Calculating tyre pressure ?

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H

Hirsty's

Guest
Old chestnut again, I have no definitive idea of tyre pressure for my 110;
however I did find a site that showed how to calculate it.
Along the lines of ............ take max load for tyre and max pressure,
then calculate pro rata the presure needed due to actual axle weight at the
wheel in question.
Anybody know if this has any substance, after all someone must calculate for
manufacturers recomended pressures

John H

--


" ..... it is the provenence of knowledge to speak, and it is the privelage
of wisdom to listen"


 
Hirsty's wrote:

> Old chestnut again, I have no definitive idea of tyre pressure for my
> 110; however I did find a site that showed how to calculate it.
> Along the lines of ............ take max load for tyre and max pressure,
> then calculate pro rata the presure needed due to actual axle weight at
> the wheel in question.
> Anybody know if this has any substance, after all someone must calculate
> for manufacturers recomended pressures
>
> John H
>

This will calculate a pressure based solely on the tyre manufacturer's ideas
of what their tyres will stand. It will probably give a higher pressure
than you really want - I'm also not sure that pro rata is the way to go
either.

Tyre pressures as recommended by the manufacturer are not calculated - they
are worked out by trial and error during testing and are a compromise
between comfort, handling and tyre life. Too low compromises tyre life and
usually handling, too high will sacrifice ride comfort and often handling.
JD
 
On or around Wed, 16 Aug 2006 07:11:36 +1000, JD <[email protected]>
enlightened us thusly:

>Hirsty's wrote:
>
>> Old chestnut again, I have no definitive idea of tyre pressure for my
>> 110; however I did find a site that showed how to calculate it.
>> Along the lines of ............ take max load for tyre and max pressure,
>> then calculate pro rata the presure needed due to actual axle weight at
>> the wheel in question.
>> Anybody know if this has any substance, after all someone must calculate
>> for manufacturers recomended pressures
>>
>> John H
>>
>
>This will calculate a pressure based solely on the tyre manufacturer's ideas
>of what their tyres will stand. It will probably give a higher pressure
>than you really want - I'm also not sure that pro rata is the way to go
>either.
>
>Tyre pressures as recommended by the manufacturer are not calculated - they
>are worked out by trial and error during testing and are a compromise
>between comfort, handling and tyre life. Too low compromises tyre life and
>usually handling, too high will sacrifice ride comfort and often handling.

although quite a lot of LR products seem to run nicer with a bit more in the
front tyres. ride quality is reduced a bit but tyre wear, handling and
economy all get a touch better.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"The great masses of the people ... will more easily fall victims to
a great lie than to a small one" Adolf Hitler (1889 - 1945)
from Mein Kampf, Ch 10
 


>
> Tyre pressures as recommended by the manufacturer are not calculated -
they
> are worked out by trial and error during testing and are a compromise
> between comfort, handling and tyre life. Too low compromises tyre life and
> usually handling, too high will sacrifice ride comfort and often handling.
> JD

Trouble is LR dont give figures for 235 85 16's on a 110 and they dont know
what they should be ( I phoned them )


 

"Hirsty's" <[email protected]> wrote in message
news:[email protected]...
>
>
>>
>> Tyre pressures as recommended by the manufacturer are not calculated -
> they
>> are worked out by trial and error during testing and are a compromise
>> between comfort, handling and tyre life. Too low compromises tyre life
>> and
>> usually handling, too high will sacrifice ride comfort and often
>> handling.
>> JD
>
> Trouble is LR dont give figures for 235 85 16's on a 110 and they dont
> know
> what they should be ( I phoned them )
>
you could run on the pressure for the narrower tyre 225 ? this will give
that slight increase that most of us seem to run and adjust to taste if you
find it too firm or notice increased wear in the centre (unlikely IMO). or
Dunlops recommendation 1.9bar 28 psi (F) 2.4 bar 35psi (R) load index
104-116 (dunno what that is )
http://www.dunloptyres.co.uk/fandp/vehicleSearch/result/?vehicleId=B2CZD
Derek


