Hi all,

I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the 
bidding commence for the fuel LOL). I've got to do a few trips betwen 
Liverpool, St Helens and Bolton between now and the weekend for work 
purposes. I'm self employed and have to work to earn so can use the petrol 
situation as an excuse.

For maximum economy what speed and/or RPM should I be looking to keep at on 
motorways? Am I right to assume I should chose motorway routes rather than 
stop-start normal road routes?

Thanks for your advice everybody :o)

Ben

"Ben"  wrote in message 
news:UroVe.24140$k22.4455@fe2.news.blueyonder.co.uk...

> Hi all,
>
> I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the 
> bidding commence for the fuel LOL). I've got to do a few trips betwen 
> Liverpool, St Helens and Bolton between now and the weekend for work 
> purposes. I'm self employed and have to work to earn so can use the petrol 
> situation as an excuse.
>
> For maximum economy what speed and/or RPM should I be looking to keep at 
> on motorways? Am I right to assume I should chose motorway routes rather 
> than stop-start normal road routes?
>
> Thanks for your advice everybody :o)



Take the train if you're that concerned?

Otherwise, there's no one answer.  Lowest speed in the highest gear without 
labouring.  Match the HGV.  If you drive with sensitivity to the throttle 
you'll be just fine.  If not, simply slowing down won't make much of a 
difference.

Check out my article about fuel consumption on my website.

-- 
The DervMan
www.dervman.com

Ben wrote:

> 
> Hi all,
> 
> I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the
> bidding commence for the fuel LOL). I've got to do a few trips betwen
> Liverpool, St Helens and Bolton between now and the weekend for work
> purposes. I'm self employed and have to work to earn so can use the petrol
> situation as an excuse.
> 
> For maximum economy what speed and/or RPM should I be looking to keep at on
> motorways? Am I right to assume I should chose motorway routes rather than
> stop-start normal road routes?
> 
> Thanks for your advice everybody :o)
> 
> Ben


You can drive at 50mph on the motorway, but unfortunately that will make
a nuisance for other motorists. However, you can get away with 60mph by
following Heavy Goods Vehicles that are restricted to 60mph anyway. 
Make sure that the tyre pressures are correct.

Johannes wrote:


> 
> 
> Ben wrote:
>> 
>> Hi all,
>> 
>> I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the
>> bidding commence for the fuel LOL). I've got to do a few trips betwen
>> Liverpool, St Helens and Bolton between now and the weekend for work
>> purposes. I'm self employed and have to work to earn so can use the
>> petrol situation as an excuse.
>> 
>> For maximum economy what speed and/or RPM should I be looking to keep at
>> on motorways? Am I right to assume I should chose motorway routes rather
>> than stop-start normal road routes?
>> 
>> Thanks for your advice everybody :o)
>> 
>> Ben
> 
> You can drive at 50mph on the motorway, but unfortunately that will make
> a nuisance for other motorists. However, you can get away with 60mph by
> following Heavy Goods Vehicles that are restricted to 60mph anyway.
> Make sure that the tyre pressures are correct.


Sound advice. Remember too that tracking that is way out will effect
economy. Make sure that all brakes release fully, eg no sticky calliper
pistons or handbrake cables. Empty the car of everything you don't need and
keep windows closed.

WRT driving, using the brakes wastes fuel, so anticipation is more important
than creeping a few miles an hour above your intended speed.

Chris

-- 
Remove prejudice to reply

"Chris Whelan"  wrote in message
news:JNwVe.4396$Q%2.3246@newsfe1-win.ntli.net...

> Johannes wrote:
>
> >
> >
> > Ben wrote:
> >>
> >> Hi all,
> >>
> >> I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the
> >> bidding commence for the fuel LOL). I've got to do a few trips betwen
> >> Liverpool, St Helens and Bolton between now and the weekend for work
> >> purposes. I'm self employed and have to work to earn so can use the
> >> petrol situation as an excuse.
> >>
> >> For maximum economy what speed and/or RPM should I be looking to keep
at
> >> on motorways? Am I right to assume I should chose motorway routes
rather
> >> than stop-start normal road routes?
> >>
> >> Thanks for your advice everybody :o)
> >>
> >> Ben
> >
> > You can drive at 50mph on the motorway, but unfortunately that will make
> > a nuisance for other motorists. However, you can get away with 60mph by
> > following Heavy Goods Vehicles that are restricted to 60mph anyway.
> > Make sure that the tyre pressures are correct.
>
> Sound advice. Remember too that tracking that is way out will effect
> economy. Make sure that all brakes release fully, eg no sticky calliper
> pistons or handbrake cables. Empty the car of everything you don't need
and
> keep windows closed.
>
> WRT driving, using the brakes wastes fuel, so anticipation is more
important
> than creeping a few miles an hour above your intended speed.


Open windows increase drag by about 10%, so if you need to drive with one
open, have it only down a jiffy.

Low tyre pressures, binding brakes, engine in poor tune, tracking parallel
in that order will lower your mpg the worst.

> For maximum economy what speed and/or RPM should I be looking to keep at
on
> motorways? Am I right to assume I should chose motorway routes rather than
> stop-start normal road routes?


Modern aerodynamic cars are best at about a steady 60mph in top gear.
Anything more brick shaped will be optimum slower. A van might be best at
steady 50mph, or even 45mph, if it's a particularly unaerodynamic with roof
rails.

Christian.

