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On Sep 10, 3:07*pm, Grimly Curmudgeon wrote:
On Mon, 10 Sep 2012 01:16:38 -0700 (PDT), harry
wrote:

There is always "microslippage" between wheel and road. Even more when
cornering.


TNP has a fizziks degree; he knows better than everyone who doesn't.


He has a degree in Janatorial studies
Or possibly TV studies
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harry wrote:
On Sep 10, 3:07 pm, Grimly Curmudgeon wrote:
On Mon, 10 Sep 2012 01:16:38 -0700 (PDT), harry
wrote:

There is always "microslippage" between wheel and road. Even more when
cornering.

TNP has a fizziks degree; he knows better than everyone who doesn't.


He has a degree in Janatorial studies
Or possibly TV studies


I told you that you don't get to understand me by looking in a mirror Harry.


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In article ,
The Natural Philosopher wrote:
The dominant rolling resistance of a tyred car is down to deformation
and hysteresis.


And deformation of the tyre generates friction...

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Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
The dominant rolling resistance of a tyred car is down to deformation
and hysteresis.


And deformation of the tyre generates friction...


No it doesn't. Not in the accepted sense of that word, because
deformation of a perfectly elastic medium is possible without energy
loss at all.

E,.g a coil spring does not get very hot ....


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In article ,
The Natural Philosopher wrote:
And deformation of the tyre generates friction...


No it doesn't. Not in the accepted sense of that word, because
deformation of a perfectly elastic medium is possible without energy
loss at all


Which tyres ain't.

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On 09/09/2012 20:10, The Natural Philosopher wrote:
Andy Champ wrote:
On 09/09/2012 15:27, The Natural Philosopher wrote:
Whether you call that friction is up to you. Personally I dont.
Friction to me is sliding contact between hard surfaces, or fluid over
a surface.

If you did in fact have a classic frictional case as a boat hull in
water, you very quickly find that cars go faster than boats of the same
weight for the same power


That depends. At very low speed the friction of a floating object is
negligible; that isn't true of a car. I'll happily push a 10 tonne
boat off from a jetty, but I wouldn't even try with a truck.


Tyre rolling resistance represents almost a fixed drag component
irrespective of speed.


Boat hull resistance is purely a function of wetted area and speed.


I see you don't sail much.

Au contraire getting a boat to plane is about getting the wetted area down


Nope. Getting planing is all about the wave systems. Once you are
planing things change; 10 tonnes being pushed off a jetty isn't planing.
Once planing the hull shape is also pretty important - try tying a
bucket to an outboard leg, and see how well a motor boat planes. And
think how small a proportion of the wetted area that is.


Air resistance is more complex, because air is more compressible. Its a
function of frontal area and shape.


... and you won't notice the compressibility of air until you get to a
substantial fraction of the speed of sound.

I see you dont do physics or aeronautics. OR have a car with tyres that
are inflated.


OK, so just how much does the air compress around a car at 70MPH?

The compressed air in the tyres isn't relevant to the air drag.

Andy
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In message , Andy Champ
writes
On 09/09/2012 17:57, Bill wrote:

A displacement boat has a "natural" maximum speed (the hull speed)
dependent on the hull length. I've often wondered if something similar
applies to cars in air.

It might explain why in the old Omega, fuel consumption on the motorway
only went skywards over 70, but my current vehicle is bad over 60.


Or it might not.

Hull speed is when you are travelling at about the same speed as a wave
of the same length. Increase speed and your stern wave falls behind, so
you are climbing a wave at the front but not getting pushed by the
stern wave behind - and power needed goes up.

In a car air resistance is proportional to the square of the speed.
(and power to the cube). So go faster, use much more fuel. And you
get odd effects in engine efficiency too - petrol engines are really
inefficient at low power settings, so go a little faster and you may
get better fuel economy especially on a large petrol engine. I'm
guessing the Omega wasn't a diesel? And that the current car has a
smaller engine?

Well yes, the Omegas and Carltons were all petrol 2.2 or 2.0 litre. The
current thing is a 1.9tdi Skoda, which is still fairly long, so I
suppose petrol may be better at higher speeds. Be interesting to compare
notes with a petrol Octavia.