 
Hirsty's wrote:

>
>
>>
>> Tyre pressures as recommended by the manufacturer are not calculated -
> they
>> are worked out by trial and error during testing and are a compromise
>> between comfort, handling and tyre life. Too low compromises tyre life
>> and usually handling, too high will sacrifice ride comfort and often
>> handling. JD
>
> Trouble is LR dont give figures for 235 85 16's on a 110 and they dont
> know what they should be ( I phoned them )

"Contrary to popular belief, tyre pressure is not determined by the type of
tyre or its size but
upon your vehicle's load and driving application i.e. speed"

quoted from
http://www.bridgestone.com.au/tyres/products/car/care/pressure.asp

And these people make the tyres!
JD
 


> you could run on the pressure for the narrower tyre 225 ? this will give
> that slight increase that most of us seem to run and adjust to taste if
you
> find it too firm or notice increased wear in the centre (unlikely IMO). or
> Dunlops recommendation 1.9bar 28 psi (F) 2.4 bar 35psi (R) load index

This is exactly what I have always run them at, but I am intrigued to know
the collective wisdom and the "correct" pressure


 
JD wrote:

> "Contrary to popular belief, tyre pressure is not determined by the type of
> tyre or its size but
> upon your vehicle's load and driving application i.e. speed"

Yep. And most vehicle manufacturers quote pressures that are too low in
the interests of less road noise and better ride. The whole
Bridgestone/Ford SUV debacle in the US stemmed from this combined with a
less than optimally made tyre.

Another change that complicates things is that a lot of vehicle
manufacturers are still remembering the days of cross ply tyres which
had a much stiffer carcass and thus needed less pressure to handle well
and stay cool in use - many of the designers don't seem to have grasped
this change.

I saw a new set of pressure charts from one of the large tyre
manufacturers (can't remember which one) a few weeks ago that was
showing pressures about 15% higher across their entire size range than
any similar charts I have seen in the past - so there may be a bit of
realism creeping in to the industry.

I've fitted/sold tyres for most of the last 20 years (until I left the
automotive industry) and somewhere between 10 and 20% greater pressure
than the vehicle manufacturers suggestion is a good rule of thumb. As
an example my wife's car is running 34/32psi front/rear (as opposed to
the 29/27 on the placard) and after 50,000km the tyres are worn
perfectly evenly. The cornering is a lot sharper and it runs more
nicely on cambered roads. The only downside is a noticeable increase in
road noise.

IMO (from experience with my own vehicles) 235/85R16's are happy with
about 32 to 34 psi all round if you're not heavily laden. Give these
pressures a try and see what you think of it's stability and cornering.


--
EMB
 
EMB wrote:

> JD wrote:
>
>> "Contrary to popular belief, tyre pressure is not determined by the type
>> of tyre or its size but
>> upon your vehicle's load and driving application i.e. speed"
>
> Yep. And most vehicle manufacturers quote pressures that are too low in
> the interests of less road noise and better ride. The whole
> Bridgestone/Ford SUV debacle in the US stemmed from this combined with a
> less than optimally made tyre.
>
> Another change that complicates things is that a lot of vehicle
> manufacturers are still remembering the days of cross ply tyres which
> had a much stiffer carcass and thus needed less pressure to handle well
> and stay cool in use - many of the designers don't seem to have grasped
> this change.
>
> I saw a new set of pressure charts from one of the large tyre
> manufacturers (can't remember which one) a few weeks ago that was
> showing pressures about 15% higher across their entire size range than
> any similar charts I have seen in the past - so there may be a bit of
> realism creeping in to the industry.
>
> I've fitted/sold tyres for most of the last 20 years (until I left the
> automotive industry) and somewhere between 10 and 20% greater pressure
> than the vehicle manufacturers suggestion is a good rule of thumb. As
> an example my wife's car is running 34/32psi front/rear (as opposed to
> the 29/27 on the placard) and after 50,000km the tyres are worn
> perfectly evenly. The cornering is a lot sharper and it runs more
> nicely on cambered roads. The only downside is a noticeable increase in
> road noise.
>
> IMO (from experience with my own vehicles) 235/85R16's are happy with
> about 32 to 34 psi all round if you're not heavily laden. Give these
> pressures a try and see what you think of it's stability and cornering.
>
>

