On Friday, 30 January 2015 17:36:21 UTC, Malcolm Race wrote:
I have recently bought a Zafira. I was surprised to see that the tyre
pressures were 36psi. I previously owned an Astra Estate (similar size
and weight) whith tyre pressures of 29psi. When I looked in the manual,
two pressures were quoted - 29psi for 'comfort' and 36psi for 'eco'.

I understand that running tyres at higher pressures meant that there
would be more wear in the centre of the tyre.

My inclination is to reduce the pressure to 29psi to obtain the maximum
tyre wear.

Does anyone have any views on this?

How will rigidity affect the wheel rims?
If they are low profile, aluminium wheels I would go for the higher value. If you have potholes in your area, that could save a lot of money.

On Saturday, 31 January 2015 13:21:26 UTC, Adrian wrote:

..the life-limiting factor on the over-inflated tyre...

If the manufacturer recommends it, it isn't over inflated.

On 02/02/2015 22:57, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 21:46, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 13:48, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
I'm not convinced that you do see less rubber in
contact with the asphalt with those two pressures.

Well, it's pounds per square inch, innit. Your car weight is
constant,
so the lower the tyre pressure, the greater the contact area.

Don't think that is necessarily so

Radial ply tyres have a different construction to the tread area over
the
sidewalls. Just how that reacts to varying pressure isn't a constant.
I'd
say it is designed to give the correct 'footprint' at the correct
load/pressure. Altering either won't automatically give a greater or
lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same?

We aren't talking about a sensible range, we are discussing
whether the amount of rubber into contact with the road
varys significantly with the two pressures in the manual.

I don’t believe that there is any real evidence that it does
and that the main effect is on the amount of sidewall
flexing that you get with the car being driven around.

I know where my money is - there's usually upwards of a quarter of a
tonne on each tyre.

But the rubber in contact with the road is the least
flexible part of the tyre with the exception of the
part of the tyre that is in contact with the rim itself.

And it wouldn’t be hard to measure how much the
area in contact with the road changes with those
two pressures. I bet its **** all.

Ok, I have physics, albeit idealised. I have links, here's one...

http://en.wikipedia.org/wiki/Contact_patch

That one doesn’t even mention what the difference would
be in the area in contact with the road with the two pressures
we are discussing.

...but you can use Google too.

Which doesn’t tell us what the different contact area
would be with the tyres and pressures being discussed.

What do you have, religion?

Nope, measurement, as I said.

Leaves your waffle for dead.


What measurement? The measurement that "it wouldn't be hard" to make?
Where can I see these?

Put up or **** off, you wilfully ignorant ******.

Cheers
--
Syd

"Syd Rumpo" wrote in message
...
On 02/02/2015 22:57, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 21:46, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 13:48, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
I'm not convinced that you do see less rubber in
contact with the asphalt with those two pressures.

Well, it's pounds per square inch, innit. Your car weight is
constant,
so the lower the tyre pressure, the greater the contact area.

Don't think that is necessarily so

Radial ply tyres have a different construction to the tread area over
the
sidewalls. Just how that reacts to varying pressure isn't a constant.
I'd
say it is designed to give the correct 'footprint' at the correct
load/pressure. Altering either won't automatically give a greater or
lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same?

We aren't talking about a sensible range, we are discussing
whether the amount of rubber into contact with the road
varys significantly with the two pressures in the manual.

I don’t believe that there is any real evidence that it does
and that the main effect is on the amount of sidewall
flexing that you get with the car being driven around.

I know where my money is - there's usually upwards of a quarter of a
tonne on each tyre.

But the rubber in contact with the road is the least
flexible part of the tyre with the exception of the
part of the tyre that is in contact with the rim itself.

And it wouldn’t be hard to measure how much the
area in contact with the road changes with those
two pressures. I bet its **** all.

Ok, I have physics, albeit idealised. I have links, here's one...

http://en.wikipedia.org/wiki/Contact_patch

That one doesn’t even mention what the difference would
be in the area in contact with the road with the two pressures
we are discussing.

...but you can use Google too.

Which doesn’t tell us what the different contact area
would be with the tyres and pressures being discussed.

What do you have, religion?

Nope, measurement, as I said.

Leaves your waffle for dead.


What measurement? The measurement that "it wouldn't be hard" to make?
Where can I see these?

