"NY" wrote in message
o.uk...
"dennis@home" wrote in message
...
On 13/02/2019 21:39, alan_m wrote:
On 13/02/2019 18:12, Robin wrote:

depends on wheel/tyre of course but I was reckoning on tread going from
8mm to 2mm on a tyre of around 180mm circumference.


What about different minor variants of the same basic car? It wouldn't
be unusual for them to be fitted with either,say, 16 or 17 inch wheels.
Do the manufactures adjust the calibration for different factory fitted
wheels or do they rely of range they allowed on the speedo readings?

What about the reading within spec with a space-saver wheel on one
corner



You aren't supposed to drive with the space saver on the front so that
removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver is on
the rear.

People don't of course because they are too idle.

I've not actually heard of that recommendation, though I can see that it
makes sense. It does take a lot longer, because you have to make two
manoeuvres instead of one:

- spare on back to free up a good tyre
- good tyre on front in place of punctured tyre

Mind you, a lot of the time of changing a wheel is initial stuff like
removing stuff from the boot onto the back seat to lift the boot floor to
get at the spare and the jack.

With modern scissor jacks (which have almost no ground clearance for the
handle to turn without grazing your knuckles, it is a thankless task.

Thats why I have a socket that takes the flattened end on the screw
https://www.walmart.ca/en/ip/black-j.../6000093043562
and a ratchet socket driver in with the other tyre tools. Corse
now I have organised that, I wont ever get another flat again.

The last time I had to change a wheel was about 6 months ago when I caught
the inside of a tyre (almost brand new) on the edge of the road surface
that stood proud of a rut beside the road, when an oncoming tractor who
should have given way to me bullied his way forward so I had to veer off
the road to avoid a collision. The tyre held up for another half-mile till
I got home and parked, but a few minutes later a neighbour said "do you
know you've got a flat tyre". That was a waste of £40: there was a huge
gash in the inside wall, a *long* way from the tread so no quibble: the
tyre was unrepeatable.

"dennis@home" wrote in message
...
On 14/02/2019 17:07, NY wrote:
"dennis@home" wrote in message
news
I *thought* that a spacesaver spare tyre was always (nominally) the
same OD as the wheel that it is replacing, allowing for different
amounts of tread wear, and that it was only the tyre *width* that was
narrower. I agree that one wheel may be a different size to the other,
but that is immaterial as long as the OD of the tyre is the same.

They are frequently smaller all around.
The limit to how small they can make them is the clearance on the
brakes.

And how much the car sags at one corner because one wheel is smaller.
When I can be arsed, I'll go and measure my spare against a full-size
wheel. They look the same OD and the car looks level, without a dip at
one corner making the opposite corner high and hence less downward force
on that wheel.

Certainly I've not felt any pulling to one side on the steering, with the
spare on the front or the back - I was amazed at how little it affected
the handling of the car, though I'd be more cautious on cornering and I'd
restrict myself to the 50 mph and 50 miles limit that they always say.

I would check that it doesn't say 50 km/hr.


Gone are the days when your spare is fully-interchangeable with the four
running wheels and can be driven as far and as fast as you like without
any limit. I really wish the UK would mandate cars to be designed so they
can accommodate a full-side spare (steel rather than allow wheel, but
otherwise normal tyre) as used to be the case until corner-cutting took
over. Cars always had a recess in the boot floor or else a cage under the
boot for the full size wheel - or on some cars like the Ford Zephyr and
some small Renaults it was under the bonnet. Nowadays the boot doesn't
seem any more capacious but there's allegedly no room for a full size
wheel in boot - all the pain, but with no perceivable gain.

I think even our big Honda CRV has a space-saver spare, and that's got
plenty of space below the boot floor to take a full-height spare.

Car manufacturers say "oh, it's not a problem - put the spare on and
drive to a tyre place". Not at 10 PM on a Sunday when you're about to
start on a long journey. I don't think I've ever in all the years I've
been driving had a puncture that's happened during shop opening hours -
it's always late at night or on a Sunday that I discover it. Until
recently it was a minor nuisance which delays me setting off by 10 mins
or so to fit the spare, and then take the dead tyre in to be repaired at
a later date when I'm not in a rush to be somewhere. Now it's a
show-stopper which means waiting till the following morning to set off
after I've been to the garage - hoping that they actually have the right
size in stock and I don't have to wait another 24 hours till they've
ordered one in.

Think yourself lucky, they don't do a space saver in my car.
But as its a motability car I might just ignore the flat and drive to a
tyre place if its close or call them out if it isn't.

I suppose I could try the junk in the can first if I can get to the tyre
without getting run down.