An interesting comment on this is that my 110 has an Australian Supplement
to the owner's handbook. As well as covering special local variations such
as different engines in some models, it tells you to ignore the tyre
pressure recommendations in the owner's handbook and provides a new table,
which is copied on the vehicle placard. This lists pressures well above the
originals, minimum of 35/35 unloaded at speeds up to 100kph, going up to
60/65 at maximum weight and speeds over 120kph. Tyres type and size
specified is the same as in the UK handbook. And this was in 1986.
JD
 
Hi,

Is there any chance of getting a scan or details of the tyre pressure
chart you mention, it would be very useful for us all I think,

Thanks, Andrew

(1986 110 V8)


JD wrote:
>
> An interesting comment on this is that my 110 has an Australian Supplement
> to the owner's handbook. As well as covering special local variations such
> as different engines in some models, it tells you to ignore the tyre
> pressure recommendations in the owner's handbook and provides a new table,
> which is copied on the vehicle placard. This lists pressures well above the
> originals, minimum of 35/35 unloaded at speeds up to 100kph, going up to
> 60/65 at maximum weight and speeds over 120kph. Tyres type and size
> specified is the same as in the UK handbook. And this was in 1986.
> JD

 
Andrew T. wrote:

> Hi,
>
> Is there any chance of getting a scan or details of the tyre pressure
> chart you mention, it would be very useful for us all I think,
>
> Thanks, Andrew
>
> (1986 110 V8)
>

Tyre pressures from Owners manual Australian Supplement Part No TP 1107 A
for Landrover 110 dated 2/85

Load Up to 105kph 105-120 Over 120

up to 0.5 Tonne 35/35 45/45 50/50
0.5 to 1.0 35/45 47/55 55/62
Over 1.0tonne 40/50 50/60 60/65

Pressures may be reduced by 4psi for crossply tyres

Presure may be reduced by 15psi for limited cross country operation.

I have not given the pressures for the 6x6 as these are rare outside
Australia (and pretty rare here too!) and have only given pressures in psi.

Hope this helps
JD
 
Thanks alot! - as you say they are consistantly higher than "normal"
recommendations.

Next problem is trying to find an accurate but not silly money pressure
gauge.

Cheers, Andrew


JD wrote:
>
> Tyre pressures from Owners manual Australian Supplement Part No TP 1107 A
> for Landrover 110 dated 2/85
>
> Load Up to 105kph 105-120 Over 120
>
> up to 0.5 Tonne 35/35 45/45 50/50
> 0.5 to 1.0 35/45 47/55 55/62
> Over 1.0tonne 40/50 50/60 60/65
>
> Pressures may be reduced by 4psi for crossply tyres
>
> Presure may be reduced by 15psi for limited cross country operation.
>
> I have not given the pressures for the 6x6 as these are rare outside
> Australia (and pretty rare here too!) and have only given pressures in psi.
>
> Hope this helps
> JD

 
JD wrote:
> Hirsty's wrote:
>
>> Old chestnut again, I have no definitive idea of tyre pressure for
>> my 110; however I did find a site that showed how to calculate it.
>> Along the lines of ............ take max load for tyre and max
>> pressure, then calculate pro rata the presure needed due to actual
>> axle weight at the wheel in question.
>> Anybody know if this has any substance, after all someone must
>> calculate for manufacturers recomended pressures
>>
>> John H
>>
>
> This will calculate a pressure based solely on the tyre
> manufacturer's ideas of what their tyres will stand. It will probably
> give a higher pressure than you really want - I'm also not sure that
> pro rata is the way to go either.
>
> Tyre pressures as recommended by the manufacturer are not calculated
> - they are worked out by trial and error during testing and are a
> compromise between comfort, handling and tyre life. Too low
> compromises tyre life and usually handling, too high will sacrifice
> ride comfort and often handling. JD

Seem to recall there's some law/ruling that tyres must be inflated within
2lb/in^2 of the manf recommended.

