My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Air conditioning compressor? Electric fan constantly on trying to keep
the engine cool?
On 2025-07-13 13:33, alan_m wrote:
On 13/07/2025 12:54, Scott wrote:I should think 63.5 mpg is fairly normal for a modern car driven in
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Air conditioning compressor? Electric fan constantly on trying to keep
the engine cool?
almost optimum conditions. I don't have to try very hard to beat 60 with
our hybrid on a long non-motorway journey.
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Air conditioning compressor? Electric fan constantly on trying to keep
the engine cool?
On Sun, 13 Jul 2025 13:33:05 +0100, alan_m <junk@admac.myzen.co.uk>
wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Air conditioning compressor? Electric fan constantly on trying to keep
the engine cool?
The air conditioning was checked last week and is booked in for a new condenser on Tuesday. I assume the compressor is okay but I will
certainly ask. The fan is an interesting thought and would explain the
lack of any correlation with steering. Is there an easy way to check?
On 2025-07-13 13:33, alan_m wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Air conditioning compressor? Electric fan constantly on trying to
keep the engine cool?
I should think 63.5 mpg is fairly normal for a modern car driven in
almost optimum conditions. I don't have to try very hard to beat 60 with
our hybrid on a long non-motorway journey.
nib
On 2025-07-13 13:33, alan_m wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I should think 63.5 mpg is fairly normal for a modern car driven in63.5 mpg for a *petrol* car seems exceptionally good. What sort of
almost optimum conditions. I don't have to try very hard to beat 60 with
our hybrid on a long non-motorway journey.
On 13/07/2025 14:15, nib wrote:
On 2025-07-13 13:33, alan_m wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
[snip]
I should think 63.5 mpg is fairly normal for a modern car driven in63.5 mpg for a *petrol* car seems exceptionally good. What sort of consumption were you typically getting before the journey you refer to?
almost optimum conditions. I don't have to try very hard to beat 60
with our hybrid on a long non-motorway journey.
I have a 2008 Peugeot 308 1.6 HDi (diesel). I tend to accelerate
moderately briskly but never tyre-shreddingly! I rarely exceed 70 on a motorway, though I tend always to drive at or slightly below the speed
limit if it's safe to do so (as opposed to choosing to drive much slower
than the limit). I also anticipate in good time so I come off the power
when I see that I will need to slow down, rather than remaining under
power and then braking harder later.
My car has averaged about 55 mpg over its whole 200,000 mile life so
far. I tend to get full-tank to full-tank averages (fuel bought to fill
to pump-shutoff divided by distance since last filling) of about 45-55
mpg. There will be some variation in when a given pump shuts off. When I
was doing a lot of longer journeys on motorways and fast single/dual- carriageways (ie not with much around-town driving) I was averaging
around 57 mpg. The best ever tank-to-tank figure was about 63.5.
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car?
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Did the noise also occur with the car statioary but with the engine
running? If so, you can eliminate anything transmission-related.
As a matter of interst, how did you measure MPG?
On 13/07/2025 14:15, nib wrote:
On 2025-07-13 13:33, alan_m wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
[snip]
I should think 63.5 mpg is fairly normal for a modern car driven in63.5 mpg for a *petrol* car seems exceptionally good. What sort of consumption were you typically getting before the journey you refer to?
almost optimum conditions. I don't have to try very hard to beat 60
with our hybrid on a long non-motorway journey.
I have a 2008 Peugeot 308 1.6 HDi (diesel). I tend to accelerate
moderately briskly but never tyre-shreddingly! I rarely exceed 70 on a motorway, though I tend always to drive at or slightly below the speed
limit if it's safe to do so (as opposed to choosing to drive much slower
than the limit). I also anticipate in good time so I come off the power
when I see that I will need to slow down, rather than remaining under
power and then braking harder later.
My car has averaged about 55 mpg over its whole 200,000 mile life so
far. I tend to get full-tank to full-tank averages (fuel bought to fill
to pump-shutoff divided by distance since last filling) of about 45-55
mpg. There will be some variation in when a given pump shuts off. When I
was doing a lot of longer journeys on motorways and fast single/dual-carriageways (ie not with much around-town driving) I was averaging around 57 mpg. The best ever tank-to-tank figure was about 63.5.
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
I accidentally put some petrol in my Fiat Panda diesel. .....
... Didn't seem to do it any long-term harm, it was still going last I heard (gave
it to a family member when it got old).
A diversion from that. I believe (anyway it's my guess) that many modern
cars measure the fuel consumption for the trip computer by summing the durations of the injector timings, thus making it very cheap (just
software) to add this function.