The last puncture I had I drove a couple of miles on the M^ roadworks to
avoid stopping on a live lane, its fine as long as you can do at least 50
to keep the tyre up by centripetal forces.

That doesnt happen. The weight of the car
still has the tyre squashed against the road.

Then I had the RAC come and change it while I watched from behind the
barriers.

On 14/02/2019 20:46, Rod Speed wrote:


"dennis@home" wrote in message


8

The last puncture I had I drove a couple of miles on the M^ roadworks
to avoid stopping on a live lane, its fine as long as you can do at
least 50 to keep the tyre up by centripetal forces.

That doesnt happen. The weight of the car
still has the tyre squashed against the road.


That would explain why you can drive for several miles on a motorway
with a flat and only have the tyre shred as you slow down to a stop.

Get with it you are making aussies look stupid.
You make Donk lot like genius.

"dennis@home" wrote in message
...
On 14/02/2019 20:46, Rod Speed wrote:


"dennis@home" wrote in message


8

The last puncture I had I drove a couple of miles on the M^ roadworks to
avoid stopping on a live lane, its fine as long as you can do at least
50 to keep the tyre up by centripetal forces.

That doesnt happen. The weight of the car
still has the tyre squashed against the road.


That would explain why you can drive for several miles on a motorway with
a flat and only have the tyre shred as you slow down to a stop.

That last is a pig ignorant lie and trivial to prove that by
having someone video the wheel from an adjacent car.

On 14/02/2019 15:55, dennis@home wrote:
You aren't supposed to drive with the space saver on the front so that
removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver is
on the rear.

People don't of course because they are too idle.

There are quite a few cars with different size (usually width) tyres
front and rear. It's likely the rear wouldn't go on the front (these are
normally RWD cars)

There is course a reason why you're limited to 90kph with spacesavers.

Andy

On 13/02/2019 16:54, Dave Plowman (News) wrote:
As I said - a very optimistic speedo. Some makers today do just the same.
When making one which is within 1% accuracy should be child's play since
they are counting pulses.

They all do that. 8% high in my experience.

If you aren't careful you won't measure 0-60 times, you'll measure
acceleration to 60 - 8%.

And you'll work out your fuel consumption at a steady 50, not a steady 56...

Win-win for the manufacturer...

I tend to use the tacho. 20MPH per 1000RPM in top, bang on the button,
checked against GPS when straight, level and steady - and I've never
noticed any effect from tyre wear.

The speedo is just somewhere between the marks.

Andy

In article ,
Jim K.. wrote:
Still hopefully the same external diameter, otherwise the car would (try to)
go round in circles.



We call them differentials...

Good luck running different sized tyres on the driven axle. The
differential will over-heat and fail.

--
*Would a fly without wings be called a walk?

Dave Plowman London SW
To e-mail, change noise into sound.

Rod Speed wrote:


"NY" wrote in message
o.uk...
"dennis@home" wrote in message
...
On 13/02/2019 21:39, alan_m wrote:
On 13/02/2019 18:12, Robin wrote:

depends on wheel/tyre of course but I was reckoning on tread going
from 8mm to 2mm on a tyre of around 180mm circumference.


What about different minor variants of the same basic car?Â* It
wouldn't be unusual for them to be fitted with either,say, 16 or 17
inch wheels.
Do the manufactures adjust the calibration for different factory
fitted wheels or do they rely of range they allowed on the speedo
readings?

What about the reading within spec with a space-saver wheel on one
corner



You aren't supposed to drive with the space saver on the front so
that removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver
is on the rear.

People don't of course because they are too idle.

I've not actually heard of that recommendation, though I can see that
it makes sense. It does take a lot longer, because you have to make
two manoeuvres instead of one:

- spare on back to free up a good tyre
- good tyre on front in place of punctured tyre

Mind you, a lot of the time of changing a wheel is initial stuff like
removing stuff from the boot onto the back seat to lift the boot floor
to get at the spare and the jack.

With modern scissor jacks (which have almost no ground clearance for
the handle to turn without grazing your knuckles, it is a thankless task.

Thats why I have a socket that takes the flattened end on the screw
https://www.walmart.ca/en/ip/black-j.../6000093043562
and a ratchet socket driver in with the other tyre tools. Corse
now I have organised that, I wont ever get another flat again.

I have just bought an electric scissors jack.

The last time I had to change a wheel was about 6 months ago when I
caught the inside of a tyre (almost brand new) on the edge of the road
surface that stood proud of a rut beside the road, when an oncoming
tractor who should have given way to me bullied his way forward so I
had to veer off the road to avoid a collision. The tyre held up for
another half-mile till I got home and parked, but a few minutes later
a neighbour said "do you know you've got a flat tyre". That was a
waste of £40: there was a huge gash in the inside wall, a *long* way
from the tread so no quibble: the tyre was unrepeatable.

