I decided to try a few experiments on fuel economy.

Equipment used:
VW Golf TDI 1.9
Mpg meter on Golf's dashboard
Tomtom One

Experiment one - what speed should I drive at?
I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
50mph = 47mpg
60mph = 47mpg
70mph = 40mpg
80mph = 33mpg
So that's where "at a steady 56" came from on that old Audi advert.
Wind resistance suddenly becomes more above 60?!? Anyone got a Physics degree? I do, but it was too long ago!

Experiment two - what's the most efficient route to take?
I tried four routes from home to work, driving with gentle acceleration, as constant a speed as possible, and never exceeding 60mph:
1: "Quickest route" on the Tomtom (mainly took motorways)
2: "Shortest route" on the Tomtom (took country roads and went through a few villages)
3: What looked like a fairly direct simple route on the map along A roads
4: What looked like a fairly direct simple route on the map along B roads

The data:
Route 1: 0.73 gallons = £3.35, 39 minutes
Route 2: 0.58 gallons = £2.66, 36 minutes
Route 3: 0.64 gallons = £2.93, 41 minutes
Route 4: 0.65 gallons = £2.98, 43 mniutes

Interesting - contrary to the Satnav instructions, the "shortest route" is much more economical than the "quickest route". Also the "quickest route" takes longer!

Experiment three - should I drive fast?
I took the best of the above four routes and drove it as fast as the car would go, to compare it with driving "sensibly" as above.

Sensible: 0.58 gallons = £2.66, 36 minutes
Fast: 0.74 gallons = £3.40, 28 minutes

So you only save 20% on fuel by being an annoying driver who gets in everyone's way, and pays more attention to the speedometer than the road ahead. I'll stick to going fast!

"Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
> I decided to try a few experiments on fuel economy.
>
> Equipment used:
> VW Golf TDI 1.9
> Mpg meter on Golf's dashboard
> Tomtom One
>
> Experiment one - what speed should I drive at?
> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
> 50mph = 47mpg
> 60mph = 47mpg
> 70mph = 40mpg
> 80mph = 33mpg
> So that's where "at a steady 56" came from on that old Audi advert.
> Wind resistance suddenly becomes more above 60?!? Anyone got a Physics
> degree? I do, but it was too long ago!
>
> Experiment two - what's the most efficient route to take?
> I tried four routes from home to work, driving with gentle acceleration,
> as constant a speed as possible, and never exceeding 60mph:
> 1: "Quickest route" on the Tomtom (mainly took motorways)
> 2: "Shortest route" on the Tomtom (took country roads and went through a
> few villages)
> 3: What looked like a fairly direct simple route on the map along A roads
> 4: What looked like a fairly direct simple route on the map along B roads
>
> The data:
> Route 1: 0.73 gallons = £3.35, 39 minutes
> Route 2: 0.58 gallons = £2.66, 36 minutes
> Route 3: 0.64 gallons = £2.93, 41 minutes
> Route 4: 0.65 gallons = £2.98, 43 mniutes
>
> Interesting - contrary to the Satnav instructions, the "shortest route" is
> much more economical than the "quickest route". Also the "quickest route"
> takes longer!
>
> Experiment three - should I drive fast?
> I took the best of the above four routes and drove it as fast as the car
> would go, to compare it with driving "sensibly" as above.
>
> Sensible: 0.58 gallons = £2.66, 36 minutes
> Fast: 0.74 gallons = £3.40, 28 minutes
>
> So you only save 20% on fuel by being an annoying driver who gets in
> everyone's way, and pays more attention to the speedometer than the road
> ahead. I'll stick to going fast!



The quickest route will always be slower if you don't drive at the speed
TomTom assumes, i.e. 70 mph on a motorway.