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
Did the noise also occur with the car statioary but with the engine
running? If so, you can eliminate anything transmission-related.
As a matter of interst, how did you measure MPG?
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car?
Was that the car's reported reading or yours based on odometer miles >travelled divided by gallons (litres) from the petrol pump?
Jeff Layman wrote:
In that case, the car is only doing around 45 mph when the speedo shows
50. It's probably just Honda being ultracautious in that they could
never be held responsible for a faulty speedo contributing to a speeding >>offence taking place.
It is in Construction & Rules - there is no positive tolerance,
so, unless the speedo hardware is unusually accurate, it will
always read low.
On Sun, 13 Jul 2025 18:42:25 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car?
Was that the car's reported reading or yours based on odometer miles
travelled divided by gallons (litres) from the petrol pump?
The first of these. As a piece of history, I believe the Nissan Micra
was the only car ever to exceed its declared mpg figure in Honest
John's website. I think it got 101%.
In that case, the car is only doing around 45 mph when the speedo shows
50. It's probably just Honda being ultracautious in that they could
never be held responsible for a faulty speedo contributing to a speeding >offence taking place.
On Mon, 14 Jul 2025 11:47:16 +0100, Chris J Dixon <chris@cdixon.me.uk>
wrote:
Jeff Layman wrote:
In that case, the car is only doing around 45 mph when the speedo shows >>50. It's probably just Honda being ultracautious in that they could
never be held responsible for a faulty speedo contributing to a speeding >>offence taking place.
It is in Construction & Rules - there is no positive tolerance,
so, unless the speedo hardware is unusually accurate, it will
always read low.
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Scott <newsgroups@gefion.myzen.co.uk> wrote:
On Mon, 14 Jul 2025 11:47:16 +0100, Chris J Dixon <chris@cdixon.me.uk>
wrote:
Jeff Layman wrote:Read high, surely? Otherwise customers driving at the speed limit
In that case, the car is only doing around 45 mph when the speedo shows
50. It's probably just Honda being ultracautious in that they could
never be held responsible for a faulty speedo contributing to a speeding >> >>offence taking place.
It is in Construction & Rules - there is no positive tolerance,
so, unless the speedo hardware is unusually accurate, it will
always read low.
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it >actually knows the accurate speed and just chooses to inflate it 10% for the >speedo display.
I assume the odometer is measured using the real speed and not the inflated >value, so that the car at 100,000 miles hasn't actually done only 91,000.
On Mon, 14 Jul 2025 11:47:16 +0100, Chris J Dixon <chris@cdixon.me.uk>
wrote:
Jeff Layman wrote:Read high, surely? Otherwise customers driving at the speed limit
In that case, the car is only doing around 45 mph when the speedo shows >>>50. It's probably just Honda being ultracautious in that they could
never be held responsible for a faulty speedo contributing to a speeding >>>offence taking place.
It is in Construction & Rules - there is no positive tolerance,
so, unless the speedo hardware is unusually accurate, it will
always read low.
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it actually knows the accurate speed and just chooses to inflate it 10% for the speedo display.
I assume the odometer is measured using the real speed and not the inflated value, so that the car at 100,000 miles hasn't actually done only 91,000.
I assume the odometer is measured using the real speed and not the inflated value, so that the car at 100,000 miles hasn't actually done only 91,000.
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car?
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10% for the >> speedo display.
Does it have some GPS to know the accurate speed? If it is relying on wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the inflated >> value, so that the car at 100,000 miles hasn't actually done only 91,000.
Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
  Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
  Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
On Sun, 13 Jul 2025 17:27:17 -0000 (UTC), RJH <patchmoney@gmx.com>
wrote:
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
As OP, I think NY was referring to my car achieving 63.5 mpg. My car I
can assure you is a 2008 Micra and categorically not a hybrid of any
form.
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
  Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
On 14/07/2025 09:19, Scott wrote:
On Sun, 13 Jul 2025 17:27:17 -0000 (UTC), RJH <patchmoney@gmx.com>
wrote:
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
As OP, I think NY was referring to my car achieving 63.5 mpg. My car I
can assure you is a 2008 Micra and categorically not a hybrid of any
form.
Yes I was.
I still don't understand how PHEVs can be more efficient that pure
petrols because the energy to recharge the battery for the bursts of acceleration in between the low-power cruising still has to come from somewhere - the petrol.
On 14/07/2025 09:19, Scott wrote:
On Sun, 13 Jul 2025 17:27:17 -0000 (UTC), RJH <patchmoney@gmx.com>
wrote:
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
As OP, I think NY was referring to my car achieving 63.5 mpg. My car I
can assure you is a 2008 Micra and categorically not a hybrid of any
form.