Harry Bloomfield wrote:
Dave Plowman (News) brought next idea :
Quite. Although even eddy current speedos could be far more accurate than
that spec.

Then there were chronometric ones. You'd laugh at a clock which couldn't
better 10% accuracy even in the 19th century.

Yep, the calibrated speedo in traffic cars.

My ex police bike speedo (cable driven) reads the same as GPS, all other
vehicles have read over.

fred wrote:
On Wednesday, February 13, 2019 at 4:58:16 PM UTC, Dave Plowman (News) wrote:
In article ,
Brian Gaff wrote:
Actually my neighbour had a Metro and boy could that thing move. The
speedo kind of just hit the end and after that it was guesswork. Only
problem with it was that it tended to be full of rust even when new.

As I said - a very optimistic speedo. Some makers today do just the same.
When making one which is within 1% accuracy should be child's play since
they are counting pulses.

--
*The closest I ever got to a 4.0 in school was my blood alcohol content*

Dave Plowman London SW
To e-mail, change noise into sound.

Years ago when speedometers were mechanically driven I had a Cortina with an automatic box. I had always thought it was very noisy at 70 or so mph so I had a friend trail me one night. THe speedo was under reading byt about 8 mph. I often wondered ift they had fitted the wromng cable

Ho do you make a cable that turns at a different speed at the other end?

Dave Liquorice wrote:
On Wed, 13 Feb 2019 21:39:40 +0000, ARW wrote:

The standard of driving on the M1 South of Luton is probably some of the
worst motorway driving I have seen in the UK.

Hum, was down at Milton Keynes and Nottingham last year, thought the
M1 driving was much better than the M6/M61 south of Preston. That's
abit further north I think but the picture of a dragon obscures the
map.

The M1 is mostly "smart motorway" and even without the variable speed
limit in operation everyone one was doing 70 and reasonably well
spaced out. Presumably because some of the VSL gantries also have
ordinary speed cameras bolted on the side...

The M6/M61 is not "smart motorway" and no speed cameras. Any time
near the rush and you'll have cars doing 80+ mph, two car lengths
apart.

The M61 is only 20 miles long, time difference between *average*
speeds of 65 and 75, is a mere 2' 27". Do people really time their
commute so finely? Hitting a couple sets of lights on red instead of
green will add that sort of time...

two feet twenty seven inches ???

"FMurtz" wrote in message
...
Rod Speed wrote:


"NY" wrote in message
o.uk...
"dennis@home" wrote in message
...
On 13/02/2019 21:39, alan_m wrote:
On 13/02/2019 18:12, Robin wrote:

depends on wheel/tyre of course but I was reckoning on tread going
from 8mm to 2mm on a tyre of around 180mm circumference.


What about different minor variants of the same basic car? It
wouldn't be unusual for them to be fitted with either,say, 16 or 17
inch wheels.
Do the manufactures adjust the calibration for different factory
fitted wheels or do they rely of range they allowed on the speedo
readings?

What about the reading within spec with a space-saver wheel on one
corner



You aren't supposed to drive with the space saver on the front so that
removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver is
on the rear.

People don't of course because they are too idle.

I've not actually heard of that recommendation, though I can see that it
makes sense. It does take a lot longer, because you have to make two
manoeuvres instead of one:

- spare on back to free up a good tyre
- good tyre on front in place of punctured tyre

Mind you, a lot of the time of changing a wheel is initial stuff like
removing stuff from the boot onto the back seat to lift the boot floor
to get at the spare and the jack.

With modern scissor jacks (which have almost no ground clearance for the
handle to turn without grazing your knuckles, it is a thankless task.

Thats why I have a socket that takes the flattened end on the screw
https://www.walmart.ca/en/ip/black-j.../6000093043562
and a ratchet socket driver in with the other tyre tools. Corse
now I have organised that, I wont ever get another flat again.

I have just bought an electric scissors jack.

Gotta url ? How well does it work ?

The last time I had to change a wheel was about 6 months ago when I
caught the inside of a tyre (almost brand new) on the edge of the road
surface that stood proud of a rut beside the road, when an oncoming
tractor who should have given way to me bullied his way forward so I had
to veer off the road to avoid a collision. The tyre held up for another
half-mile till I got home and parked, but a few minutes later a
neighbour said "do you know you've got a flat tyre". That was a waste of
£40: there was a huge gash in the inside wall, a *long* way from the
tread so no quibble: the tyre was unrepeatable.

fred wrote:
On Wednesday, February 13, 2019 at 4:58:16 PM UTC, Dave Plowman (News) wrote:
In article ,
Brian Gaff wrote:
Actually my neighbour had a Metro and boy could that thing move. The
speedo kind of just hit the end and after that it was guesswork. Only
problem with it was that it tended to be full of rust even when new.