On Fri, 24 Jul 2009 19:59:48 +0100, pugwash <(E-Mail Removed)> wrote:

>
>
> "Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
>> I decided to try a few experiments on fuel economy.
>>
>> Equipment used:
>> VW Golf TDI 1.9
>> Mpg meter on Golf's dashboard
>> Tomtom One
>>
>> Experiment one - what speed should I drive at?
>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>> 50mph = 47mpg
>> 60mph = 47mpg
>> 70mph = 40mpg
>> 80mph = 33mpg
>> So that's where "at a steady 56" came from on that old Audi advert.
>> Wind resistance suddenly becomes more above 60?!? Anyone got a Physics
>> degree? I do, but it was too long ago!
>>
>> Experiment two - what's the most efficient route to take?
>> I tried four routes from home to work, driving with gentle acceleration,
>> as constant a speed as possible, and never exceeding 60mph:
>> 1: "Quickest route" on the Tomtom (mainly took motorways)
>> 2: "Shortest route" on the Tomtom (took country roads and went through a
>> few villages)
>> 3: What looked like a fairly direct simple route on the map along A roads
>> 4: What looked like a fairly direct simple route on the map along B roads
>>
>> The data:
>> Route 1: 0.73 gallons = £3.35, 39 minutes
>> Route 2: 0.58 gallons = £2.66, 36 minutes
>> Route 3: 0.64 gallons = £2.93, 41 minutes
>> Route 4: 0.65 gallons = £2.98, 43 mniutes
>>
>> Interesting - contrary to the Satnav instructions, the "shortest route" is
>> much more economical than the "quickest route". Also the "quickest route"
>> takes longer!
>>
>> Experiment three - should I drive fast?
>> I took the best of the above four routes and drove it as fast as the car
>> would go, to compare it with driving "sensibly" as above.
>>
>> Sensible: 0.58 gallons = £2.66, 36 minutes
>> Fast: 0.74 gallons = £3.40, 28 minutes
>>
>> So you only save 20% on fuel by being an annoying driver who gets in
>> everyone's way, and pays more attention to the speedometer than the road
>> ahead. I'll stick to going fast!
>
>
>
> The quickest route will always be slower if you don't drive at the speed
> TomTom assumes, i.e. 70 mph on a motorway.

What does it assume for an A and B road?


--
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One day a sweet little girl becomes puzzled about her origin.
"How did I get here, Mommy?" she asks.

Her mother replies, using a well-worn phrase, "Why God sent
you, Honey."

"And did God send you too, Mommy?" she continues.

"Yes, Sweetheart, he did."

"And Daddy, and Grandma and Grandpa, and their moms and
dads, too?"

"Yes, Honey, all of them, too."

The child shakes her head in disbelief. "Then you're telling me
there's been no sex in this family for over 200 years? No
wonder everyone is so grouchy!"

"Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk7vig04buhsv@i7...
> On Fri, 24 Jul 2009 19:59:48 +0100, pugwash <(E-Mail Removed)> wrote:
>
>>
>>
>> "Peter Hucker" <(E-Mail Removed)> wrote in message
>> newsp.uxk1y0r04buhsv@i7...
>>> I decided to try a few experiments on fuel economy.
>>>
>>> Equipment used:
>>> VW Golf TDI 1.9
>>> Mpg meter on Golf's dashboard
>>> Tomtom One
>>>
>>> Experiment one - what speed should I drive at?
>>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>>> 50mph = 47mpg
>>> 60mph = 47mpg
>>> 70mph = 40mpg
>>> 80mph = 33mpg
>>> So that's where "at a steady 56" came from on that old Audi advert.
>>> Wind resistance suddenly becomes more above 60?!? Anyone got a Physics
>>> degree? I do, but it was too long ago!
>>>
>>> Experiment two - what's the most efficient route to take?
>>> I tried four routes from home to work, driving with gentle acceleration,
>>> as constant a speed as possible, and never exceeding 60mph:
>>> 1: "Quickest route" on the Tomtom (mainly took motorways)
>>> 2: "Shortest route" on the Tomtom (took country roads and went through a
>>> few villages)
>>> 3: What looked like a fairly direct simple route on the map along A
>>> roads
>>> 4: What looked like a fairly direct simple route on the map along B
>>> roads
>>>
>>> The data:
>>> Route 1: 0.73 gallons = £3.35, 39 minutes
>>> Route 2: 0.58 gallons = £2.66, 36 minutes
>>> Route 3: 0.64 gallons = £2.93, 41 minutes
>>> Route 4: 0.65 gallons = £2.98, 43 mniutes
>>>
>>> Interesting - contrary to the Satnav instructions, the "shortest route"
>>> is
>>> much more economical than the "quickest route". Also the "quickest
>>> route"
>>> takes longer!
>>>
>>> Experiment three - should I drive fast?
>>> I took the best of the above four routes and drove it as fast as the car
>>> would go, to compare it with driving "sensibly" as above.
>>>
>>> Sensible: 0.58 gallons = £2.66, 36 minutes
>>> Fast: 0.74 gallons = £3.40, 28 minutes
>>>
>>> So you only save 20% on fuel by being an annoying driver who gets in
>>> everyone's way, and pays more attention to the speedometer than the road
>>> ahead. I'll stick to going fast!
>>
>>
>>
>> The quickest route will always be slower if you don't drive at the speed
>> TomTom assumes, i.e. 70 mph on a motorway.
>
> What does it assume for an A and B road?
>
>
> --