Christian McArdle wrote:

> 
> > For maximum economy what speed and/or RPM should I be looking to keep at
> on
> > motorways? Am I right to assume I should chose motorway routes rather than
> > stop-start normal road routes?
> 
> Modern aerodynamic cars are best at about a steady 60mph in top gear.
> Anything more brick shaped will be optimum slower. A van might be best at
> steady 50mph, or even 45mph, if it's a particularly unaerodynamic with roof
> rails.
> 
> Christian.



Aerodynamic resistance grows with the speed squared. So everything being
equal, 50mph is more economical than 60mph is more economical than 70mph
and so on. But the efficiency also depends on the rpm, hence having a good
gear ratio for the speed. My Saab has an instant mpg readout. (Why is it
called readout and nor writeout?). I certainly find that my Saab is very
economical at 50mph and that the consumption always increases (mpg decreases)
with speed, just as you would expect.

Aim for 52 mpg which is what I can get from a motorway trip at 60mph in my
1998 1.6 laguna (petrol).

Stu


"Johannes"  wrote in message
news:4326FE8F.52F7633A@spam-gets-slammed-sizefitter.com...

>
>
> Christian McArdle wrote:
> >
> > > For maximum economy what speed and/or RPM should I be looking to keep
at
> > on
> > > motorways? Am I right to assume I should chose motorway routes rather
than
> > > stop-start normal road routes?
> >
> > Modern aerodynamic cars are best at about a steady 60mph in top gear.
> > Anything more brick shaped will be optimum slower. A van might be best
at
> > steady 50mph, or even 45mph, if it's a particularly unaerodynamic with
roof
> > rails.
> >
> > Christian.
>
>
> Aerodynamic resistance grows with the speed squared. So everything being
> equal, 50mph is more economical than 60mph is more economical than 70mph
> and so on. But the efficiency also depends on the rpm, hence having a good
> gear ratio for the speed. My Saab has an instant mpg readout. (Why is it
> called readout and nor writeout?). I certainly find that my Saab is very
> economical at 50mph and that the consumption always increases (mpg
decreases)
> with speed, just as you would expect.

Aim for 52 mpg which is what I can get from a motorway trip at 60mph in my
1998 1.6 laguna (petrol).

Stu


"Johannes"  wrote in message
news:4326FE8F.52F7633A@spam-gets-slammed-sizefitter.com...

>
>
> Christian McArdle wrote:
> >
> > > For maximum economy what speed and/or RPM should I be looking to keep
at
> > on
> > > motorways? Am I right to assume I should chose motorway routes rather
than
> > > stop-start normal road routes?
> >
> > Modern aerodynamic cars are best at about a steady 60mph in top gear.
> > Anything more brick shaped will be optimum slower. A van might be best
at
> > steady 50mph, or even 45mph, if it's a particularly unaerodynamic with
roof
> > rails.
> >
> > Christian.
>
>
> Aerodynamic resistance grows with the speed squared. So everything being
> equal, 50mph is more economical than 60mph is more economical than 70mph
> and so on. But the efficiency also depends on the rpm, hence having a good
> gear ratio for the speed. My Saab has an instant mpg readout. (Why is it
> called readout and nor writeout?). I certainly find that my Saab is very
> economical at 50mph and that the consumption always increases (mpg
decreases)
> with speed, just as you would expect.

> Aerodynamic resistance grows with the speed squared. So everything being
> equal, 50mph is more economical than 60mph is more economical than 70mph
> and so on. But the efficiency also depends on the rpm, hence having a good
> gear ratio for the speed. My Saab has an instant mpg readout. (Why is it
> called readout and nor writeout?). I certainly find that my Saab is very
> economical at 50mph and that the consumption always increases (mpg
decreases)
> with speed, just as you would expect.


Yes, but there are other issues that don't vary with the square of speed.
Some elements are effectively constant with speed, such as lighting, audio
equipment, computer electrical consumption and air conditioning.

Fuel efficiency is actually a peaked curved, with the peak varying in speed,
but usually quite shallow from 45mph-60mph, there being little to pick
between. Above 70mph or below 40mph, efficiency drops off relatively
rapidly.

Obviously, every car will have a different peak, depending on many factors.
Just turning on the air con will raise your cars most efficient speed.

Christian.

Stuart Lyon wrote:

> 
> Aim for 52 mpg which is what I can get from a motorway trip at 60mph in my
> 1998 1.6 laguna (petrol).


I don't rely too much on the instant mpg readout in my car. Apart from
calibration, it also depends on the slope of the road and the wind speed
and direction. However, it is a useful tool for getting an idea of what
affects the fuel consumption, and to diagnose a possible problem.

"Christian McArdle"  wrote in message 
news:4326f4b1$0$12172$ed9e5944@reading.news.pipex.net...

>> For maximum economy what speed and/or RPM should I be looking to keep at
> on
>> motorways? Am I right to assume I should chose motorway routes rather 
>> than
>> stop-start normal road routes?
>
> Modern aerodynamic cars are best at about a steady 60mph in top gear.
> Anything more brick shaped will be optimum slower. A van might be best at
> steady 50mph, or even 45mph, if it's a particularly unaerodynamic with 
> roof
> rails.



Cobblers.  You may find that a certain car is more efficient (if efficiency 
is better) at 90 mph compared to 50 mph.  Or it'll be more economical at 44 
mph...