Yes I was.
I still don't understand how PHEVs can be more efficient that pure
petrols because the energy to recharge the battery for the bursts of acceleration in between the low-power cruising still has to come from somewhere - the petrol.
On 13/07/2025 19:50, nib wrote:
A diversion from that. I believe (anyway it's my guess) that many
modern cars measure the fuel consumption for the trip computer by
summing the durations of the injector timings, thus making it very
cheap (just software) to add this function.
On my Ford Focus you can display the near real time figure for miles/gal
on the dash. One thing I noticed is with a very light foot and going
downhill the display tops out at 99.9 miles/gal.  I have no idea if
this is just the software limiting the displayed data of if the actual calculation has some limitation when little fuel is being used.
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it actually knows the accurate speed and just chooses to inflate it 10% for the
speedo display.
Does it have some GPS to know the accurate speed? If it is relying on
wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the inflated value, so that the car at 100,000 miles hasn't actually done only 91,000.
Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
NY <me@privacy.net> wrote:
On 14/07/2025 09:19, Scott wrote:
On Sun, 13 Jul 2025 17:27:17 -0000 (UTC), RJH <patchmoney@gmx.com>
wrote:
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-) >>>>The point is, though, that it's not a petrol car - it's a PHEV.
As OP, I think NY was referring to my car achieving 63.5 mpg. My car I
can assure you is a 2008 Micra and categorically not a hybrid of any
form.
Yes I was.
I still don't understand how PHEVs can be more efficient that pure
petrols because the energy to recharge the battery for the bursts of
acceleration in between the low-power cruising still has to come from
somewhere - the petrol.
They get it from wall charging the battery.
(PHEV = plugin hybrid)
The EV part is ~90% efficient, the petrol part is ~40% efficient, so you get some mix of efficiency depending on your usage.
Non-plugin hybrids have a more efficient drivetrain than a traditional
petrol because they run the engine at its most efficient part of the cycle and recover energy from regenerative braking. They also allow the engine to be smaller because acceleration partially comes from the battery, rather
than fitting a thirsty big engine just for peak acceleration.
Theo
On 14/07/2025 17:21, Jeff Layman wrote:
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
Does it have some GPS to know the accurate speed? If it is relying on >> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already showing!
I use GPS and the radar signs that clock your speed in 30 limits
They all agree. 33mph indicated is 30mph actual.
At 40 mph, its 44. at 50 its also 54. At 60 its 65.
I set the cruise control accordingly.
--
I
On 13/07/2025 19:50, nib wrote:
A diversion from that. I believe (anyway it's my guess) that many modern
cars measure the fuel consumption for the trip computer by summing the
durations of the injector timings, thus making it very cheap (just
software) to add this function.
On my Ford Focus you can display the near real time figure for miles/gal
on the dash. One thing I noticed is with a very light foot and going
downhill the display tops out at 99.9 miles/gal. I have no idea if
this is just the software limiting the displayed data of if the actual calculation has some limitation when little fuel is being used.
I use GPS and
the radar signs that clock your speed in 30 limits
On 2025-07-14 17:21, Jeff Layman wrote:
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it >>>> actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >>> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
  Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four
markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
The little marker posts are 100 metres apart, so you time 16 intervals,
which is a mile to within about 0.5%.
nib
On 14/07/2025 17:21, Jeff Layman wrote:
On 14/07/2025 13:59, Nick Finnigan wrote:I use GPS and the radar signs that clock your speed in 30 limits
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it >>>> actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >>> wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
  Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four
markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
They all agree. 33mph indicated is 30mph actual.
At 40 mph, its 44. at 50 its also 54. At 60 its 65.
I set the cruise control accordingly.
On 14/07/2025 17:45, nib wrote:
On 2025-07-14 17:21, Jeff Layman wrote:
On 14/07/2025 13:59, Nick Finnigan wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the >>>>>> satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it >>>>> actually knows the accurate speed and just chooses to inflate it 10% >>>>> for the
speedo display.
   Does it have some GPS to know the accurate speed? If it is
relying on
wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the
inflated
value, so that the car at 100,000 miles hasn't actually done only
91,000.
   Last time I checked against motorway posts the odometer was more >>>> realistic than the speedometer or mpg calculation (YMMV especially in a >>>> Musk mobile).
That's the way I checked my actual speed, although you tend to err on
the side of caution if you're not exact as the motorway "mileage"
markers are 500 metres apart. So if you measure the time between four
markers, you've done only 1500 metres, whereas a mile is 1609 metres.