I believe it assumes whatever the speed limit assigned on the map is the
speed you'll drive at, then it applies any live traffic delays (if you
subscribe). Assuming of course the speed limit on it's map is correct -
which from my experience is not always true.

According to the rules, drag increases as the square of speed. So, all
else being equal you should use 4 times as much fuel at 60mph as you
do at 30 mph.

Of course, all is not equal. There must be an engine speed where the
engine is operating at its most efficient. This combined with the
overall gearing could tell a better story.

It would be interesting to know the engine RPM at the speeds that you
mention and perhaps the gear used.

"Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
>I decided to try a few experiments on fuel economy.
>
> Equipment used:
> VW Golf TDI 1.9
> Mpg meter on Golf's dashboard
> Tomtom One
>
> Experiment one - what speed should I drive at?
> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
> 50mph = 47mpg
> 60mph = 47mpg
> 70mph = 40mpg
> 80mph = 33mpg

quite good mpg, almost makes me consider buying a diesel car

"roarey" <(E-Mail Removed)> wrote in message news:FQDam.56832$(E-Mail Removed)2...
>
> "Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
>>I decided to try a few experiments on fuel economy.
>>
>> Equipment used:
>> VW Golf TDI 1.9
>> Mpg meter on Golf's dashboard
>> Tomtom One
>>
>> Experiment one - what speed should I drive at?
>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>> 50mph = 47mpg
>> 60mph = 47mpg
>> 70mph = 40mpg
>> 80mph = 33mpg
>
> quite good mpg, almost makes me consider buying a diesel car
>

That's not very good by modern diesel standards

--
Alex

"I laugh in the face of danger , then I hide until it goes away"

Dr Zoidberg wrote:
> "roarey" <(E-Mail Removed)> wrote in message news:FQDam.56832$(E-Mail Removed)2...
>> "Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
>>> I decided to try a few experiments on fuel economy.
>>>
>>> Equipment used:
>>> VW Golf TDI 1.9
>>> Mpg meter on Golf's dashboard
>>> Tomtom One
>>>
>>> Experiment one - what speed should I drive at?
>>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>>> 50mph = 47mpg
>>> 60mph = 47mpg
>>> 70mph = 40mpg
>>> 80mph = 33mpg
>> quite good mpg, almost makes me consider buying a diesel car
>>
>
> That's not very good by modern diesel standards

That's what I was thinking. My Octavia 2.0D with DSG can easily beat
that - with cruise on at a steady 65mph, it'll do mid 50s. I'm looking
forward to the new 1.6D that, on paper at least, promises to be
exceptional when it comes to economy.

There are plenty of good sized petrol cars that'll beat 47mpg.