Put up or **** off, you wilfully ignorant ******.

Cheers

LOL
Our Wodders isn't doing too well tonight.

"Syd Rumpo" wrote in message
...
On 02/02/2015 22:57, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 21:46, Rod Speed wrote:


"Syd Rumpo" wrote in message
...
On 02/02/2015 13:48, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
I'm not convinced that you do see less rubber in
contact with the asphalt with those two pressures.

Well, it's pounds per square inch, innit. Your car weight is
constant,
so the lower the tyre pressure, the greater the contact area.

Don't think that is necessarily so

Radial ply tyres have a different construction to the tread area over
the
sidewalls. Just how that reacts to varying pressure isn't a constant.
I'd
say it is designed to give the correct 'footprint' at the correct
load/pressure. Altering either won't automatically give a greater or
lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same?

We aren't talking about a sensible range, we are discussing
whether the amount of rubber into contact with the road
varys significantly with the two pressures in the manual.

I don’t believe that there is any real evidence that it does
and that the main effect is on the amount of sidewall
flexing that you get with the car being driven around.

I know where my money is - there's usually upwards of a quarter of a
tonne on each tyre.

But the rubber in contact with the road is the least
flexible part of the tyre with the exception of the
part of the tyre that is in contact with the rim itself.

And it wouldn’t be hard to measure how much the
area in contact with the road changes with those
two pressures. I bet its **** all.

Ok, I have physics, albeit idealised. I have links, here's one...

http://en.wikipedia.org/wiki/Contact_patch

That one doesn’t even mention what the difference would
be in the area in contact with the road with the two pressures
we are discussing.

...but you can use Google too.

Which doesn’t tell us what the different contact area
would be with the tyres and pressures being discussed.

What do you have, religion?

Nope, measurement, as I said.

Leaves your waffle for dead.


What measurement? The measurement that "it wouldn't be hard" to make?

Yep.

Where can I see these?

Where ever you choose to put them when you do that, ****wit.

On Mon, 02 Feb 2015 15:40:26 +0000, Syd Rumpo
wrote:

On 02/02/2015 15:27, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
Radial ply tyres have a different construction to the tread area over
the sidewalls. Just how that reacts to varying pressure isn't a
constant. I'd say it is designed to give the correct 'footprint' at
the correct load/pressure. Altering either won't automatically give a
greater or lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same? I know where my money is - there's usually upwards of a quarter
of a tonne on each tyre.

If the tread 'belt' is made sort of concave, you might actually reduce the
contact area if you deflate from the correct pressure. Until the tyre is
nearly flat. In which case the 'grip' ain't going to matter much.

Well, I realise that the physics only applies fully to an idealised
tyre, but absent evidence to to contrary, I'd sooner go with that than
speculation.

Plus Google and Wikipedia.


Yes whilst the 'stifness' of the tyre material modifies this
behaviour with pressure changes (for a fixed loading), the one thing
you _can_ guarantee is that the contact area will increase (up to a
limiting point -resting on the wheel rims) with reduction of inflation
pressure.
--
J B Good

On 03/02/15 16:51, Johny B Good wrote:
On Mon, 02 Feb 2015 15:40:26 +0000, Syd Rumpo
wrote:

On 02/02/2015 15:27, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
Radial ply tyres have a different construction to the tread area over
the sidewalls. Just how that reacts to varying pressure isn't a
constant. I'd say it is designed to give the correct 'footprint' at
the correct load/pressure. Altering either won't automatically give a
greater or lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same? I know where my money is - there's usually upwards of a quarter
of a tonne on each tyre.

If the tread 'belt' is made sort of concave, you might actually reduce the
contact area if you deflate from the correct pressure. Until the tyre is
nearly flat. In which case the 'grip' ain't going to matter much.

Well, I realise that the physics only applies fully to an idealised
tyre, but absent evidence to to contrary, I'd sooner go with that than
speculation.

Plus Google and Wikipedia.


Yes whilst the 'stifness' of the tyre material modifies this
behaviour with pressure changes (for a fixed loading), the one thing
you _can_ guarantee is that the contact area will increase (up to a
limiting point -resting on the wheel rims) with reduction of inflation
pressure.