Your speed will be 7.25% "high". If you're trying to go by a steady
speed indicated on the speedo, it's even more confusing as you'll have
to add the 7.25% error to the 10% or so error the speedo is already
showing!
The little marker posts are 100 metres apart, so you time 16 intervals,
which is a mile to within about 0.5%.
nib
Good luck trying to keep the count right and, at 60mph, keeping your
eyes off the road for most of a minute looking for the next post.
It is interesting to see the difference between
- lifting off the power when the car remains in gear (reported 999.9 mpg because the inertia of the car is keeping the engine turning so no fuel at all in needed)
- lifting off the power and pressing the clutch (reported 300 mpg approx because the wheels are not turning the engine and so a small amount of fuel is needed to keep it idling)
Nick Finnigan <nix@genie.co.uk> wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10% for the
speedo display.
Does it have some GPS to know the accurate speed? If it is relying on
wheel rotations it needs to know about the tyres.
It's wheel rotations, but if you install the factory size of tyres it knows what the circumference is. Obviously temperature and pressure are going to vary it slightly but only 1-2%, not 10%.
On 14/07/2025 18:22, NY wrote:
It is interesting to see the difference between
- lifting off the power when the car remains in gear (reported 999.9
mpg because the inertia of the car is keeping the engine turning so no
fuel at all in needed)
 ... until the engine speed drops to maybe 1000 rpm.
- lifting off the power and pressing the clutch (reported 300 mpg
approx because the wheels are not turning the engine and so a small
amount of fuel is needed to keep it idling)
 That should vary considerably, depending on the road speed.
On 14/07/2025 18:26, Theo wrote:
It's wheel rotations, but if you install the factory size of tyres it
knows
what the circumference is. Obviously temperature and pressure are
going to
vary it slightly but only 1-2%, not 10%.
 Tread depth will vary it far more.
On 14/07/2025 09:19, Scott wrote:
On Sun, 13 Jul 2025 17:27:17 -0000 (UTC), RJH <patchmoney@gmx.com>
wrote:
On 13 Jul 2025 at 17:44:28 BST, nib wrote:
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
The point is, though, that it's not a petrol car - it's a PHEV.
As OP, I think NY was referring to my car achieving 63.5 mpg. My car I
can assure you is a 2008 Micra and categorically not a hybrid of any
form.
Yes I was.
I still don't understand how PHEVs can be more efficient that pure
petrols because the energy to recharge the battery for the bursts of acceleration in between the low-power cruising still has to come from somewhere - the petrol.
On 14/07/2025 18:26, Theo wrote:
Nick Finnigan <nix@genie.co.uk> wrote:
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it >>>> actually knows the accurate speed and just chooses to inflate it 10%
for the
speedo display.
  Does it have some GPS to know the accurate speed? If it is relying on >>> wheel rotations it needs to know about the tyres.
It's wheel rotations, but if you install the factory size of tyres it
knows
what the circumference is. Obviously temperature and pressure are
going to
vary it slightly but only 1-2%, not 10%.
 Tread depth will vary it far more.
On Mon, 14 Jul 2025 17:40:21 +0100
The Natural Philosopher <tnp@invalid.invalid> wrote:
I use GPS and
the radar signs that clock your speed in 30 limitsI have not found these to be very consistent. There was a period of a
few months when I drove past one three or four times a week, it often
showed the warning when I was 3 or 4 MPH below the limit. At least once
it stayed dark when I went past it at around an indicated 35.
n the mid-70s I coasted downhill in top gear (for engine braking) forNo.
over mile in my Viva HB with the engine switched off. I wondered how
much petrol I would save. As it happened, the answer was a minus figure
- I had forgotten the HB had a mechanical petrol pump and when in gear
it was continuously pumping petrol into the cylinders!
it doing that, the cylinders were so badly flooded it took ages to get
the plugs dry and starting to fire again. I must have used a lot of
extra petrol getting the engine to restart. ðŸ™
You live and learn...
On Mon, 14 Jul 2025 17:40:21 +0100
The Natural Philosopher <tnp@invalid.invalid> wrote:
I use GPS and
the radar signs that clock your speed in 30 limitsI have not found these to be very consistent. There was a period of a
few months when I drove past one three or four times a week, it often
showed the warning when I was 3 or 4 MPH below the limit. At least once
it stayed dark when I went past it at around an indicated 35.
On 14/07/2025 13:10, Theo wrote:
Scott <newsgroups@gefion.myzen.co.uk> wrote:
Read high, surely? Otherwise customers driving at the speed limit
would risk prosecution? Mine reads about 10% high (compared to the
satnav, that I assume must be accurate).
