the cost of running her.
"Fill your tank up to its limit. If in doubt, withdraw the dispensing pump and keep dribbling fuel in after the pump has first clicked until you see the level in the tank filler neck and until you can get no more in. Reset your trip meter before driving off."

I've always used this method.. letting the froth die down and the bubbles out of the filler neck before topping off.
When cost didn't matter and getting to work quickly was the point ( 1hr 30min 98 mile each way motorway commute) she was using about 48 ish mph sitting at 80 an maybe a bit more mph. this would have been 3 or 4 adult passengers as well.
Now I am and she is a bit older .. the commute is 15 miles (myself) and a mixture of country roads and dual carrigeway, (and cost is a factor) I'm averaging about 55mpg and trying to stay below 2000 RPM
The max I've ever got was about 59.5. Citroen claimed 62 if I remember correctly.

"I drive in every way I can to aid economy, 60 mph or less most of the time, not exceeding 2000 rpm unnecessaraly, not braking unnecessarly and hanging on to the gear I am in to as low revs as possible and of course no rapid acceleration, also planning your route and the time that you take it, that is the only way of driving that will give really good economy and that is my normal method of driving."

I agree Peter and can only add that using engine braking allows you to slow the car without using any fuel

My speedo under reads about 8 or 9 percent when comparing it against the satnav. but is the odometer connected to the speedo? My speedo has been playing up, I suspect a dry solder joint, when the temp gets about freezing sometimes not moving at all till I tap the dash, but the odometer still works and ticks over as normal.

"By the way, driving on the motorway knowing that you are about to run out of fuel is bloody dangerous!"

Agreed Stepto that's why I was taking the country roads to check out the maximum mileage... beside there's no motorway within a hundred miles of here!!
My point was to point out just how much extra fuel we were carrying around with us and its unneccessary to do the test again.

Rhothgar I'd like some more info on that econometer please.
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Re: Range...

Post by Stepto1 »

That's why I'm surprised that filling the tank to the brim, doing the drive, then filling up again is the best way of checking how much fuel is used. A meter would be a lot better. With a 65 litre tank that's the same as starting off with 3 full jerry cans in the boot.

Also, don't forget how much fuel the fuel lines hold and the fuel filter housing. On an HDI the filter housing must be about a litre.

My basic point is that many cars out there, mine included, state that they have done more miles then they really have and have been doing a lower speed then they really have been doing and therefore the calculated mpg figures are 'optimistic'.

That's all. I get all the hints and tips to get a few more mpg.

I drive at at least 80mph on the motorway as that means it takes me about four hours to get home. I don't want to sit in a car for any longer then that. Sitting at 60-70 on the motorway is like torture to me.

Still, at 80mph I'm still getting 40+mpg, which I am happy with. I can now get back on £40 rather then £60. Happy days.
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Re: Range...

Post by Rhothgar »

Stepto1 wrote:Also if you are not sure how far you have travelled then one half of the mpg equation is flawed.
Absolutely but if you want to measure your MPG to finite limits then you need to take your trip meter out and have it professionally calibrated by a company that calibrates Police Vehicles / Rally Cars and vehicles that require this level of accuracy. Personally I don't think it is worth the cost.
Stepto1 wrote:As an engineer I'm well versed in what makes a machine efficient, weight does not, neither does drag.
Not sure if you're joking here but I don't think you are. Weight affects energy used in acceleration only. Once at a constant velocity, it then has a neglible effect. However, drag is an entirely different matter. Of course, it depends on drag coefficients but we are not talking about vehicles with 'laminar' flow aerodynamics. A car with 1000bhp will not be twice as fast as an identical car with a 500bhp fitted and neither will a car with 200bhp and 100bhp within the same body.

Why do you think cars have a top speed? Drag in itself would have no effect on the efficiency of an engine but the engine has to work twice as hard to see an inversely-proportional increase in road speed.

If you double the power of a vehicle, it will reach 60mph by accelerating 1 to the square root of 2 faster i.e. if 0-60mph is 14.14 seconds with 70 bhp engine, increasing engine to 140bhp will reduce 0-60mph to 10 seconds. If the same car achieves 100mph, then its new top road speed will be 1 to the cubed root of 3 - approx 125.99mph.. Only drag can affect its road speed - nothing else.
Stepto1 wrote:Yes, a/c is better then having a window down but not having it on at all is even better.
That depends on drag created and disturbance to overall aerodynamics.
Stepto1 wrote:I'm not knocking anyone on here but some of the mpg figures are simply too high.
Not sure whose figures, you are referring to. I think someone quoted 67mpg. HDi's are supposed to do 62.8mpg so I personally do not see this as impossible with careful eco-driving. There are drivers out there that have extracted in the region of 80-100mpg on old Triump Spitfire which are supposed to only do about 35mpg.. These figures are not made up - they are from proper reliability trials.

Impossible is nothing!

The figures quoted by manufacturers and realistically attainable by the average driver if they are extremely careful which most are not - granted but that does not mean it cannot be achieved.

As a lad, I read an article once which identified where the 'circuit' was that manufacturers used to test their cars. It was a real world environment but I am sure that the manufacturers probably did their tests at 3am to avoid traffic problems. The combined figure consisted of 30mph over a set distance with a 56mph and 70 mph run in between the end. This was supposed to emulate a typical daily journey. Get in your car, set off, drive to work and home. All done in one run though and I would imagine they did it with pre-warmed engines too (at normal operating temperature).

One final thing - when I went to London last week and reported 52.5 mpg (not forgetting mine is a 1.9TD non-Hdi with a theoretical maximum of 53mpg at 56 mph), I filled up in the morning and didn't fill right up to the brim. I gave it 3 clicks. When I returned and filled up at the same filling station later that day, I filled it up higher. I think after 3 clicks it was only on 22.22 litres but I dribbled more in (24.67 litres to be precise) so my calculation was inaccurate in that I could have actually achieved 58.08mpg (had I stopped filling at 22.22 litres) But I am not that bothered because ultimately as more time passes it averages itself out over more tanks.

My overall average MPG since 27th June 2009 is still 42mpg and I do not see this increasing much unless I hyper-mill on every tank for the next few years.

I hope this clarifies a few points on my side. I know you have commented before that you did try eco-driving the other week but then got a BMW up your ass and it went out of the window.

A change of mindset may eventually see to it that your MPG does increase and you'll suffer from a lot less driving stress. Driving quick gets you nowhere fast. Trust me - I have undertaken tests myself which I will not record on this forum for obvious reasons but when I used to drive like an idiot - I perhaps got to the particular destination 10 minutes quicker over 42 miles than driving at 56mph.. The speed on the faster journey was incredibly fast and the amount of stress and concentration needed to do this is simply not worth it.

I am sure DickieG could had to this with his wealth of experience. Luckily, he had one major advantage of blues and twos!
Last edited by Rhothgar on 09 May 2012, 19:14, edited 1 time in total.
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