I am not sure if yu or on fact other posters realise how trite what you
just said, is.

if each wheel e.g. is carrying a 500lb load, and its inflated to 25
psi, there will be exactly 20 square inches of tread in contact with the
rod, end of, unless the treads and sidewall are SO stiff that the
support is transmitted by other means than the tyre pressure itself.





--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Tue, 03 Feb 2015 17:05:20 +0000, The Natural Philosopher wrote:

Well, I realise that the physics only applies fully to an idealised
tyre, but absent evidence to to contrary, I'd sooner go with that than
speculation.

Yes whilst the 'stifness' of the tyre material modifies this
behaviour with pressure changes (for a fixed loading), the one thing
you _can_ guarantee is that the contact area will increase (up to a
limiting point -resting on the wheel rims) with reduction of inflation
pressure.

I am not sure if yu or on fact other posters realise how trite what you
just said, is.

if each wheel e.g. is carrying a 500lb load, and its inflated to 25
psi, there will be exactly 20 square inches of tread in contact with the
rod, end of, unless the treads and sidewall are SO stiff that the
support is transmitted by other means than the tyre pressure itself.

Everybody seems to be agreeing vehemently.

On 03/02/15 17:10, Adrian wrote:
On Tue, 03 Feb 2015 17:05:20 +0000, The Natural Philosopher wrote:

Well, I realise that the physics only applies fully to an idealised
tyre, but absent evidence to to contrary, I'd sooner go with that than
speculation.

Yes whilst the 'stifness' of the tyre material modifies this
behaviour with pressure changes (for a fixed loading), the one thing
you _can_ guarantee is that the contact area will increase (up to a
limiting point -resting on the wheel rims) with reduction of inflation
pressure.

I am not sure if yu or on fact other posters realise how trite what you
just said, is.

if each wheel e.g. is carrying a 500lb load, and its inflated to 25
psi, there will be exactly 20 square inches of tread in contact with the
rod, end of, unless the treads and sidewall are SO stiff that the
support is transmitted by other means than the tyre pressure itself.

Everybody seems to be agreeing vehemently.

My point being that it is in the intrinsic definition of 'pressure' and
I was surprised that anybody bothered to say it as if it were not.



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

In article ,
Syd Rumpo wrote:
Ok, I have physics, albeit idealised. I have links, here's one...

http://en.wikipedia.org/wiki/Contact_patch

'This article has multiple issues' They're right there.

...but you can use Google too. What do you have, religion?

--
*OK, so what's the speed of dark? *

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

On Saturday, 31 January 2015 17:57:36 UTC, Rod Speed wrote:

I'm not convinced that you do see less rubber in
contact with the asphalt with those two pressures.

You do. Ignoring the load taken by the side wall (which is usually
pretty trivial), formula is:
weight = pressure x contact-area

It really is that simple :-)

So for a given weight, increasing the tyre pressure, reduces the
contact area (and visa-versa).

so is the increased tyre wear at the lower pressure

Not convinced that that happens either.

proportional to the resulting greater contact area?

"Johny B Good" wrote in message
...
On Mon, 02 Feb 2015 15:40:26 +0000, Syd Rumpo
wrote:

On 02/02/2015 15:27, Dave Plowman (News) wrote:
In article ,
Syd Rumpo wrote:
Radial ply tyres have a different construction to the tread area over
the sidewalls. Just how that reacts to varying pressure isn't a
constant. I'd say it is designed to give the correct 'footprint' at
the correct load/pressure. Altering either won't automatically give a
greater or lesser contact area.

It's a good start. Three choices - if you deflate, within a sensible
range, will the contact area increase, decrease, or remain exactly the
same? I know where my money is - there's usually upwards of a quarter
of a tonne on each tyre.

If the tread 'belt' is made sort of concave, you might actually reduce
the
contact area if you deflate from the correct pressure. Until the tyre is
nearly flat. In which case the 'grip' ain't going to matter much.

Well, I realise that the physics only applies fully to an idealised
tyre, but absent evidence to to contrary, I'd sooner go with that than
speculation.

Plus Google and Wikipedia.


Yes whilst the 'stifness' of the tyre material modifies this
behaviour with pressure changes (for a fixed loading), the one thing
you _can_ guarantee is that the contact area will increase (up to a
limiting point -resting on the wheel rims) with reduction of inflation
pressure.