Yes. Mine reads 10% high, but if you look at the speed via OBD-II it
actually knows the accurate speed and just chooses to inflate it 10% for the >> speedo display.
Does it have some GPS to know the accurate speed? If it is relying on
wheel rotations it needs to know about the tyres.
I assume the odometer is measured using the real speed and not the inflated >> value, so that the car at 100,000 miles hasn't actually done only 91,000.
Last time I checked against motorway posts the odometer was more
realistic than the speedometer or mpg calculation (YMMV especially in a
Musk mobile).
I still don't understand how PHEVs can be more efficient that pure
petrols
because the energy to recharge the battery for the bursts of
acceleration in between the low-power cruising still has to come from somewhere - the petrol.
On 13/07/2025 14:11, Scott wrote:
The air conditioning was checked last week and is booked in for a new
condenser on Tuesday. I assume the compressor is okay but I will
certainly ask. The fan is an interesting thought and would explain the
lack of any correlation with steering. Is there an easy way to check?
When the noise occurs stop, open the bonnet, you can usually see the fan >spinning.
On Sun, 13 Jul 2025 14:52:30 +0100, David Wade <g4ugm@dave.invalid>
wrote:
On 13/07/2025 14:11, Scott wrote:
The air conditioning was checked last week and is booked in for a
new condenser on Tuesday. I assume the compressor is okay but I
will certainly ask. The fan is an interesting thought and would
explain the lack of any correlation with steering. Is there an
easy way to check?
When the noise occurs stop, open the bonnet, you can usually see the
fan spinning.
Update. The car has gone to the garage today for the air conditioning condenser to be replaced. He will also check the compressor as part of
the recommissioning of the aircon.
I mentioned the other problems. He will check the fan and the oil for
the differential (which is the same oil as the gearbox). Out of
interest, I asked how this is done and he said it is a sophisticated technique involving removing a bung and sticking a finger through the
hole. Is this SOP?
NY wrote:
I still don't understand how PHEVs can be more efficient that pure
petrols
I think they can only be cheaper* to run if they are charged at home and
used mostly for journeys within their battery range.
On Tue, 15 Jul 2025 10:13:07 +0100
Scott <newsgroups@gefion.myzen.co.uk> wrote:
On Sun, 13 Jul 2025 14:52:30 +0100, David Wade <g4ugm@dave.invalid>
wrote:
On 13/07/2025 14:11, Scott wrote:Update. The car has gone to the garage today for the air conditioning
The air conditioning was checked last week and is booked in for a
new condenser on Tuesday. I assume the compressor is okay but I
will certainly ask. The fan is an interesting thought and would
explain the lack of any correlation with steering. Is there an
easy way to check?
When the noise occurs stop, open the bonnet, you can usually see the
fan spinning.
condenser to be replaced. He will also check the compressor as part of
the recommissioning of the aircon.
I mentioned the other problems. He will check the fan and the oil for
the differential (which is the same oil as the gearbox). Out of
interest, I asked how this is done and he said it is a sophisticated
technique involving removing a bung and sticking a finger through the
hole. Is this SOP?
Very often. In the old rear wheel drive days, the differential had an
oil filler partway up the casing, and the correct level of oil was at
the bottom edge of the filler hole i.e. put oil in until you can't fit
any more in.
On 15 Jul 2025 at 11:20:39 BST, Joe wrote:
On Tue, 15 Jul 2025 10:13:07 +0100
Scott <newsgroups@gefion.myzen.co.uk> wrote:
I mentioned the other problems. He will check the fan and the oil for
the differential (which is the same oil as the gearbox). Out of
interest, I asked how this is done and he said it is a sophisticated
technique involving removing a bung and sticking a finger through the
hole. Is this SOP?
Very often. In the old rear wheel drive days, the differential had an
oil filler partway up the casing, and the correct level of oil was at
the bottom edge of the filler hole i.e. put oil in until you can't fit
any more in.
Same as my Citroen Berlingo.
I still don't understand how PHEVs can be more efficient that pure
petrols
I think they can only be cheaper* to run if they are charged at home and
used mostly for journeys within their battery range.
On Tue, 15 Jul 2025 10:13:07 +0100
Scott <newsgroups@gefion.myzen.co.uk> wrote:
On Sun, 13 Jul 2025 14:52:30 +0100, David Wade <g4ugm@dave.invalid>
wrote:
On 13/07/2025 14:11, Scott wrote:Update. The car has gone to the garage today for the air conditioning
The air conditioning was checked last week and is booked in for a
new condenser on Tuesday. I assume the compressor is okay but I
will certainly ask. The fan is an interesting thought and would
explain the lack of any correlation with steering. Is there an
easy way to check?