As I said - a very optimistic speedo. Some makers today do just the same.
When making one which is within 1% accuracy should be child's play since
they are counting pulses.

--
*The closest I ever got to a 4.0 in school was my blood alcohol content*

Dave Plowman London SW
To e-mail, change noise into sound.

Years ago when speedometers were mechanically driven I had a Cortina with
an automatic box. I had always thought it was very noisy at 70 or so mph
so I had a friend trail me one night. THe speedo was under reading byt
about 8 mph. I often wondered ift they had fitted the wromng cable


Why do you believe that your friends speedo was accurate?

A wrong cable cant change the the accuracy but its not unknown for the
wrong speedo drive gears to be fitted to the box resulting in
under-reading. Happened with my wifes old Citroen ZX and it had to be
recalled.

Tim

--
Please don't feed the trolls

Rod Speed wrote:


"FMurtz" wrote in message
...
Rod Speed wrote:


"NY" wrote in message
o.uk...
"dennis@home" wrote in message
...
On 13/02/2019 21:39, alan_m wrote:
On 13/02/2019 18:12, Robin wrote:

depends on wheel/tyre of course but I was reckoning on tread
going from 8mm to 2mm on a tyre of around 180mm circumference.


What about different minor variants of the same basic car?Â* It
wouldn't be unusual for them to be fitted with either,say, 16 or
17 inch wheels.
Do the manufactures adjust the calibration for different factory
fitted wheels or do they rely of range they allowed on the speedo
readings?

What about the reading within spec with a space-saver wheel on one
corner



You aren't supposed to drive with the space saver on the front so
that removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver
is on the rear.

People don't of course because they are too idle.

I've not actually heard of that recommendation, though I can see
that it makes sense. It does take a lot longer, because you have to
make two manoeuvres instead of one:

- spare on back to free up a good tyre
- good tyre on front in place of punctured tyre

Mind you, a lot of the time of changing a wheel is initial stuff
like removing stuff from the boot onto the back seat to lift the
boot floor to get at the spare and the jack.

With modern scissor jacks (which have almost no ground clearance for
the handle to turn without grazing your knuckles, it is a thankless
task.

Thats why I have a socket that takes the flattened end on the screw
https://www.walmart.ca/en/ip/black-j.../6000093043562

and a ratchet socket driver in with the other tyre tools. Corse
now I have organised that, I wont ever get another flat again.

I have just bought an electric scissors jack.

Gotta url ?Â* How well does it work ?

The last time I had to change a wheel was about 6 months ago when I
caught the inside of a tyre (almost brand new) on the edge of the
road surface that stood proud of a rut beside the road, when an
oncoming tractor who should have given way to me bullied his way
forward so I had to veer off the road to avoid a collision. The tyre
held up for another half-mile till I got home and parked, but a few
minutes later a neighbour said "do you know you've got a flat tyre".
That was a waste of £40: there was a huge gash in the inside wall, a
*long* way from the tread so no quibble: the tyre was unrepeatable.

Just ebay electric scissors jack , mine was not from ebay and is el
cheapo 1.5 tonne and takes ages to lift car but it gets there in the end
and is easier than manual

NY laid this down on his screen :
Do traffic cars still use those in preference to GPS?

I'm not familiar with current practice, but I doubt they use still use
magnet/spring speedos, or GPS.

I presume nowadays if
they do measure wheel rotations, everything is electronic, with no moving
parts other than the object that rotates at (a proportion of) wheel speed,
but now sensed by a Hall effect sensor and then rate of pulses (speed)
determined electronically - so there's no spring in the gauge to need to be
recalibrated as it loses its springiness. I wonder if they are recalibrated
periodically as a car's tyres wear down.

I expect the standard traffic car is equipped with just the same system
has our cars have - pulse taken from the ABS of one wheel, then
electronics feeding a stepper motor, except their systems will be set
to display the true speed to +/- 1 mph.

For calibration check, they used to use a process of checking time with
a stopwatch, over a fixed distance at a fixed speed. The tyre wear
makes surprisingly little difference to the calibration. They used to
do that daily.

I used to have a mate who worked on traffic, he then progressed to the
helicopter. So I able to keep in touch with their methods and etc..

On Friday, 15 February 2019 09:13:57 UTC, Harry Bloomfield wrote:
NY laid this down on his screen :

Do traffic cars still use those in preference to GPS?

I'm not familiar with current practice, but I doubt they use still use
magnet/spring speedos, or GPS.