The crucial thing for me was that a change in lifestyle brought the need
to do innumerable short trips with a lot of waiting time. The Omega on
almost permanent full choke did between 6 to 9 mpg, compared with its
40mpg at 70 on the motorway. The Octavia on a good day with all the
lights in its favour has done 70mpg across Wales and back at a moderate
speed and does about 40mpg on the stop wait start cycle.

I take issue with the motoring writers who constantly say that you have
to do a huge mileage for a diesel to be sensible. Of course if the turbo
falls to bits into the engine, I might change my mind.
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Andy Champ wrote:
On 09/09/2012 20:10, The Natural Philosopher wrote:
Andy Champ wrote:
On 09/09/2012 15:27, The Natural Philosopher wrote:
Whether you call that friction is up to you. Personally I dont.
Friction to me is sliding contact between hard surfaces, or fluid over
a surface.

If you did in fact have a classic frictional case as a boat hull in
water, you very quickly find that cars go faster than boats of the same
weight for the same power

That depends. At very low speed the friction of a floating object is
negligible; that isn't true of a car. I'll happily push a 10 tonne
boat off from a jetty, but I wouldn't even try with a truck.


Tyre rolling resistance represents almost a fixed drag component
irrespective of speed.


Boat hull resistance is purely a function of wetted area and speed.

I see you don't sail much.

Au contraire getting a boat to plane is about getting the wetted area
down


Nope. Getting planing is all about the wave systems. Once you are
planing things change; 10 tonnes being pushed off a jetty isn't planing.
Once planing the hull shape is also pretty important - try tying a
bucket to an outboard leg, and see how well a motor boat planes. And
think how small a proportion of the wetted area that is.


Air resistance is more complex, because air is more compressible.
Its a
function of frontal area and shape.

... and you won't notice the compressibility of air until you get to a
substantial fraction of the speed of sound.

I see you dont do physics or aeronautics. OR have a car with tyres that
are inflated.


OK, so just how much does the air compress around a car at 70MPH?

depends. Maybe a few PSI.

Ask McLaren.

Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


The compressed air in the tyres isn't relevant to the air drag.

Andy



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In article ,
Bill wrote:
The crucial thing for me was that a change in lifestyle brought the need
to do innumerable short trips with a lot of waiting time. The Omega on
almost permanent full choke did between 6 to 9 mpg, compared with its
40mpg at 70 on the motorway.


Sounds like poor design. My 3.5 Rover auto - '85 - does 15 mpg on short
trips, like down to the shops in winter. Even an old 4.2 Jag I had on
carburettors with an auto choke did better than your Omega.

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In article ,
The Natural Philosopher wrote:
OK, so just how much does the air compress around a car at 70MPH?

depends. Maybe a few PSI.


Ask McLaren.


Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.

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On Tue, 11 Sep 2012 00:20:14 +0100, "Dave Plowman (News)"
wrote:

Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.


Unless he was an ace at it.
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In message , "Dave Plowman (News)"
writes
In article ,
The Natural Philosopher wrote:
OK, so just how much does the air compress around a car at 70MPH?

depends. Maybe a few PSI.


Ask McLaren.


Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.

Well, aksh

(turn thenm upside down and ...)


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geoff
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Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
OK, so just how much does the air compress around a car at 70MPH?

depends. Maybe a few PSI.


Ask McLaren.


Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.

I am beginning to wonder about you Dave.

You aren't Drivel under a new name are you?

All of formula 1 is about aerodynamics - using air pressure to produce
lift downwards..


Air pressure changes are inevitable in any body moving through air. When
these result in turbulence and vortices these become where the energy
goes that causes the actual profile drag.

Skin friction is also an affect, but at car sizes and speeds is not a
huge component.

What dominates low speed drag is a more or less constant rolling
resistance due to tyre deformation: What dominates higher speeds is air
resistance associated with pressure changes and vortex formation round
the bodywork



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In article ,
Grimly Curmudgeon wrote:
Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.


Unless he was an ace at it.


;-)

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In article ,
The Natural Philosopher wrote:
Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.

I am beginning to wonder about you Dave.


You aren't Drivel under a new name are you?


Just answering your irrelevances with some of my own...

All of formula 1 is about aerodynamics - using air pressure to produce
lift downwards..


Which makes for inefficiency. It may well help the car to corner faster -
but in doing so will use more energy. You don't get out for nowt.

Air pressure changes are inevitable in any body moving through air. When
these result in turbulence and vortices these become where the energy
goes that causes the actual profile drag.


Skin friction is also an affect, but at car sizes and speeds is not a
huge component.