When the noise occurs stop, open the bonnet, you can usually see the
fan spinning.
condenser to be replaced. He will also check the compressor as part of
the recommissioning of the aircon.
I mentioned the other problems. He will check the fan and the oil for
the differential (which is the same oil as the gearbox). Out of
interest, I asked how this is done and he said it is a sophisticated
technique involving removing a bung and sticking a finger through the
hole. Is this SOP?
Very often. In the old rear wheel drive days, the differential had an
oil filler partway up the casing, and the correct level of oil was at
the bottom edge of the filler hole i.e. put oil in until you can't fit
any more in.
On 14/07/2025 19:16, Joe wrote:
On Mon, 14 Jul 2025 17:40:21 +0100I don't know quite how much they vary, but making an assumption that
The Natural Philosopher <tnp@invalid.invalid> wrote:
I use GPS and
the radar signs that clock your speed in 30 limitsI have not found these to be very consistent. There was a period of a
few months when I drove past one three or four times a week, it often
showed the warning when I was 3 or 4 MPH below the limit. At least once
it stayed dark when I went past it at around an indicated 35.
those signs represent a gold standard for speed measurement seems
illfounded.
NY wrote:
I still don't understand how PHEVs can be more efficient that pure
petrols
I think they can only be cheaper* to run if they are charged at home and
used mostly for journeys within their battery range.
because the energy to recharge the battery for the bursts of
acceleration in between the low-power cruising still has to come from
somewhere - the petrol.
Your argument seems to be more related to self-charging hybrids than
plug-in hybrids?
[*] yes, cheaper different to efficient.
On 15 Jul 2025 at 09:23:36 BST, Andy Burns wrote:
NY wrote:
I still don't understand how PHEVs can be more efficient that pure
petrols
I think they can only be cheaper* to run if they are charged at home and
used mostly for journeys within their battery range.
I read somewhere that as a rule of thumb, if you pay more than 45p/kWh, petrol's cheaper.
On 14/07/2025 19:18, Jeff Layman wrote:
n the mid-70s I coasted downhill in top gear (for engine braking) forNo.
over mile in my Viva HB with the engine switched off. I wondered how
much petrol I would save. As it happened, the answer was a minus figure
- I had forgotten the HB had a mechanical petrol pump and when in gear
it was continuously pumping petrol into the cylinders!
There was of course a float valve so the fuel pump did not 'pump fuel
into the cylinders'
The carburettor however would suck some fuel in, but normally the engine
would just pump it out again. Surprised you managed to flood it
BTW the correct way to do this is to switch off the engine and then
press the throttle fully down. The air pumping then is a better brake.
On 14/07/2025 23:40, The Natural Philosopher wrote:
On 14/07/2025 19:18, Jeff Layman wrote:
n the mid-70s I coasted downhill in top gear (for engine braking) forNo.
over mile in my Viva HB with the engine switched off. I wondered how
much petrol I would save. As it happened, the answer was a minus figure
- I had forgotten the HB had a mechanical petrol pump and when in gear
it was continuously pumping petrol into the cylinders!
There was of course a float valve so the fuel pump did not 'pump fuel
into the cylinders'
Bad choice of words on my behalf!
The carburettor however would suck some fuel in, but normally the engine
  would just pump it out again. Surprised you managed to flood it
The car was in gear, so the engine was rotating. The only thing which
wasn't happening was a spark as the ignition was turned off. The fuel
pump was driven off the crankshaft (or perhaps the prop shaft;
remember which). As far as the carburettor was concerned, the cylinder
was sucking fuel from it, so as there was a demand the float valve was
not cutting off the petrol. There was no spark so no ignition, and the
petrol sprayed in through the inlet valve would have met a cylinder
which was cooling, albeit slowly. Eventually, the spark gap would have
cooled enough to allow petrol to condense on it. In a way, it's not that different from flooding by too much use of a manual choke when the
engine's cold.
BTW the correct way to do this is to switch off the engine and then
press the throttle fully down. The air pumping then is a better brake.
I don't quite understand. Are you saying I should have done everything
which I did, but /also/ kept the accelerator pedal on the floor?
the way I got the car restarted - kept the accelerator on the floorYup.
while turning the engine continuously with the starter motor. Eventually
the petrol in the flooded cylinder was driven out sufficiently to allow
a spark to form.