-- 
The DervMan
www.dervman.com

"Johannes"  wrote in message 
news:432702F2.4AE20469@spam-gets-slammed-sizefitter.com...

>
>
> Stuart Lyon wrote:
>>
>> Aim for 52 mpg which is what I can get from a motorway trip at 60mph in 
>> my
>> 1998 1.6 laguna (petrol).
>
> I don't rely too much on the instant mpg readout in my car. Apart from
> calibration, it also depends on the slope of the road and the wind speed
> and direction. However, it is a useful tool for getting an idea of what
> affects the fuel consumption, and to diagnose a possible problem.


As you'd expect then! :)

-- 
The DervMan
www.dervman.com

On Tue, 13 Sep 2005 09:00:54 GMT, Johannes
 wrote:

[snip]

> However, you can get away with 60mph by
>following Heavy Goods Vehicles that are restricted to 60mph anyway. 


And since you're following them, make sure you drive right up their
arse for the best slipstreaming. It'll probably annoy them, but that's
just a bonus.

'course, what's best for economy might not be best for safety ;o)

Cheers,

Colin.

"DervMan"  wrote in message
news:upEVe.7426$zw1.2533@newsfe2-gui.ntli.net...

> "Christian McArdle"  wrote in message
> news:4326f4b1$0$12172$ed9e5944@reading.news.pipex.net...
> >> For maximum economy what speed and/or RPM should I be looking to keep
at
> > on
> >> motorways? Am I right to assume I should chose motorway routes rather
> >> than
> >> stop-start normal road routes?
> >
> > Modern aerodynamic cars are best at about a steady 60mph in top gear.
> > Anything more brick shaped will be optimum slower. A van might be best
at
> > steady 50mph, or even 45mph, if it's a particularly unaerodynamic with
> > roof
> > rails.
>
>
> Cobblers.  You may find that a certain car is more efficient (if
efficiency
> is better) at 90 mph compared to 50 mph.  Or it'll be more economical at
44
> mph...


My Focus will do over 45 to the gallon at upto 75mph, any more than about 80
and that plummets rapidly.

Contrary, the S70 only averages about 31mpg at 65-70mph, but up that to
75-85 and it jumps to 35-36mpg.

Tim..

"Ben"  wrote in message
news:UroVe.24140$k22.4455@fe2.news.blueyonder.co.uk...

> Hi all,
>
> I've got a 1997 1.6 Nissan Almera with half a tank of petrol (let the
> bidding commence for the fuel LOL). I've got to do a few trips betwen
> Liverpool, St Helens and Bolton between now and the weekend for work
> purposes. I'm self employed and have to work to earn so can use the petrol
> situation as an excuse.
>
> For maximum economy what speed and/or RPM should I be looking to keep at
on
> motorways? Am I right to assume I should chose motorway routes rather than
> stop-start normal road routes?
>
> Thanks for your advice everybody :o)
>
> Ben
>
>

====================
If you're a glutton for punishment fit a vacuum gauge and try using that as
an 'economy gauge'.

Steady driving without trying to maintain a fixed speed is usually best for
economy - all other factors being equal!

Cic.

Tim.. wrote:



> Open windows increase drag by about 10%, so if you need to drive with one
> open, have it only down a jiffy.


But don't compensate by using aircon.
If your car's black, paint it white to stay cool.

>> Modern aerodynamic cars are best at about a steady 60mph in top gear.
>> Anything more brick shaped will be optimum slower. A van might be best at
>> steady 50mph, or even 45mph, if it's a particularly unaerodynamic with
>> roof rails.
>
> Cobblers.  You may find that a certain car is more efficient (if
efficiency
> is better) at 90 mph compared to 50 mph.  Or it'll be more economical at
44
> mph...


As I said, it depends on the car. However, as a general rule, modern, more
aerodynamic, and sporty cars generally have their most efficient speed at a
comparatively high speed.

It is very unlikely, however, that any normal road going car would be more
efficient at 90mph than 50mph, though, as the v squared really kicks in by
then. A specialist aerodynamic record breaking car would be required for
that.

Christian.

"Tim.."  wrote in message
news:dg79li$dha$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...

>
>
> My Focus will do over 45 to the gallon at upto 75mph, any more than about
80
> and that plummets rapidly.
>
> Contrary, the S70 only averages about 31mpg at 65-70mph, but up that to
> 75-85 and it jumps to 35-36mpg.


Uncannily I have access to both the same cars.

As to your S70 figures, is yours a manual or auto? I find that around 70 -
perhaps up to around 75 - I can average (according to the computer) easily
in the mid 30s - given a long enough run. However approaching 80, or higher,
and it drops off quite sharply.

In message <4327e5e9$0$12172$ed9e5944@reading.news.pipex.net>, Douglas 
Hall <?@?.?.invalid> writes

>"Tim.."  wrote in message
>news:dg79li$dha$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
>>
>>
>> My Focus will do over 45 to the gallon at upto 75mph, any more than about
>80
>> and that plummets rapidly.
>>
>> Contrary, the S70 only averages about 31mpg at 65-70mph, but up that to
>> 75-85 and it jumps to 35-36mpg.
>
>Uncannily I have access to both the same cars.
>
>As to your S70 figures, is yours a manual or auto? I find that around 70 -
>perhaps up to around 75 - I can average (according to the computer) easily
>in the mid 30s - given a long enough run. However approaching 80, or higher,
>and it drops off quite sharply.