But that isn't relevant to the two pressures being discussed.

"Martin Bonner" wrote in message
...
On Saturday, 31 January 2015 17:57:36 UTC, Rod Speed wrote:

I'm not convinced that you do see less rubber in
contact with the asphalt with those two pressures.

You do. Ignoring the load taken by the side wall (which is usually
pretty trivial), formula is:
weight = pressure x contact-area

It really is that simple :-)

Fraid not in the sense we were discussing, whether the
increased pressure would see increased tyre wear.

So for a given weight, increasing the tyre pressure,
reduces the contact area (and visa-versa).

Its not that simple.

so is the increased tyre wear at the lower pressure

Not convinced that that happens either.

proportional to the resulting greater contact area?

On 03/02/2015 21:56, Rod Speed wrote:

snip

Fraid not in the sense we were discussing, whether the
increased pressure would see increased tyre wear.

No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area. You can read this yourself upthread.

Do you have to practise to be so wantonly stupid, or is it a gift?

Cheers
--
Syd

On 03/02/2015 22:43, Syd Rumpo wrote:
No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area.

What seems not to have been pointed out [1] is that total wear might not
be a critical issue. Lower inflation will tend to cause more wear
towards the edges of the tread; higher inflation towards the mid-point.

[1] I might well have missed it.

--
Rod

"Syd Rumpo" wrote in message
...
On 03/02/2015 21:56, Rod Speed wrote:

snip

Fraid not in the sense we were discussing, whether the
increased pressure would see increased tyre wear.

No, the suggestion was that lower pressure might result in more tyre wear
due to a greater contact area.

That was just ONE of the possibilitys being discussed.

The other was that the increased tyre pressure would
see the classic effect of wear in the center of the tyre.

You can read this yourself upthread.

You can too.

reams of your puerile attempt at insults any 2 year
old could leave for dead flushed where it belongs

On 03/02/2015 23:00, polygonum wrote:
On 03/02/2015 22:43, Syd Rumpo wrote:
No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area.

What seems not to have been pointed out [1] is that total wear might not
be a critical issue. Lower inflation will tend to cause more wear
towards the edges of the tread; higher inflation towards the mid-point.

[1] I might well have missed it.

The OP stated that, "...pressures were quoted - 29psi for 'comfort' and
36psi for 'eco'." I would take that to mean that distortions of the
wear pattern would not be significant within this range. If you were
to, for example, grossly overinflate, then you might obviously expect
that the tyre tread centre would wear more as it would be the part which
had most contact with the road.

My speculation was that, within the bounds set by the manufacturer, a
lower pressure might give more wear due to the larger contact area.

Cheers
--
Syd

On 04/02/2015 00:10, Syd Rumpo wrote:
On 03/02/2015 23:00, polygonum wrote:
On 03/02/2015 22:43, Syd Rumpo wrote:
No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area.

What seems not to have been pointed out [1] is that total wear might not
be a critical issue. Lower inflation will tend to cause more wear
towards the edges of the tread; higher inflation towards the mid-point.

[1] I might well have missed it.

The OP stated that, "...pressures were quoted - 29psi for 'comfort' and
36psi for 'eco'." I would take that to mean that distortions of the
wear pattern would not be significant within this range. If you were
to, for example, grossly overinflate, then you might obviously expect
that the tyre tread centre would wear more as it would be the part which
had most contact with the road.

My speculation was that, within the bounds set by the manufacturer, a
lower pressure might give more wear due to the larger contact area.

Those would be my assumptions. Modern tyres seem to wear more evenly,
even though they are now generally wider.

Perhaps they are circumferentially more stable?

On Wed, 04 Feb 2015 00:22:58 +0000, Fredxxx wrote:

Those would be my assumptions. Modern tyres seem to wear more evenly,
even though they are now generally wider.

Perhaps they are circumferentially more stable?

They tend to be much lower profile, so much stiffer sidewalls, so far
less flex and "tuck-under" on hard cornering.

In article ,
Fredxxx wrote:
My speculation was that, within the bounds set by the manufacturer, a
lower pressure might give more wear due to the larger contact area.

Those would be my assumptions. Modern tyres seem to wear more evenly,
even though they are now generally wider.

Perhaps they are circumferentially more stable?