I presume nowadays if
they do measure wheel rotations, everything is electronic, with no moving
parts other than the object that rotates at (a proportion of) wheel speed,
but now sensed by a Hall effect sensor and then rate of pulses (speed)
determined electronically - so there's no spring in the gauge to need to be
recalibrated as it loses its springiness. I wonder if they are recalibrated
periodically as a car's tyres wear down.

I expect the standard traffic car is equipped with just the same system
has our cars have - pulse taken from the ABS of one wheel, then
electronics feeding a stepper motor, except their systems will be set
to display the true speed to +/- 1 mph.

It seems unlikely that they'd use a system that depends on tyre inflation, correct tyre size & tread wear for legal cases. Doppler can be far more accurate.


For calibration check, they used to use a process of checking time with
a stopwatch, over a fixed distance at a fixed speed. The tyre wear
makes surprisingly little difference to the calibration. They used to
do that daily.

I expect now it's done automatically electronically many times a day.


NT

On 15/02/2019 09:13, Harry Bloomfield wrote:
I expect the standard traffic car is equipped with just the same system
has our cars have - pulse taken from the ABS of one wheel, then
electronics feeding a stepper motor, except their systems will be set to
display the true speed to ± 1 mph.

Yes. MOST cars today seem to use that system,

IIRC my jaguar speedos were spot on the money +- tyre wear.

In fact it went beyond that as well - the temeperature gauge was always
once warmed up EXACTLY in the dial ceter even when the warning lights
for overheating gearox came on!


I'd question ABS from ONE wheel. More likely a pair to allow for
cornering etc.



--
The theory of Communism may be summed up in one sentence: Abolish all
private property.

Karl Marx

On 15/02/2019 09:22, wrote:
On Friday, 15 February 2019 09:13:57 UTC, Harry Bloomfield wrote:
NY laid this down on his screen :

Do traffic cars still use those in preference to GPS?

I'm not familiar with current practice, but I doubt they use still use
magnet/spring speedos, or GPS.

I presume nowadays if
they do measure wheel rotations, everything is electronic, with no moving
parts other than the object that rotates at (a proportion of) wheel speed,
but now sensed by a Hall effect sensor and then rate of pulses (speed)
determined electronically - so there's no spring in the gauge to need to be
recalibrated as it loses its springiness. I wonder if they are recalibrated
periodically as a car's tyres wear down.

I expect the standard traffic car is equipped with just the same system
has our cars have - pulse taken from the ABS of one wheel, then
electronics feeding a stepper motor, except their systems will be set
to display the true speed to +/- 1 mph.

It seems unlikely that they'd use a system that depends on tyre inflation, correct tyre size & tread wear for legal cases. Doppler can be far more accurate.

For calibration check, they used to use a process of checking time with
a stopwatch, over a fixed distance at a fixed speed. The tyre wear
makes surprisingly little difference to the calibration. They used to
do that daily.

I expect now it's done automatically electronically many times a day.
There is ample, published material from the police and the NPCC that
shows Harry is right. That is, the police use routinely - and courts
convict on the basis of evidence from - speedometers.



--
Robin
reply-to address is (intended to be) valid

"Robin" wrote in message
...
For calibration check, they used to use a process of checking time with
a stopwatch, over a fixed distance at a fixed speed. The tyre wear
makes surprisingly little difference to the calibration. They used to
do that daily.

I've always thought that timing over a fixed distance is subject to lots of
random errors such as the reaction time of the observer to press the button,
and his judgment as to the exact instant when he has passed the fixed
features such as the white squares painted on the road.

I expect now it's done automatically electronically many times a day.
There is ample, published material from the police and the NPCC that
shows Harry is right. That is, the police use routinely - and courts
convict on the basis of evidence from - speedometers.

Yes, but are the speedometers measuring wheel rotations as for a
conventional speedo (but more accurate), or do they use GPS, or do they use
doppler measured off the road surface (the way that a mouse detects movement
over a mouse mat or desk)?

I suppose a speedo, re-calibrated fairly frequently to adjust for tyre wear,
will be the simplest and most accurate - as long as the spring tension in
the analogue meter is constant throughout the range: I'd have thought that
was the thing that is least easy to control in the manufacture of any
analogue gauge. If the display is digital then as long as the timing crystal
doesn't drift over time, you've eliminated that variable.

In article ,
FMurtz wrote:
Harry Bloomfield wrote:
Dave Plowman (News) brought next idea :
Quite. Although even eddy current speedos could be far more accurate than
that spec.

Then there were chronometric ones. You'd laugh at a clock which couldn't
better 10% accuracy even in the 19th century.

Yep, the calibrated speedo in traffic cars.

My ex police bike speedo (cable driven) reads the same as GPS, all other
vehicles have read over.