On Mon, 14 Jul 2025 17:40:21 +0100
The Natural Philosopher <tnp@invalid.invalid> wrote:
I use GPS and
the radar signs that clock your speed in 30 limitsI have not found these to be very consistent. There was a period of a
few months when I drove past one three or four times a week, it often
showed the warning when I was 3 or 4 MPH below the limit. At least once
it stayed dark when I went past it at around an indicated 35.
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
We drove for about 15 miles at a steady 30MPH, and the car recorded 80MPG.
On 14/07/2025 19:16, Joe wrote:
On Mon, 14 Jul 2025 17:40:21 +0100I find there are two sorts of those signs - the ones that flash and say
The Natural Philosopher <tnp@invalid.invalid> wrote:
I use GPS and
the radar signs that clock your speed in 30 limitsI have not found these to be very consistent. There was a period of a
few months when I drove past one three or four times a week, it often
showed the warning when I was 3 or 4 MPH below the limit. At least once
it stayed dark when I went past it at around an indicated 35.
you are going too fast, and the ones that show your speed.
The former go off when I am doing 25 in a 30.
The latter are within 1MPH checked against GPS calibrated speeds.
Andy
On 13/07/2025 12:54, Scott wrote:
My 2008 Nissan Micra (K12 series) achieved a miles per gallon figure
of 63.5 yesterday on the A74(M) / M74. Is this a record for a petrol
car? I was driving in the 'slow' lane at modest speed because of an
issue (see below).
I was aware of a fairly low-pitched hum coming from the front of the
vehicle. This continued even if I moved the gearbox into neutral and
it seemed to make no difference whether the vehicle was turning or
travelling in a straight line. This seemed to be coming from the
middle, not one wheel. Does this sound like the differential?
My wife's car can show both instantaneous petrol consumption, and
average over a period.
A couple of years ago I found out that the most economical speed is too
slow for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
We drove for about 15 miles at a steady 30MPH, and the car recorded 80MPG.
Andy
On 15/07/2025 21:51, Vir Campestris wrote:
w for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
We drove for about 15 miles at a steady 30MPH, and the car recorded
80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
On 15/07/2025 21:51, Vir Campestris wrote:
w for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
We drove for about 15 miles at a steady 30MPH, and the car recorded 80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
On 15/07/2025 22:09, Jeff Layman wrote:
On 15/07/2025 21:51, Vir Campestris wrote:How else are they supposed to get to the fields? He didnt say motorway.
w for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
Oddly not.,We drove for about 15 miles at a steady 30MPH, and the car recorded
80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
You have a balance between an engine that is not particularly
efficient at low power outputs, because there the friction in the engine
is taking all the power and not the road wheels, and the speed at which
the engine/gearbox reaches higher efficiency, but the aerodynamic drag
starts to dominate.
A light boxy car with a teeny engine is probably best at less than
40mph, but a big engine and decent aero probably means nearer 60mph
On 16/07/2025 00:10, The Natural Philosopher wrote:
On 15/07/2025 22:09, Jeff Layman wrote:
On 15/07/2025 21:51, Vir Campestris wrote:How else are they supposed to get to the fields? He didnt say motorway.
w for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
Absolutely right! I have no idea why I read "dual carriageway" as
"motorway"!
Oddly not.,We drove for about 15 miles at a steady 30MPH, and the car recorded
80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
  You have a balance between an engine that is not particularly
efficient at low power outputs, because there the friction in the engine
is taking all the power and not the road wheels, and the speed at which
the engine/gearbox reaches higher efficiency, but the aerodynamic drag
starts to dominate.
A light boxy car with a teeny engine is probably best at less than
40mph, but a big engine and decent aero probably means nearer 60mph
Well, the OP did state "A couple of years ago I found out that the most economical speed is too slow for my patience." I assumed that he had
tried speeds above 30mph and found a higher fuel consumption.
Anyway, after (trying to!) read this, it's a lot more complicated than I originally thought, and your comment about engine friction vs
aerodynamic drag makes sense: <https://www.amateuraerodynamics.com/2023/10/common-misconceptions-in- aerodynamics.html>
On 2025-07-16 12:55, Jeff Layman wrote:
On 16/07/2025 00:10, The Natural Philosopher wrote:
On 15/07/2025 22:09, Jeff Layman wrote:
On 15/07/2025 21:51, Vir Campestris wrote:How else are they supposed to get to the fields? He didnt say motorway.
w for my patience.
I turned onto a major dual carriageway in a flat part of the country, >>>>> and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
Absolutely right! I have no idea why I read "dual carriageway" as
"motorway"!
Oddly not.,We drove for about 15 miles at a steady 30MPH, and the car recorded
80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
  You have a balance between an engine that is not particularly
efficient at low power outputs, because there the friction in the engine >>> is taking all the power and not the road wheels, and the speed at which
the engine/gearbox reaches higher efficiency, but the aerodynamic drag
starts to dominate.