I wonder how much influence traffic has on this; if you try to maintain 
a speed between that of the HGVs and the prevailing flow of the traffic, 
passing a lorry often involves easing off and waiting for a large enough 
gap in lane 2 not to impede passing traffic and then accelerating back 
to your cruising speed. If you're travelling at about the same speed as 
the muppets hogging the middle lane it's easier to find a gap in lane 2 
without having to lose and regain speed.

I suppose the other way of maintaining a constant speed is to be a 
lane-hogging muppet...

-- 
Steve Walker

"Steve Walker"  wrote in message
news:CD$j5wKCZ$JDFwvM@otolith.demon.co.uk...

>
> I wonder how much influence traffic has on this; if you try to maintain
> a speed between that of the HGVs and the prevailing flow of the traffic,
> passing a lorry often involves easing off and waiting for a large enough
> gap in lane 2 not to impede passing traffic and then accelerating back
> to your cruising speed. If you're travelling at about the same speed as
> the muppets hogging the middle lane it's easier to find a gap in lane 2
> without having to lose and regain speed.
>
> I suppose the other way of maintaining a constant speed is to be a
> lane-hogging muppet...


Actually, I've found it easier this week, ensuring that cruise is set to
dead-on 70 (which I know from experience gives me reasonably good fuel
economy), and perhaps the motorways have been a little lighter on traffic
due to the fuel scares. Plus I've been setting off a little earlier,
allowing more time for my journey. I've actually found it reasonably easy to
leave it on cruise, and so long as I've timed my moves to lane 2 well for
slower traffic, I've not had to slow that often - and the main times it has
happened, has been because of lane 2 traffic, slowing to the same similar as
my speed just as they pass / draw alongside.

I find driving at a constant speed just requires more planning for lane
changes - but doesn't necessarily dictate lane-hogging.

In message <43280305$0$12181$ed9e5944@reading.news.pipex.net>, Douglas 
Hall <?@?.?.invalid> writes

>"Steve Walker"  wrote in message
>news:CD$j5wKCZ$JDFwvM@otolith.demon.co.uk...
>>
>> I wonder how much influence traffic has on this; if you try to maintain
>> a speed between that of the HGVs and the prevailing flow of the traffic,
>> passing a lorry often involves easing off and waiting for a large enough
>> gap in lane 2 not to impede passing traffic and then accelerating back
>> to your cruising speed. If you're travelling at about the same speed as
>> the muppets hogging the middle lane it's easier to find a gap in lane 2
>> without having to lose and regain speed.
>>
>> I suppose the other way of maintaining a constant speed is to be a
>> lane-hogging muppet...
>
>Actually, I've found it easier this week, ensuring that cruise is set to
>dead-on 70 (which I know from experience gives me reasonably good fuel
>economy), and perhaps the motorways have been a little lighter on traffic
>due to the fuel scares.


And slower, I'm guessing. They were last time people were worried about 
fuel shortages, and I've noticed the traffic on the dual carriageway is 
going at 60-70 mph instead of the usual 70-90. Much more bunching of 
traffic, too.


>I've actually found it reasonably easy to
>leave it on cruise, and so long as I've timed my moves to lane 2 well for
>slower traffic, I've not had to slow that often - and the main times it has
>happened, has been because of lane 2 traffic, slowing to the same similar as
>my speed just as they pass / draw alongside.


That happens. It's depends on the speed differential. I found that doing 
about 70 in the Citroen AX we had gave better economy than doing about 
60, but I reckon that would not have been the case on an empty motorway 
and that I'd have got better still if I'd just slowed to the speed of 
the HGVs. Life's too short.


>I find driving at a constant speed just requires more planning for lane
>changes - but doesn't necessarily dictate lane-hogging.


Of course not, but until I'm prime minister and implement my plan 
involving helicopters and air-to-ground missiles, it's how a lot of 
people do it.

-- 
Steve Walker

"Willy Eckerslyke"  wrote in message
news:dg8kr6$d31$1@fantastix.bangor.ac.uk...

> Tim.. wrote:
>
>
> > Open windows increase drag by about 10%, so if you need to drive with
one
> > open, have it only down a jiffy.
>
> But don't compensate by using aircon.
> If your car's black, paint it white to stay cool.


Actually using the a/c uses less fuel than running with the windows down.

Tim..

"Douglas Hall" <@> wrote in message
news:4327e5e9$0$12172$ed9e5944@reading.news.pipex.net...

> "Tim.."  wrote in message
> news:dg79li$dha$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
> >
> >
> > My Focus will do over 45 to the gallon at upto 75mph, any more than
about
> 80
> > and that plummets rapidly.
> >
> > Contrary, the S70 only averages about 31mpg at 65-70mph, but up that to
> > 75-85 and it jumps to 35-36mpg.
>
> Uncannily I have access to both the same cars.
>
> As to your S70 figures, is yours a manual or auto? I find that around 70 -
> perhaps up to around 75 - I can average (according to the computer) easily
> in the mid 30s - given a long enough run. However approaching 80, or
higher,
> and it drops off quite sharply.


Manual.

Using the instant readout and driving at different speeds, it shows that
between 2500-3000rpm mpg is lower than when over 3000rpm. This is in 5th
gear.

I have not experimented with 4th gear at the same speed to keep the revs to
3000rpm or more yet.

I am reasoning is that torque output below 3k is low and the engine is
effectivly labouring with a wider throttle opening than that at a higher
roadspeed.