Which shows it is possible. Even with ancient technology. Meaning modern
car makers design in the permitted tolerance. Giving, apparently, a faster
car with does more MPG - and also needs servicing earlier. A win win - for
them.

--
*Succeed, in spite of management *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
The Natural Philosopher wrote:
In fact it went beyond that as well - the temeperature gauge was always
once warmed up EXACTLY in the dial ceter even when the warning lights
for overheating gearox came on!

Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.
A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

However, that same BMW had an air to fluid transmission cooler. So no
reason the coolant temperature gauge should show the transmission
overheating.

--
*I have my own little world - but it's OK...they know me here*

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ,
The Natural Philosopher wrote:
In fact it went beyond that as well - the temeperature gauge was always
once warmed up EXACTLY in the dial ceter even when the warning lights
for overheating gearox came on!

Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.
A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

That's interesting. I have always been surprised at how consistent the
indicated temperature of my car is (once it's got up to temperature): I've
never ever seen the needle go above the vertical half-way position, even
when crawling along in a queue of traffic after previously driving at
motorway speed, when previous cars have shown the temperature go up a bit at
first because there's no longer the car's forward-motion draught over the
radiator to supplement the action of the fan in all dumping the heat from
the hard-working engine. Nor does the temperature rise when the engine has
to work hard climbing a long hill.

I'd put it down to a very responsive thermostat and radiator cooling that
was more than enough to keep the coolant down to temperature even in extreme
circumstances.

Maybe the needle is telling porkies... Hopefully it *would* rise into the
danger zone if the coolant really *did* get hot - eg if a hose burst -
otherwise it's not a lot of use in indicating a fault. And I know very well
what happens if a car is run for a long time with no coolant: my sister
trashed the engine of my mum's car when there was a coolant leak. In that
case, she didn't notice that the temperature had gone into the red zone
because the gauge and its warning light were (for some bizarre reason) down
by the gear lever rather than being on the dashboard with the other gauges
and with the warning lights. That was a Renault 14, in case you are
wondering which car had its temperature gauge in such a stupid place.

on 15/02/2019, NY supposed :
I've always thought that timing over a fixed distance is subject to lots of
random errors such as the reaction time of the observer to press the button,
and his judgment as to the exact instant when he has passed the fixed
features such as the white squares painted on the road.

Back then, what better method could they use? A fraction of a second
late or early pressing the button, would not make that much difference
to the check over a 1/4 or 1/2 mile, but they used to allow a bit of
leeway anyway - making sure you were well over the limit.

It happens that The Natural Philosopher formulated :
Yes. MOST cars today seem to use that system,

IIRC my jaguar speedos were spot on the money +- tyre wear.

In fact it went beyond that as well - the temeperature gauge was always once
warmed up EXACTLY in the dial ceter even when the warning lights for
overheating gearox came on!


I'd question ABS from ONE wheel. More likely a pair to allow for cornering
etc.

Again, the error is small enough to be disregarded, were it not, your
ABS would be constantly triggering.

on 15/02/2019, Dave Plowman (News) supposed :
Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.

Mine does that, it is absolutely useless.. It shoots to dead centre as
it warms up and just stays there giving no clues until it has over
heated - entirely pointless.

A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

Mine can be accesses via OBD, or via dash diagnostics - a sequence of
button presses on the odometer reset button.

NY wrote :
Maybe the needle is telling porkies... Hopefully it *would* rise into the
danger zone if the coolant really *did* get hot - eg if a hose burst -
otherwise it's not a lot of use in indicating a fault.

No doubt, but it wouldn't give much warning, just a sudden movement up
to max after the engine has seized. I doubt it would be much help even
if the loss was slow.

That is why they did a little gadget which plugs into the OBD,
indicates true temperature and sounds an alarm over a preset
temperature.

Dave Plowman wrote:

Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.
A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

Mine has reduced the coolant temperature from a gauge on the prior car
(no doubt controlled by the computer rather than a direct read of a
thermocouple) to 8 LEDs, which very quickly reaches the 90°C mark.

Hidden on an 'extra' page of the trip computer is an oil temperature
gauge which takes much longer to reach 90°C, I thought oil would have a
lower specific heat capacity than water, so heat up quicker? Or is the
circulation of oil within the engine that much lower?

On 15/02/2019 09:46, The Natural Philosopher wrote:
On 15/02/2019 09:13, Harry Bloomfield wrote:
I expect the standard traffic car is equipped with just the same
system has our cars have - pulse taken from the ABS of one wheel, then
electronics feeding a stepper motor, except their systems will be set
to display the true speed to ± 1 mph.