A light boxy car with a teeny engine is probably best at less than
40mph, but a big engine and decent aero probably means nearer 60mph
Well, the OP did state "A couple of years ago I found out that the
most economical speed is too slow for my patience." I assumed that he
had tried speeds above 30mph and found a higher fuel consumption.
Anyway, after (trying to!) read this, it's a lot more complicated than
I originally thought, and your comment about engine friction vs
aerodynamic drag makes sense:
<https://www.amateuraerodynamics.com/2023/10/common-misconceptions-in-
aerodynamics.html>
Several sites I looked at a while ago suggested that for most cars
slower uses less fuel. One here, for example, admittedly from the US:
https://www.mpgforspeed.com/
I think you maybe have to have a supercar for the most efficient speed
to be anywhere near motorway speed.
nib
snip <
I have a 2008 Peugeot 308 1.6 HDi (diesel). I tend to accelerate
moderately briskly but never tyre-shreddingly! I rarely exceed 70 on a motorway, though I tend always to drive at or slightly below the speed
limit if it's safe to do so (as opposed to choosing to drive much slower
than the limit). I also anticipate in good time so I come off the power
when I see that I will need to slow down, rather than remaining under
power and then braking harder later.
My car has averaged about 55 mpg over its whole 200,000 mile life so
far. I tend to get full-tank to full-tank averages (fuel bought to fill
to pump-shutoff divided by distance since last filling) of about 45-55
mpg. There will be some variation in when a given pump shuts off. When I
was doing a lot of longer journeys on motorways and fast single/dual-carriageways (ie not with much around-town driving) I was averaging around 57 mpg. The best ever tank-to-tank figure was about 63.5.
If you, in a petrol car, can achieve 64, then I'm insanely jealous ;-)
I always fill until I can see the fuel in the filler spout to do my calculation.
On 17/07/2025 10:04, wasbit wrote:
I always fill until I can see the fuel in the filler spout to do my
calculation.
There is a good reason why you should not do that on modern petrol cars.
https://www.youtube.com/watch?v=bb2um2jHRUM
You can damage to the EVAP system and potential issues with the car's performance and emissions.
On 17/07/2025 18:12, alan_m wrote:
On 17/07/2025 10:04, wasbit wrote:
I always fill until I can see the fuel in the filler spout to do my
calculation.
There is a good reason why you should not do that on modern petrol cars.
https://www.youtube.com/watch?v=bb2um2jHRUM
You can damage to the EVAP system and potential issues with the car's
performance and emissions.
It's a diesel.
I have never had a car new enough to have an EVAP system. The filler cap
has always been good enough to stop any escape.
On 18/07/2025 09:19, wasbit wrote:
On 17/07/2025 18:12, alan_m wrote:Or perhaps you simply didn't know it was there?
On 17/07/2025 10:04, wasbit wrote:
I always fill until I can see the fuel in the filler spout to do my
calculation.
There is a good reason why you should not do that on modern petrol cars. >>>
https://www.youtube.com/watch?v=bb2um2jHRUM
You can damage to the EVAP system and potential issues with the car's
performance and emissions.
It's a diesel.
I have never had a car new enough to have an EVAP system. The filler
cap has always been good enough to stop any escape.
On 15/07/2025 21:51, Vir Campestris wrote:
w for my patience.
I turned onto a major dual carriageway in a flat part of the country,
and found just in front of me a tractor. In a contraflow section.
Possibly ok before 1988, but after that it would have been illegal
according to the RTA.
We drove for about 15 miles at a steady 30MPH, and the car recorded
80MPG.
As long as the engine had enough torque to keep in top gear at 30mph,
that would probably have been the sweet spot.
On 15/07/2025 21:45, Vir Campestris wrote:
I find there are two sorts of those signs - the ones that flash andI haven't seen the former for a very long time now.
say you are going too fast, and the ones that show your speed.
The former go off when I am doing 25 in a 30.
The council probably made it a 20mph zone.
Well, the OP did state "A couple of years ago I found out that the most economical speed is too slow for my patience." I assumed that he had
tried speeds above 30mph and found a higher fuel consumption.
| Sysop: | Keyop |
|---|---|
| Location: | Huddersfield, West Yorkshire, UK |
| Users: | 546 |
| Nodes: | 16 (2 / 14) |
| Uptime: | 11:22:23 |
| Calls: | 10,387 |
| Calls today: | 2 |
| Files: | 14,060 |
| Messages: | 6,416,698 |