I would add its the 2.5 10v engine which does about 27mph / 1000rpm in 5th.
(100mph indicated= 3600rpm)

Tim..

"Douglas Hall" <@> wrote in message
news:4327e5e9$0$12172$ed9e5944@reading.news.pipex.net...

> "Tim.."  wrote in message
> news:dg79li$dha$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
> >
> >
> > My Focus will do over 45 to the gallon at upto 75mph, any more than
about
> 80
> > and that plummets rapidly.
> >
> > Contrary, the S70 only averages about 31mpg at 65-70mph, but up that to
> > 75-85 and it jumps to 35-36mpg.
>
> Uncannily I have access to both the same cars.
>
> As to your S70 figures, is yours a manual or auto? I find that around 70 -
> perhaps up to around 75 - I can average (according to the computer) easily
> in the mid 30s - given a long enough run. However approaching 80, or
higher,
> and it drops off quite sharply.


PS this is with the cruise control on maintaining a constant speed.

Tim..

Tim.. wrote:


> Actually using the a/c uses less fuel than running with the windows down.


Tiny bit of a generalisation there Tim. At some speeds in certain cars 
with the windows down to a certain level, I'll concede you may be right, 
depending on the level of cooling required, etc...

"Steve Walker"  wrote in message
news:orcpDsRDEBKDFwxa@otolith.demon.co.uk...

> In message <43280305$0$12181$ed9e5944@reading.news.pipex.net>, Douglas
> Hall <?@?.?.invalid> writes
> >"Steve Walker"  wrote in message
> >news:CD$j5wKCZ$JDFwvM@otolith.demon.co.uk...
> >>
> >> I suppose the other way of maintaining a constant speed is to be a
> >> lane-hogging muppet...
> >
> >Actually, I've found it easier this week, ensuring that cruise is set to
> >dead-on 70 (which I know from experience gives me reasonably good fuel
> >economy), and perhaps the motorways have been a little lighter on traffic
> >due to the fuel scares.
>
> And slower, I'm guessing. They were last time people were worried about
> fuel shortages, and I've noticed the traffic on the dual carriageway is
> going at 60-70 mph instead of the usual 70-90. Much more bunching of
> traffic, too.


On the motorway, it seems like traffic is generally slower - but as I'm
personally going slower, it may be deceptive - but quite a bit lighter. I
haven't personally seen bunching.

It's a funny thing, too - I've previously noted (using cruise control on the
motorway) that certain speeds could be more difficult for general traffic
(ie not particularly heavy) than others. That's just really a finger in the
air thing, really, but how it seemed to be if I had cruise set to an
indicated 73. At an indicated 70, it seems fairly easy to deal with slower
traffic, and changing lanes.


> >I've actually found it reasonably easy to
> >leave it on cruise, and so long as I've timed my moves to lane 2 well for
> >slower traffic, I've not had to slow that often - and the main times it
has
> >happened, has been because of lane 2 traffic, slowing to the same similar
as
> >my speed just as they pass / draw alongside.
>
> That happens. It's depends on the speed differential.


Not sure what you mean there? I've found numerous times over the past 3
days, that I can be doing an indicated 70 in lane 1, be slowly approaching
some traffic, have a car in lane 2 approaching to pass me, and everything
would be just fine, if they continued at their current pace, but once
alongside me slow to my speed for no apparent reason (ie nothing in their
lane ahead of them to cause it).

If I was paranoid, I'd almost think they did it on purpose, but I'm thinking
Occam's razor applies - either that or never ascribe to malice what could be
explained by incompetence - the instances when it's happened, I don't think
have been any particular intent to block me in. I'm just generally puzzled
as to why people do it.


> I found that doing
> about 70 in the Citroen AX we had gave better economy than doing about
> 60, but I reckon that would not have been the case on an empty motorway
> and that I'd have got better still if I'd just slowed to the speed of
> the HGVs. Life's too short.


Indeed. At the moment, trying to get the best compromise between fuel
economy and getting where I want to be in reasonable time, I figure 70 is
just fine.


> >I find driving at a constant speed just requires more planning for lane
> >changes - but doesn't necessarily dictate lane-hogging.
>
> Of course not,


I think I just wanted to make the point that there is something between
either having to constantly ease off, or disengage cruise and hog lanes.


> but until I'm prime minister and implement my plan
> involving helicopters and air-to-ground missiles, it's how a lot of
> people do it.


Quite - a lot do - and blissfully unaware (it would seem) of the
inconvenience to approaching faster traffic. MLOC and OLOC should be picked
off with missiles, or rounded up, sent to a deserted island where there's
all sorts of supernatural goings in, and their petrol distributed to those
people they've inconvenienced. Justice!

"Tim.."  wrote in message
news:dg95el$stl$1@nwrdmz01.dmz.ncs.ea.ibs-infra.bt.com...

>
> "Douglas Hall" <@> wrote in message
> news:4327e5e9$0$12172$ed9e5944@reading.news.pipex.net...
> > "Tim.."  wrote in message
> > news:dg79li$dha$1@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
> > >
> > >
> > > My Focus will do over 45 to the gallon at upto 75mph, any more than
> about
> > 80
> > > and that plummets rapidly.
> > >
> > > Contrary, the S70 only averages about 31mpg at 65-70mph, but up that
to
> > > 75-85 and it jumps to 35-36mpg.
> >
> > Uncannily I have access to both the same cars.
> >
> > As to your S70 figures, is yours a manual or auto? I find that around
70 -
> > perhaps up to around 75 - I can average (according to the computer)
easily
> > in the mid 30s - given a long enough run. However approaching 80, or
> higher,
> > and it drops off quite sharply.
>
> Manual.
>
> Using the instant readout and driving at different speeds, it shows that
> between 2500-3000rpm mpg is lower than when over 3000rpm. This is in 5th
> gear.