--
If Your specification is vague or imprecise, you'll likely get what you
asked for not what you wanted!

Do not say it cannot be done, rather what is needed for it to be done!


 
For what its worth, I run a 200TDi 90 on crossply Mud Pluggas (SAT
clone). As a main use of the vehicle is RTV trials I leave the tyre
pressures at 25psi all round as this gives me a margin over the 22 psi
min pressure for trials. I have no problems with road holding or tyre
wear. They are wearing evenly and look like they will probably do
around 20,000 miles before they're road illegal, not that they'll be
much good off road by then. The only problem is the noise (no carpets
or other sound proofing) and the feeling of running over bricks at slow
speeds. They towed the caravan up to the Nationals and down to Newnham
at 60, competed, then home again all at the same pressure, no trouble.

Gordon

 
On or around 16 Aug 2006 04:22:43 -0700, "gordon" <[email protected]>
enlightened us thusly:

>For what its worth, I run a 200TDi 90 on crossply Mud Pluggas (SAT
>clone). As a main use of the vehicle is RTV trials I leave the tyre
>pressures at 25psi all round as this gives me a margin over the 22 psi
>min pressure for trials. I have no problems with road holding or tyre
>wear. They are wearing evenly and look like they will probably do
>around 20,000 miles before they're road illegal, not that they'll be
>much good off road by then. The only problem is the noise (no carpets
>or other sound proofing) and the feeling of running over bricks at slow
>speeds. They towed the caravan up to the Nationals and down to Newnham
>at 60, competed, then home again all at the same pressure, no trouble.

I imagine that's about right for a 90 on oversize crossplies, I'm assuming
that you're on 7.50s... crossplies work at lower pressures.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Nessun maggior dolore che ricordarsi del tempo felice nella miseria"
- Dante Alighieri (1265 - 1321) from Divina Commedia 'Inferno'
 

"JD" <[email protected]> wrote in message
news:[email protected]...
> Hirsty's wrote:
>
>>
>>
>>>
>>> Tyre pressures as recommended by the manufacturer are not calculated -
>> they
>>> are worked out by trial and error during testing and are a compromise
>>> between comfort, handling and tyre life. Too low compromises tyre life
>>> and usually handling, too high will sacrifice ride comfort and often
>>> handling. JD
>>
>> Trouble is LR dont give figures for 235 85 16's on a 110 and they dont
>> know what they should be ( I phoned them )
>
> "Contrary to popular belief, tyre pressure is not determined by the type
> of
> tyre or its size but
> upon your vehicle's load and driving application i.e. speed"
>
> quoted from
> http://www.bridgestone.com.au/tyres/products/car/care/pressure.asp
>
> And these people make the tyres!
> JD

Yep and they also are responsible for this
http://cbs4boston.com/recalls/recalls_story_203005816.html
which sort of explains how much they actually know
Derek


 
gordon wrote:
> For what its worth, I run a 200TDi 90 on crossply Mud Pluggas (SAT
> clone). As a main use of the vehicle is RTV trials I leave the tyre
> pressures at 25psi all round as this gives me a margin over the 22 psi
> min pressure for trials. I have no problems with road holding or tyre
> wear.

I often have a set of 7.50x16 SATs on my SIIa - I find that raising the
fronts to about 28psi significantly improves the steering response on-road.


--
EMB
 
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