Yes. MOST cars today seem to use that system,

I have a speedo display driven from the OBD2
https://www.ebay.co.uk/itm/Car-Head-Up-Display-OBD2-II-HUD-Projector-Speedometer-MPH-KM-h-Speed-Warning-CO/362480289696

It has an ajustment for accuracy, by default that is +8%, and very much
the same as the car's speedo. Setting it to be ±0 gives a speed reading
that's consistent with both a handheld GPS and my phone GPS.


IIRC my jaguar speedos were spot on the money +- tyre wear.

In fact it went beyond that as well - the temeperature gauge was always
once warmed up EXACTLY in the dial ceter even when the warning lights
for overheating gearox came on!


I'd question ABS from ONE wheel. More likely a pair to allow for
cornering etc.





--
djc

(–€Ì¿Ä¹Ì¯–€Ì¿ Ì¿)
No low-hanging fruit, just a lot of small berries up a tall tree.

"Dave Plowman (News)" Wrote in message:
In article ,
Jim K.. wrote:
Still hopefully the same external diameter, otherwise the car would (try to)
go round in circles.



We call them differentials...

Good luck running different sized tyres on the driven axle. The
differential will over-heat and fail.


Good to know your cars are so old they don't have space savers.
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

Harry Bloomfield Wrote in message:
NY wrote :
Maybe the needle is telling porkies... Hopefully it *would* rise into the
danger zone if the coolant really *did* get hot - eg if a hose burst -
otherwise it's not a lot of use in indicating a fault.

No doubt, but it wouldn't give much warning, just a sudden movement up
to max after the engine has seized. I doubt it would be much help even
if the loss was slow.

That is why they did a little gadget which plugs into the OBD,
indicates true temperature and sounds an alarm over a preset
temperature.


Did the Renault 14 have an OBD port?
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

"Jim K.." wrote in message
o.uk...
Harry Bloomfield Wrote in message:
NY wrote :
Maybe the needle is telling porkies... Hopefully it *would* rise into
the
danger zone if the coolant really *did* get hot - eg if a hose burst -
otherwise it's not a lot of use in indicating a fault.

No doubt, but it wouldn't give much warning, just a sudden movement up
to max after the engine has seized. I doubt it would be much help even
if the loss was slow.

That is why they did a little gadget which plugs into the OBD,
indicates true temperature and sounds an alarm over a preset
temperature.


Did the Renault 14 have an OBD port?

I don't know. The car was a Y-suffix so 1983/4. Were OBD ports (and
after-market devices to decode information on the OBD) available in those
days? Goodness knows what Renault were smoking the day they put the
temperature gauge down there. All other cars that I've ever seen, older or
newer, have had the temperature gauge (or at least an over-heat light) on
the dashboard near the speedo, fuel gauge, oil pressure and
dynamo/alternator lights. Even other Renaults had the gauge/light in a
visible location.

I see that the Wikipedia article https://en.wikipedia.org/wiki/Renault_14
mentions it: "The placement of the temperature gauge on the transmission
tunnel behind the gear-lever, rather than on the instrument panel where it
was directly in the driver's field of view, led to incidents of engine
damage if the engine overheated and the driver failed to notice."

"Andy Burns" wrote in message
...
Dave Plowman wrote:

Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't
understand
the true coolant temperature can vary due to driving conditions.
A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

Mine has reduced the coolant temperature from a gauge on the prior car (no
doubt controlled by the computer rather than a direct read of a
thermocouple) to 8 LEDs, which very quickly reaches the 90°C mark.

Hidden on an 'extra' page of the trip computer is an oil temperature gauge
which takes much longer to reach 90°C, I thought oil would have a lower
specific heat capacity than water, so heat up quicker? Or is the
circulation of oil within the engine that much lower?

yep, and no thermostat either.

On Friday, 15 February 2019 21:10:33 UTC, NY wrote:
"Jim K.." wrote in message

Did the Renault 14 have an OBD port?

I don't know. The car was a Y-suffix so 1983/4. Were OBD ports (and
after-market devices to decode information on the OBD) available in those
days?

No

Goodness knows what Renault were smoking

snipped suitably. Some makes I just wouldn't buy.


NT

In article ,
NY wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
The Natural Philosopher wrote:
In fact it went beyond that as well - the temeperature gauge was always
once warmed up EXACTLY in the dial ceter even when the warning lights
for overheating gearox came on!

Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.
A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

That's interesting. I have always been surprised at how consistent the
indicated temperature of my car is (once it's got up to temperature):
I've never ever seen the needle go above the vertical half-way
position, even when crawling along in a queue of traffic after
previously driving at motorway speed, when previous cars have shown the
temperature go up a bit at first because there's no longer the car's
forward-motion draught over the radiator to supplement the action of
the fan in all dumping the heat from the hard-working engine. Nor does
the temperature rise when the engine has to work hard climbing a long
hill.