Mine is an auto - and I find the opposite, really. 70 indicated is around
2600rpm. 80 and above is 3000+.

I get much better averages, according to the computer at least, by sticking
under 80, and better the closer I am to 70. Haven't experimented for below
70 - I still want to make some progress :-)


> I have not experimented with 4th gear at the same speed to keep the revs
to
> 3000rpm or more yet.
>
> I am reasoning is that torque output below 3k is low and the engine is
> effectivly labouring with a wider throttle opening than that at a higher
> roadspeed.
>
> I would add its the 2.5 10v engine which does about 27mph / 1000rpm in
5th.
> (100mph indicated= 3600rpm)


Same engine for me.

I can't remember on the speeds per 1k revs in top, but 70 is around 2600rpm,
80 is 3000+, and as I mentioned above, it would appear for me keeping it
below 3k revs gives me the best fuel economy. I'd say the best fuel economy
I've got by maintaining constant speeds via cruise control, and on
reasonable distances on the motorway have been around an indicated 73, or
most recently at 70.

"Willy Eckerslyke"  wrote in message
news:dg9677$leh$1@fantastix.bangor.ac.uk...

> Tim.. wrote:
>
> > Actually using the a/c uses less fuel than running with the windows
down.
>
> Tiny bit of a generalisation there Tim. At some speeds in certain cars
> with the windows down to a certain level, I'll concede you may be right,
> depending on the level of cooling required, etc...


On the motorway, though, at normal motorway speeds, it's more likely that
the window being down rather than using the aircon is likely to introduce
more drag aerodynamically, than the compressor on the engine - unless the
engine is particularly weedy.

Douglas Hall wrote:


> On the motorway, though, at normal motorway speeds, it's more likely that
> the window being down rather than using the aircon is likely to introduce
> more drag aerodynamically, than the compressor on the engine - unless the
> engine is particularly weedy.


But why would anyone need aircon at motorway speeds? Why not just use 
the internal vents?

OK, I can see this may not be sufficient in some black cars on a really 
hot day, but anyone stupid enough to buy a car that colour can stew, IMO.

Willy Eckerslyke wrote:

> 
> Douglas Hall wrote:
> 
> > On the motorway, though, at normal motorway speeds, it's more likely that
> > the window being down rather than using the aircon is likely to introduce
> > more drag aerodynamically, than the compressor on the engine - unless the
> > engine is particularly weedy.
> 
> But why would anyone need aircon at motorway speeds? Why not just use
> the internal vents?
> 
> OK, I can see this may not be sufficient in some black cars on a really
> hot day, but anyone stupid enough to buy a car that colour can stew, IMO.


Even worse are those colours that are almost black, but not quite. It may
be some kind of metallic black. Hence very difficult to repair scratches.

"Willy Eckerslyke"  wrote in message
news:dg991c$mlg$1@fantastix.bangor.ac.uk...

> Douglas Hall wrote:
>
> > On the motorway, though, at normal motorway speeds, it's more likely
that
> > the window being down rather than using the aircon is likely to
introduce
> > more drag aerodynamically, than the compressor on the engine - unless
the
> > engine is particularly weedy.
>
> But why would anyone need aircon at motorway speeds? Why not just use
> the internal vents?


Simple, when the temperature of the air coming through the vents is still
warmer than you want.

On some of the warmer days, I'll be using the A/C whilst I'm on the
motorway. Typically, I find, when the outside temperature is over 23C I'll
be using it a bit. 25C and above, maybe quite a lot. 28C and probably
constantly.

Now I'll buy that the 25C+ days are dwindling, now, but most days when
driving home it's low twenties, and I'll use it a bit.

Douglas Hall wrote:


> "Willy Eckerslyke"  wrote in message
> news:dg991c$mlg$1@fantastix.bangor.ac.uk...

>>But why would anyone need aircon at motorway speeds? Why not just use
>>the internal vents?

> Simple, when the temperature of the air coming through the vents is still
> warmer than you want.


I said 'need'.

>> Simple, when the temperature of the air coming through the vents is still
>> warmer than you want.
>
> I said 'need'.


Well, no-one needs to drive a car, or even live, where do you want to stop?

Christian.

"Willy Eckerslyke"  wrote in message
news:dg9egb$p7o$1@fantastix.bangor.ac.uk...

> Douglas Hall wrote:
>
> > "Willy Eckerslyke"  wrote in message
> > news:dg991c$mlg$1@fantastix.bangor.ac.uk...
>
> >>But why would anyone need aircon at motorway speeds? Why not just use
> >>the internal vents?
>
> > Simple, when the temperature of the air coming through the vents is
still
> > warmer than you want.
>
> I said 'need'.


In which case, there's likely no true _need_ for cooling air through the
vents, either. Nor to be able to listen to the radio and / or music. And
clearly, the best fuel economy is likely to be achieved with as little
electronic or mechanical accessories being used - either in terms of
alternator drag, mechanical drag through auxiliary drive belts, or
aerodynamic drag.