The design of a modern tyre is extremely complex. It is not just a simple
rubber ring which will expand equally in all directions as pressure is
increased.

Which makes looking for some simplistic formula dealing with contact area
somewhat pointless.

--
*There are two kinds of pedestrians... the quick and the dead.

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

On 04/02/2015 10:19, Dave Plowman (News) wrote:

snip

The design of a modern tyre is extremely complex. It is not just a simple
rubber ring which will expand equally in all directions as pressure is
increased.

Which makes looking for some simplistic formula dealing with contact area
somewhat pointless.

So it's all just too complicated, we should leave it to the experts and
not worry our pretty little heads about it?

Cheers
--
Syd

On 03/02/15 22:43, Syd Rumpo wrote:
On 03/02/2015 21:56, Rod Speed wrote:

snip

Fraid not in the sense we were discussing, whether the
increased pressure would see increased tyre wear.

No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area. You can read this yourself upthread.


It doesn't actually work like that.

Since the greater area is suffering less force per unit area.

What incorrect tyre pressures do is put the wear unevenely over the tyre
tread - too high pressures wear the centre of the tread more as the tyre
bulges out to reduce the contact patch to that part of the tyre and too
low may cause the edges if the tread to wear as the inside part of the
tyre no longer is taking as much force as designed to.


Do you have to practise to be so wantonly stupid, or is it a gift?

Cheers

Well be careful. If any wear is unevenly distributed so that more of one
part of the tyre wears out ahead of the other part, then tyre LIFE -
being governed by the minimum tread on *any* part of the tread - will
suffer. From that point of view there is a best wear pressure and less
tyre life above *and* below it.



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 04/02/15 00:10, Syd Rumpo wrote:
On 03/02/2015 23:00, polygonum wrote:
On 03/02/2015 22:43, Syd Rumpo wrote:
No, the suggestion was that lower pressure might result in more tyre
wear due to a greater contact area.

What seems not to have been pointed out [1] is that total wear might not
be a critical issue. Lower inflation will tend to cause more wear
towards the edges of the tread; higher inflation towards the mid-point.

[1] I might well have missed it.

The OP stated that, "...pressures were quoted - 29psi for 'comfort' and
36psi for 'eco'." I would take that to mean that distortions of the
wear pattern would not be significant within this range. If you were
to, for example, grossly overinflate, then you might obviously expect
that the tyre tread centre would wear more as it would be the part which
had most contact with the road.


I've run tyres for long periods at that sort of deviation.

Mainly for cornering performance on my sports car youth. Wear does get a
bit more of the tyre centres when over inflated. But fuel consumption
perceptibly reduces as does ultimate grip.


My speculation was that, within the bounds set by the manufacturer, a
lower pressure might give more wear due to the larger contact area.

My experience suggests the higher pressure will wear the middles out.


All the useful things lie at high pressure - performance, roadholding an
economy, only one thing gets better at low pressure and that's traction
on soft surfaces (apart from 'comfort') so the likelihood is that the
'comfort' setting is the lowest pressure as can be got without too many
adverse effects.

And the eco setting will be on the other edge of the wear plateau.

Cheers


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 04/02/2015 10:41, The Natural Philosopher wrote:

snip

It doesn't actually work like that.

Since the greater area is suffering less force per unit area.

Yes, that must surely decrease the wear and I don't know how much it
would compensate for the extra contact area. I'm sure it won't exactly
balance.

What incorrect tyre pressures do is put the wear unevenely over the tyre
tread - too high pressures wear the centre of the tread more as the tyre
bulges out to reduce the contact patch to that part of the tyre and too
low may cause the edges if the tread to wear as the inside part of the
tyre no longer is taking as much force as designed to.

Agreed, but the OP wasn't talking about 'incorrect pressures' but a
range of pressures - 29psi (comfort) to 36psi (economy) as recommended
by the car manufacturer.

Cheers
--
Syd

On Wed, 04 Feb 2015 11:13:50 +0000, Syd Rumpo wrote:

Agreed, but the OP wasn't talking about 'incorrect pressures' but a
range of pressures - 29psi (comfort) to 36psi (economy) as recommended
by the car manufacturer.