What dominates low speed drag is a more or less constant rolling
resistance due to tyre deformation: What dominates higher speeds is air
resistance associated with pressure changes and vortex formation round
the bodywork


If it were only tyre rolling resistance, how do you explain 4WD being
markedly heavier on fuel than 2WD?

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The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
OK, so just how much does the air compress around a car at 70MPH?

depends. Maybe a few PSI.
Ask McLaren.
Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.
Planes have wings specifically designed to produce lift. Only the most

stupid card designer would use the same effect.
I am beginning to wonder about you Dave.


You aren't Drivel under a new name are you?

All of formula 1 is about aerodynamics - using air pressure to produce lift downwards..


No it's not. Why not stick to subjects that you know about? The silence
would be refreshing.

Formula 1 balances many requirements of which aerodynamic performance is
one component and downforce is one element of that component.
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Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.
Planes have wings specifically designed to produce lift. Only the most
stupid card designer would use the same effect.

I am beginning to wonder about you Dave.


You aren't Drivel under a new name are you?


Just answering your irrelevances with some of my own...

All of formula 1 is about aerodynamics - using air pressure to produce
lift downwards..


Which makes for inefficiency. It may well help the car to corner faster -
but in doing so will use more energy. You don't get out for nowt.


Oh. You have moved the goalposts AGAIN. You contention was that cars
dint cause air pressure changes.

Air pressure changes are inevitable in any body moving through air. When
these result in turbulence and vortices these become where the energy
goes that causes the actual profile drag.


Skin friction is also an affect, but at car sizes and speeds is not a
huge component.


What dominates low speed drag is a more or less constant rolling
resistance due to tyre deformation: What dominates higher speeds is air
resistance associated with pressure changes and vortex formation round
the bodywork


If it were only tyre rolling resistance, how do you explain 4WD being
markedly heavier on fuel than 2WD?

Largely because they are built like tanks



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In message , "Dave Plowman (News)"
writes
Sounds like poor design. My 3.5 Rover auto - '85 - does 15 mpg on short
trips, like down to the shops in winter. Even an old 4.2 Jag I had on
carburettors with an auto choke did better than your Omega.


I should have said that it was auto, of course. Unfortunately I never
did the same sort of driving in the 3 previous Omegas, all of which were
far better vehicles than that last one. Maybe it was just a dud.
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In article ,
The Natural Philosopher wrote:
Which makes for inefficiency. It may well help the car to corner
faster - but in doing so will use more energy. You don't get out for
nowt.


Oh. You have moved the goalposts AGAIN. You contention was that cars
dint cause air pressure changes.


No I didn't. Anything which moves causes an air pressure change.

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On 08/09/2012 07:15, harry wrote:
On Sep 7, 6:45 pm, Andy Cap wrote:
On 07/09/12 18:40, harryagain wrote:

Drove an electric car today.
Uncanny experience but good.
http://www.mitsubishi-cars.co.uk/imiev/technology.aspx


... and the batteries last how long and cost what to replace?

Andy C



Range is 83 miles. Batteries guaranteed for 5-10 years (Dependingon
how you treat them.). Replacement cost around £4,000


Within the 5-10 year period, the value of the average family car falls
to £4,000, who would want to spend an amount equal to the entire value
of an 'old' car to keep it on the road, when they are fed up of it and
it's beginning to look a little worn around the edges?

SteveW



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On 10/09/2012 22:29, The Natural Philosopher wrote:
depends. Maybe a few PSI.

Ask McLaren.

Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


OK, so I'll dig it out. This google find me a Spit (of some sort or
other!) has about 22 sq metres of wing area, and 2600Kg. So 26Kn/22 sq
metres ~= 1.2kPa. Or just over 1% of an atmosphere.

Boyle's law will give you a similar compresssion. Shall we say 2% at
peak, seeing as it isn't the same over the whole wing?

Wind pressure with a wind speed approximating to motorway speeds seems
to be about 0.5kPa. Even less.

I really think you won't notice.

Andy
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Andy Champ wrote:
On 10/09/2012 22:29, The Natural Philosopher wrote:
depends. Maybe a few PSI.

Ask McLaren.

Or an aircraft designer. Enough to create a pressure difference big
enough to keep a plane up.


OK, so I'll dig it out. This google find me a Spit (of some sort or
other!) has about 22 sq metres of wing area, and 2600Kg.