However, the context of the discussion was regarding cooling - and likely
whilst at motorway speeds. And if somebody _wants_ the interior to be cooler
than it is (perhaps due to ambient, perhaps due to solar effects) then they
have numerous choices. Airflow through the vents - either by merit of road
speed, or by the fans, may not cut it. And at motorway speeds, aircon is
probably going to be more favourable compared with opening a window, in
terms of fuel economy.

But as you rightly imply, drivers most likely won't die or be injured by
such heat. The may likely just be a bit hot under the collar, or sweat a
lot - kudos for stressing the importance of your choice in words in using
"need".

However, if somebody wasn't sure which option would be preferable in terms
of fuel economy - and given the context of the OP post, that seems a
reasonable proposition - I see nothing wrong in informing them.

Christian McArdle wrote:


>>>Simple, when the temperature of the air coming through the vents is still
>>>warmer than you want.
>>
>>I said 'need'.
> 
> Well, no-one needs to drive a car, or even live, where do you want to stop?


Well the subject is 'economic driving' so I assumed the OP wanted the 
best mpg he could reasonably hope for. Driving without aircon in the UK 
is hardly a big deal, IMO, but then I'm not some soft southern pooftah 
who can't function outside of a micro-controlled environment.

Douglas Hall wrote:


> In which case, there's likely no true _need_ for cooling air through the
> vents, either. Nor to be able to listen to the radio and / or music. And
> clearly, the best fuel economy is likely to be achieved with as little
> electronic or mechanical accessories being used - either in terms of
> alternator drag, mechanical drag through auxiliary drive belts, or
> aerodynamic drag.


Have you been looking in my garage?

> Well the subject is 'economic driving' so I assumed the OP wanted the
> best mpg he could reasonably hope for. Driving without aircon in the UK
> is hardly a big deal, IMO, but then I'm not some soft southern pooftah
> who can't function outside of a micro-controlled environment.


I'm may be some soft southern pooftah, but I don't even have aircon! When I
had a car that did, I did use it quite a lot, though, even when it wasn't
that hot. The dehumidifying was very comfortable.

Christian.

In article <43280305$0$12181$ed9e5944@reading.news.pipex.net>, "Douglas 
Hall" <@> says...

> "Steve Walker"  wrote in message
> news:CD$j5wKCZ$JDFwvM@otolith.demon.co.uk...
> >
> > I wonder how much influence traffic has on this; if you try to maintain
> > a speed between that of the HGVs and the prevailing flow of the traffic,
> > passing a lorry often involves easing off and waiting for a large enough
> > gap in lane 2 not to impede passing traffic and then accelerating back
> > to your cruising speed. If you're travelling at about the same speed as
> > the muppets hogging the middle lane it's easier to find a gap in lane 2
> > without having to lose and regain speed.
> >
> > I suppose the other way of maintaining a constant speed is to be a
> > lane-hogging muppet...
> 
> Actually, I've found it easier this week, ensuring that cruise is set to
> dead-on 70 (which I know from experience gives me reasonably good fuel
> economy), and perhaps the motorways have been a little lighter on traffic
> due to the fuel scares. 


I've certainly seen more cars doing dead on 70, and not the ones you'd 
normally see, Audi, VW etc.

The White Van Men are still driving like total muppets as usual.


> I've actually found it reasonably easy to
> leave it on cruise, and so long as I've timed my moves to lane 2 well for
> slower traffic, I've not had to slow that often - and the main times it has
> happened, has been because of lane 2 traffic, slowing to the same similar as
> my speed just as they pass / draw alongside.
> 
> I find driving at a constant speed just requires more planning for lane
> changes - but doesn't necessarily dictate lane-hogging.


I'm doing the same this week. Partly due to uncertainty about fuel, and 
partly to see what I can do.

Over 2 days, I've now averaged >60mph, which I'm pretty impressed at. THis 
is where I find cruise handy. It's a little lighter with its right foot 
than I am!

Pete.

-- 
NOTE! Email address is spamtrapped. Any email will be deleted
Remove the news and underscore from my address to reply by mail

It was somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Colin Stamp
 saying something like:


>>following Heavy Goods Vehicles that are restricted to 60mph anyway. 
>
>And since you're following them, make sure you drive right up their
>arse for the best slipstreaming. It'll probably annoy them, but that's
>just a bonus.
>
>'course, what's best for economy might not be best for safety ;o)


There's a secondary region of calm air behind a truck, Some 40 t0 60
feet behind it, the airflow has curled round the back of the truck and
calmed down again, seeming to leave a slightly low pressure area. This
works for box-bodied rigids and most trailer units travelling at 60mph.

 Try it on a bike; you really feel it. I first discovered this when I
was on the motorways during my first biking winter on a slow old
shitheap and didn't have a decent fairing or proper bike gear. That calm
air region made a 400mile journey in February bearable.

The point I'm making though, is that same calm(er) air region can help
you slipstream without incurring the interest of the dibbles.
-- 

Dave
SE6a

"Willy Eckerslyke"  wrote in message
news:dg9hkt$qud$1@fantastix.bangor.ac.uk...

> Christian McArdle wrote:
>
> >>>Simple, when the temperature of the air coming through the vents is
still
> >>>warmer than you want.
> >>
> >>I said 'need'.
> >
> > Well, no-one needs to drive a car, or even live, where do you want to
stop?
>
> Well the subject is 'economic driving' so I assumed the OP wanted the
> best mpg he could reasonably hope for.