And, as has been pointed out, that's a 24% increase in the tyre pressure,
taking it to very close to the maximum load pressure. It's not been set
for optimum tyre life, but for lowest rolling resistance and thereby fuel
economy. A quick google finds that payload for a Zafira can be nearly 45%
of the empty weight, so the difference between max laden and unloaded is
substantial.

http://carleasingmadesimple.com/busi...uxhall/zafira-
diesel-tourer/54064/technical-data/
GVW 2410kg, payload 725kg, giving ULW 1685kg.

On Wed, 04 Feb 2015 10:48:17 +0000, The Natural Philosopher wrote:

I've run tyres for long periods at that sort of deviation.

Mainly for cornering performance on my sports car youth. Wear does get a
bit more of the tyre centres when over inflated. But fuel consumption
perceptibly reduces as does ultimate grip.

Somehow, I doubt the reduced fuel economy in those circumstances was due
to the tyre pressures...

On 04/02/15 11:13, Syd Rumpo wrote:
On 04/02/2015 10:41, The Natural Philosopher wrote:

snip

It doesn't actually work like that.

Since the greater area is suffering less force per unit area.

Yes, that must surely decrease the wear and I don't know how much it
would compensate for the extra contact area. I'm sure it won't exactly
balance.

What incorrect tyre pressures do is put the wear unevenely over the tyre
tread - too high pressures wear the centre of the tread more as the tyre
bulges out to reduce the contact patch to that part of the tyre and too
low may cause the edges if the tread to wear as the inside part of the
tyre no longer is taking as much force as designed to.

Agreed, but the OP wasn't talking about 'incorrect pressures' but a
range of pressures - 29psi (comfort) to 36psi (economy) as recommended
by the car manufacturer.


'incorrect' is a matter of hand waving definition.

A tyre is designed for a reasonable compromise at a given contact area.
The pressure depends on how much load the tyre is taking to achieve that
contact area.

Wear, ride comfort, grip, noise and fuel economy are all parameters that
can be optimised over a reasonable range of contact patches around a
broad optimum. Its not necessarily clear that those will all be optimum
at a given contact patch area and in fact they are not.

Nor are they preserved across tyre manufacturers and alternative products.

I have had tyres last as little as 6000 miles (cheap Mini tyre driven
hard) and as much as 60,000 miles (Land Rover hard all terrain tyre
driven sensibly).

They both wore evenly.

In short, beware of simple answers to complex questions.

Cheers


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 04/02/15 11:19, Adrian wrote:
On Wed, 04 Feb 2015 10:48:17 +0000, The Natural Philosopher wrote:

I've run tyres for long periods at that sort of deviation.

Mainly for cornering performance on my sports car youth. Wear does get a
bit more of the tyre centres when over inflated. But fuel consumption
perceptibly reduces as does ultimate grip.

Somehow, I doubt the reduced fuel economy in those circumstances was due
to the tyre pressures...

It most certainly was.


You can by going to rock hard tyres get maybe 30% less rolling
resistance at low speeds.

As any cyclist will tell you.

Once aerodynamic drag takes over - generally 50mph - as the dominant
losses, its less of an issue.

Rolling resistance is the single largest frictional force a car
experiences at lower speeds. (excluding sticking the brakes on).
Transmission and engine friction are much lower in general though still
significant.

If you want real eco, use bicycle type tyres on uber narrow rims with
very very high pressure. And very very low contact patch areas. Juts
dont expect to get ant traction or cornering performance.



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 04/02/2015 12:41, The Natural Philosopher wrote:

snip

In short, beware of simple answers to complex questions.

Actually, the question was simple.

I don't get this. There is a relationship between tyre pressure, load
and contact area based on some initial simplifications - that's usually
how science works. But instead of using that as a starting point, we
get wise men with their personal anecdotes telling us that it's all too
complicated.

I mean, really. What a load of pompous ********.

Cheers
--
Syd

In article ,
Syd Rumpo wrote:
On 04/02/2015 10:19, Dave Plowman (News) wrote:

snip

The design of a modern tyre is extremely complex. It is not just a
simple rubber ring which will expand equally in all directions as
pressure is increased.

Which makes looking for some simplistic formula dealing with contact
area somewhat pointless.

So it's all just too complicated, we should leave it to the experts and
not worry our pretty little heads about it?

In your case, yes. ;-)

--
*I'm not a paranoid, deranged millionaire. Dammit, I'm a billionaire.

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