So far so good

So 26Kn

I think you missed out the ability of a spitty to pull 6 g in a turn

So thats 25497.29 * 6=

/22 sq
metres ~= 1.2kPa. Or just over 1% of an atmosphere.

so abiout 7% of an atm,ospere



Boyle's law will give you a similar compresssion. Shall we say 2% at
peak, seeing as it isn't the same over the whole wing?


More like 15% when pulling hard..

Wind pressure with a wind speed approximating to motorway speeds seems
to be about 0.5kPa. Even less.

I really think you won't notice.


well you would actually. Since a car is not a very aerodynamic device

Wings are designed to be low drag high lift devices. Cars suffer from
form drag.

In essence the way to understand this is as a pressure differentual
between the front and the back: the lack of laminar flow at the rear
where the flow breaks into vortices at high reynolds numbers creates a
partial vacuum behind the car and the compression of the air in front
creates a pressure rise.

The difference is the drag

http://en.wikipedia.org/wiki/Drag_equation#Derivation



Andy



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Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
It's the major factor. In still water a single person can move a ship
weighing many tons. You'll not do that with a similar weight vehicle.


Due to the tyre rolling resistance.


I can in fact push a van weighing several toinnes on well pumped up
tyres on a dead smooth flat road.


I'm talking about a small ship like say a trawler where I've seen it done.

I'll bet you'll not move a truck weighing anywhere near as much.

Ah but a ship is weightless because its weight is in equilibrium with
the water it displaces. Otherwise it would sink...

On a related topic, how come the small bit of tyre that touches the
ground can support a van? There might be 40psi in the tyres, but
multiply that by the area of tyre touching the road and it doesn't seem
to come to much. It must do though.

Time for a snooze I think. All this hard thinking is beginning to hurt.

Bill
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The Natural Philosopher wrote:

Boat hull resistance is purely a function of wetted area and speed.


It's lucky it's a function of speed or when you jumped into a rowing
boat it would shoot to the other bank and get stuck in the mud.

Bill
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Andy Champ wrote:

That depends. At very low speed the friction of a floating object is
negligible; that isn't true of a car. I'll happily push a 10 tonne boat
off from a jetty, but I wouldn't even try with a truck.

Well you wouldn't be allowed to anyway. The driver would be hopping mad.

Bill


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Grimly Curmudgeon wrote:

So, without friction,
you'd be ****ed.


That's the best way to be ****ed.

Bill
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harry wrote:

Hysteresis is what wastes power in tyres. (ie flexing them).
The higher the tyre pressure the less flex and less energy lost.


And when they flex the two sides rub on the road in opposite directions,
so that's friction.

Bill
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The Natural Philosopher wrote:

not at the pint of contact.

Only an infinitely hard wheel on an infinitely hard road would waste no
energy on deforming the road or the wheel.

Bill
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Bill Wright wrote:
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
It's the major factor. In still water a single person can move a ship
weighing many tons. You'll not do that with a similar weight vehicle.


Due to the tyre rolling resistance.


I can in fact push a van weighing several toinnes on well pumped up
tyres on a dead smooth flat road.


I'm talking about a small ship like say a trawler where I've seen it
done.

I'll bet you'll not move a truck weighing anywhere near as much.

Ah but a ship is weightless because its weight is in equilibrium with
the water it displaces. Otherwise it would sink...

On a related topic, how come the small bit of tyre that touches the
ground can support a van? There might be 40psi in the tyres, but
multiply that by the area of tyre touching the road and it doesn't seem
to come to much. It must do though.

Time for a snooze I think. All this hard thinking is beginning to hurt.


Well there are 4 tyres.. so if the van is two tons that's 1/2 ton per
wheel. say 1000 lb each wheel. and at 40 psi that's 25 sq in per tyre.

that's only 8x3.125" and a van tyre is easily 8" across


Bill



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Bill Wright wrote:
The Natural Philosopher wrote:

Boat hull resistance is purely a function of wetted area and speed.


It's lucky it's a function of speed or when you jumped into a rowing
boat it would shoot to the other bank and get stuck in the mud.

no you wouldnt.

Bill



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Bill Wright wrote:
harry wrote:

Hysteresis is what wastes power in tyres. (ie flexing them).
The higher the tyre pressure the less flex and less energy lost.


And when they flex the two sides rub on the road in opposite directions,


What ARE you talking about. The sidewalls don't touch the road.

so that's friction.