In which case, he'd probably attempt to ascertain which particular speed is
likely to produce the best mpg - but like many things, life, she is a
compromise.

As an example, this week - as well as being aware that there may be petrol
shortages, I've tried to get the best fuel economy I can _within reason_ I
still want to make reasonable progress, and I still want a pleasant
environment in the car.

And if somebody wants to be cooled in the car, at motorway speeds, _if_ the
options are opening the window, or using aircon, then for that scenario,
aircon is probably the better one.

If somebody simply wants the best fuel economy from their car, over a given
distance, they'd drive at the most fuel efficient speed, as much as
possible, and only have the bare essentials of electrical equipment on (ie
wipers, if need be, headlights where required, fans and heated screens
merely to maintain clear windows).


> Driving without aircon in the UK
> is hardly a big deal, IMO,


Fine. Feel free not to use it, or buy a car with it. I personally wouldn't
be without it, these days - nor would my wife ;-)

I suspect I'm not alone in that.


> but then I'm not some soft southern pooftah
> who can't function outside of a micro-controlled environment.


Kudos. Your self-esteem must be off the scale.

"Willy Eckerslyke"  wrote in message
news:dg9i5n$r6e$1@fantastix.bangor.ac.uk...

> Douglas Hall wrote:
>
> > In which case, there's likely no true _need_ for cooling air through the
> > vents, either. Nor to be able to listen to the radio and / or music. And
> > clearly, the best fuel economy is likely to be achieved with as little
> > electronic or mechanical accessories being used - either in terms of
> > alternator drag, mechanical drag through auxiliary drive belts, or
> > aerodynamic drag.
>
> Have you been looking in my garage?


I thought I'd keep quiet about it acksherly.

Of course, it would be folly to think the entire motoring public has quite
the same priorities as either you, or I.

Douglas Hall wrote:


> Of course, it would be folly to think the entire motoring public has quite
> the same priorities as either you, or I.


You've hit the nail on the head there. While I wouldn't expect many 
people to put up with the lack of creature comforts I enjoy (Hell, one 
of my cars doesn't even have any venting from the outside apart from the 
windows), I do despair at what's seen as essential by so many these days.
If this fuel scare encourages people to reassess their priorities even a 
little, then it may be no bad thing.

Grumpy old man, me?
Never!

"Willy Eckerslyke"  wrote in message
news:dgbcfl$nk9$1@fantastix.bangor.ac.uk...

> Douglas Hall wrote:
>
> > Of course, it would be folly to think the entire motoring public has
quite
> > the same priorities as either you, or I.
>
> You've hit the nail on the head there. While I wouldn't expect many
> people to put up with the lack of creature comforts I enjoy (Hell, one
> of my cars doesn't even have any venting from the outside apart from the
> windows), I do despair at what's seen as essential by so many these days.


Well each to their own. Personally, I spend 2-3 hours a day in my car on a
weekday. So having some creature comforts and a pleasant environment is
important to me.


> If this fuel scare encourages people to reassess their priorities even a
> little, then it may be no bad thing.


Well it has for me, in the past week - in that I do a fair number of miles,
and the prospect that there may be issues filling-up, plus the cost of this
motoring has made me consider what's within my control in keeping the cost
of fuel usage down. However, I wouldn't give up air-con if I felt I wanted
it on. In the same way, I see a balance between making reasonable progress,
and keeping the speed within bounds that are reasonable in terms of
consumption.


> Grumpy old man, me?
> Never!


;-)

"Willy Eckerslyke"  wrote in message 
news:dg9677$leh$1@fantastix.bangor.ac.uk...

> Tim.. wrote:
>
>> Actually using the a/c uses less fuel than running with the windows down.
>
> Tiny bit of a generalisation there Tim. At some speeds in certain cars 
> with the windows down to a certain level, I'll concede you may be right, 
> depending on the level of cooling required, etc...


Consider this.  The air conditioning compressor cycles in and out.  Opening 
a window keeps it open.

For our Ka on the motorway, the additional loading caused by the compressor 
is around 10%.  Using the window is around 6%.  The compressor is typically 
engaged around 50% of the time when ambient air temperature is between 25 
and 27 degrees and the speedometer is between 55 and 70.

Advantage: air conditioning.

Then there's noise and temperature.

Double advantage air conditioning.


-- 
The DervMan
www.dervman.com

"Christian McArdle"  wrote in message 
news:4327e381$0$12180$ed9e5944@reading.news.pipex.net...

>>> Modern aerodynamic cars are best at about a steady 60mph in top gear.
>>> Anything more brick shaped will be optimum slower. A van might be best 
>>> at
>>> steady 50mph, or even 45mph, if it's a particularly unaerodynamic with
>>> roof rails.
>>
>> Cobblers.  You may find that a certain car is more efficient (if
> efficiency
>> is better) at 90 mph compared to 50 mph.  Or it'll be more economical at
> 44
>> mph...
>
> As I said, it depends on the car. However, as a general rule, modern, more
> aerodynamic, and sporty cars generally have their most efficient speed at 
> a
> comparatively high speed.
>
> It is very unlikely, however, that any normal road going car would be more
> efficient at 90mph than 50mph, though, as the v squared really kicks in by
> then. A specialist aerodynamic record breaking car would be required for
> that.



I'll wager that the M5 is more efficient at 90 compared to 50.

-- 
The DervMan
www.dervman.com