I'd put it down to a very responsive thermostat and radiator cooling
that was more than enough to keep the coolant down to temperature even
in extreme circumstances.

Maybe the needle is telling porkies... Hopefully it *would* rise into
the danger zone if the coolant really *did* get hot - eg if a hose burst
- otherwise it's not a lot of use in indicating a fault. And I know very
well what happens if a car is run for a long time with no coolant: my
sister trashed the engine of my mum's car when there was a coolant leak.
In that case, she didn't notice that the temperature had gone into the
red zone because the gauge and its warning light were (for some bizarre
reason) down by the gear lever rather than being on the dashboard with
the other gauges and with the warning lights. That was a Renault 14, in
case you are wondering which car had its temperature gauge in such a
stupid place.

They tend to rise very quickly once the normal range is exceeded. The aux
air con fan on mine failed, and it went from the normal reading to near
maximum very quickly when idling in traffic.

--
*I don't believe in astrology. I am a Sagittarius and we're very skeptical.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Harry Bloomfield wrote:
on 15/02/2019, Dave Plowman (News) supposed :
Bosch engine management does this on lots of makes. The gauge isn't
showing true coolant temperature at all. Stays exactly on 'the mark' over
a wide range of normal coolant temps. Ideal for those who can't understand
the true coolant temperature can vary due to driving conditions.

Mine does that, it is absolutely useless.. It shoots to dead centre as
it warms up and just stays there giving no clues until it has over
heated - entirely pointless.

Tend to agree. You might as well just have an overheat light.

But I'm sure it suits those who ain't got a clue how an engine works and
would be worried by knowing the truth. ;-)

A BMW I had allowed you to read true engine temp via the OBC display - if
you knew how to do it.

Mine can be accesses via OBD, or via dash diagnostics - a sequence of
button presses on the odometer reset button.

--
*On the seventh day He brewed beer *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Jim K.. wrote:
Good luck running different sized tyres on the driven axle. The
differential will over-heat and fail.


Good to know your cars are so old they don't have space savers.

No spare of any sort on one of them.

But it's perfectly possible to have a space saver with the same rolling
radius as a full sized wheel.

Oh - sorry. Forgot it was you. Get someone to explain rolling radius to
you.

--
*If you think this van is dirty, you should try having sex with the driver*

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Jim K.. wrote:
Good luck running different sized tyres on the driven axle. The
differential will over-heat and fail.


Good to know your cars are so old they don't have space savers.

No spare of any sort on one of them.

But it's perfectly possible to have a space saver with the same rolling
radius as a full sized wheel.

Of course it is, but then it wouldnt save as much space. Manufactures are
supplying space savers with a smaller radius.


Oh - sorry. Forgot it was you. Get someone to explain rolling radius to
you.


Maybe you ought to fact check space saver sizes rather than assuming that
they must be the same diameter.

Tim

--
Please don't feed the trolls

Dave Plowman (News) wrote:
In article ,
Jim K.. wrote:
Still hopefully the same external diameter, otherwise the car would (try to)
go round in circles.



We call them differentials...

Good luck running different sized tyres on the driven axle. The
differential will over-heat and fail.


Sounds improbable. Maybe a limited slip diff wouldnt like it but I cant
see a regular diff being seriously stressed by a small difference in
rolling radius. Many space savers *are* smaller in terms of overall
diameter/rolling radius.

Tim

--
Please don't feed the trolls

Dave Plowman (News) expressed precisely :
Which shows it is possible. Even with ancient technology. Meaning modern
car makers design in the permitted tolerance. Giving, apparently, a faster
car with does more MPG - and also needs servicing earlier. A win win - for
them.

The speedo's are usually optimistic, but not the odometers. They are
usually very accurate.

"Tim+" wrote in message
news:1919761807.571994810.278464.tim.downie- But it's perfectly possible
to have a space saver with the same rolling
radius as a full sized wheel.

Of course it is, but then it wouldnt save as much space. Manufactures are
supplying space savers with a smaller radius.

As a matter of interest, how much smaller diameter are we talking about?

Oh - sorry. Forgot it was you. Get someone to explain rolling radius to

Maybe you ought to fact check space saver sizes rather than assuming that
they must be the same diameter.

You may well be right. I'm intrigued. I'll do some measurements. I always
assumed that the diameter was identical and that all the saving was in the
*width* of the tyre, on the maybe naive assumption that if you put a smaller
tyre on one axle, the car will want to go round in circles - irrespective of
whether the wheels are joined by a differential (front wheel) or are totally
independent of each other (rear wheel) - and will dip down at that corner,
putting less weight (and so less traction if the opposite wheel is a driving
wheel) on the diagonally opposite wheel.