No, its simple stupidity.


Bill



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Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
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In message , Bill Wright
writes
Grimly Curmudgeon wrote:
So, without friction,
you'd be ****ed.


That's the best way to be ****ed.

God won't love you ...


--
geoff
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Bill Wright wrote:
The Natural Philosopher wrote:

not at the pint of contact.

Only an infinitely hard wheel on an infinitely hard road would waste no
energy on deforming the road or the wheel.


deformation is not friction. Nor does it cause it.

I agree with you: That is not what we were talking about.

To repeat: at low speeds the major drag on a car is due to rolling
resistance which is 90% or more about tyre deformation, not friction.

I don't see why this is so hard to grasp.


Bill



--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
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"harryagain" wrote in message
...
Drove an electric car today.
Uncanny experience but good.
http://www.mitsubishi-cars.co.uk/imiev/technology.aspx


I drove the Ampera. Fanastic to drive. Quiet as hell.

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Dave Liquorice wrote:
On Fri, 7 Sep 2012 21:30:56 +0100, tony sayer wrote:

Well it sez a 93 mile range which I suppose would suit me a lot of
the time ...


My round trip working tommorow will be 110 miles. Monday's is around
240.


Then buy an Ampera


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SteveW wrote:
On 08/09/2012 07:15, harry wrote:
On Sep 7, 6:45 pm, Andy Cap wrote:
On 07/09/12 18:40, harryagain wrote:

Drove an electric car today.
Uncanny experience but good.
http://www.mitsubishi-cars.co.uk/imiev/technology.aspx

... and the batteries last how long and cost what to replace?

Andy C



Range is 83 miles. Batteries guaranteed for 5-10 years (Dependingon
how you treat them.). Replacement cost around £4,000


Within the 5-10 year period, the value of the average family car falls
to £4,000, who would want to spend an amount equal to the entire value
of an 'old' car to keep it on the road, when they are fed up of it and
it's beginning to look a little worn around the edges?


Battery technology is improving greatly. There is also the combined
battery/supercapacitor. You could have a 10 year old car and slap in a new
battery set and it is transformed.

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In article ,
Doctor Drivel wrote:
Battery technology is improving greatly. There is also the combined
battery/supercapacitor.


This could have been posted 30 years ago. And was as true then as now. Or
not.

--
*If only you'd use your powers for good instead of evil.

Dave Plowman London SW
To e-mail, change noise into sound.
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On Sunday, September 9, 2012 11:18:21 AM UTC+1, tony sayer wrote:
In article, Dave Plowman (News)

dave scribeth thus

In article


,


harry wrote:


... and the batteries last how long and cost what to replace?




Andy C






Range is 83 miles. Batteries guaranteed for 5-10 years (Dependingon


how you treat them.). Replacement cost around £4,000




Treat them? Leave it in the garage on charge but never driven to get the


10 year warranty? And is the warranty free replacement or a proportional


cost according to age?




Tesla, for example, won't do a warranty replacement if the car is unused


and not on charge for a few weeks - like say left at an airport carpark


while on holiday.






Hrump!, The car under discussion wouldn't get me to the main Two London

airports and its very marginal if it could do a return trip to the

nearest one!..



Electric makes most sense with short range microcars. Microcars use less energy per mile, reducing battery weight and cost for a given range. Short ranges only mean a major reduction in battery cost and weight, and thus again energy use. So if you live on the edge of town and only want the car to head into town and back with, and you're not getting out of 30mph zones, a lead acid mcirocar can make sense to an extent. But only if you're ok with its various downsides. Such a beast can be homebuilt cheaply, but with all the issues it won't suit many people.

Full size electric cars don't make good sense today. Maybe they will with some as yet unknown battery technology that combines low cost, weight and charge time.


NT
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Just as we get shot of wodney;

On 11/09/2012 23:39, Doctor Drivel wrote:

I drove the Ampera. Fanastic to drive. Quiet as hell.


Long time no hear dribble... what brings you back?


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Cheers,

John.

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On Sep 11, 9:47*pm, Bill Wright wrote:
The Natural Philosopher wrote:
not at the pint of contact.


Only an infinitely hard wheel on an infinitely hard road would waste no
energy on deforming the road or the wheel.

Bill



But then the pressure would be infinite and the contact area zero, so
where does that leave you?
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