"Silk" <(E-Mail Removed)> wrote in message news:h4fl2k$mo7$(E-Mail Removed)...
> Dr Zoidberg wrote:
>> "roarey" <(E-Mail Removed)> wrote in message news:FQDam.56832$(E-Mail Removed)2...
>>> "Peter Hucker" <(E-Mail Removed)> wrote in message newsp.uxk1y0r04buhsv@i7...
>>>> I decided to try a few experiments on fuel economy.
>>>>
>>>> Equipment used:
>>>> VW Golf TDI 1.9
>>>> Mpg meter on Golf's dashboard
>>>> Tomtom One
>>>>
>>>> Experiment one - what speed should I drive at?
>>>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>>>> 50mph = 47mpg
>>>> 60mph = 47mpg
>>>> 70mph = 40mpg
>>>> 80mph = 33mpg
>>> quite good mpg, almost makes me consider buying a diesel car
>>>
>>
>> That's not very good by modern diesel standards
>
> That's what I was thinking. My Octavia 2.0D with DSG can easily beat
> that - with cruise on at a steady 65mph, it'll do mid 50s.

I've now got a 1.6 diesel Bravo which at a steady 50 or 60 will be doing 70-80 mpg

> I'm looking
> forward to the new 1.6D that, on paper at least, promises to be
> exceptional when it comes to economy.

Yep.
On paper it's a smidge more economical than my Bravo but only having a five speed gearbox instead of six makes me think that in practice it won't be any better.
My average from new is a genuine 56mpg but on the last couple of full tanks I've got over 60 which is very good.
My Octy would typically do about 50-52 on a tank depending on how I'd driven which was still pretty impressive for a car that would also do a 9 second 0-60 (though obviously not returning 52mpg at the time)

>
> There are plenty of good sized petrol cars that'll beat 47mpg.

At a constant speed the instananeous figure would be at that level though it would be tricker to get that as long term average.

--
Alex

"I laugh in the face of danger , then I hide until it goes away"

"Dr Zoidberg" <AlexNOOOO!!!!!!!!@drzoidberg.co.uk> wrote in message
news:h4fpgt$r90$(E-Mail Removed)...
"Silk" <(E-Mail Removed)> wrote in message news:h4fl2k$mo7$(E-Mail Removed)...
> Dr Zoidberg wrote:
>> "roarey" <(E-Mail Removed)> wrote in message
>> news:FQDam.56832$(E-Mail Removed)2...
>>> "Peter Hucker" <(E-Mail Removed)> wrote in message
>>> newsp.uxk1y0r04buhsv@i7...
>>>> I decided to try a few experiments on fuel economy.
>>>>
>>>> Equipment used:
>>>> VW Golf TDI 1.9
>>>> Mpg meter on Golf's dashboard
>>>> Tomtom One
>>>>
>>>> Experiment one - what speed should I drive at?
>>>> I tried going at 50mph, 60mph, 70mph, and 80mph on the motorway.
>>>> 50mph = 47mpg
>>>> 60mph = 47mpg
>>>> 70mph = 40mpg
>>>> 80mph = 33mpg
>>> quite good mpg, almost makes me consider buying a diesel car
>>>
>>
>> That's not very good by modern diesel standards
>
> That's what I was thinking. My Octavia 2.0D with DSG can easily beat
> that - with cruise on at a steady 65mph, it'll do mid 50s.

I've now got a 1.6 diesel Bravo which at a steady 50 or 60 will be doing
70-80 mpg

> I'm looking
> forward to the new 1.6D that, on paper at least, promises to be
> exceptional when it comes to economy.

Yep.
On paper it's a smidge more economical than my Bravo but only having a five
speed gearbox instead of six makes me think that in practice it won't be any
better.
My average from new is a genuine 56mpg but on the last couple of full tanks
I've got over 60 which is very good.
My Octy would typically do about 50-52 on a tank depending on how I'd driven
which was still pretty impressive for a car that would also do a 9 second
0-60 (though obviously not returning 52mpg at the time)

>
> There are plenty of good sized petrol cars that'll beat 47mpg.

At a constant speed the instananeous figure would be at that level though it
would be tricker to get that as long term average.

--
Alex

"I laugh in the face of danger , then I hide until it goes away"

I run LPG and at around half the cost of petrol or diesel per litre I reckon
that I am getting high 70's low 80's equivalent £ for £. Might not get as
many miles per gallon but it is miles per £ I am more concerned with. I
average over 150 miles per £10 currently saving about £400 per 10k miles on
fuel alone and £15 road tax helps too.