Nigel Hi,
please do not worry. Maths and physics was not my very best point either but
I will try to give an example based on my cars.
One of them is a fully kitted out genuine camel trophy Discovery 200Tdi in
100% genuine condition and fitted with the 7.00 X 16" Michelin XZL tyres
that were original fitment for the 1994 event that it participated in as the
Greek team vehicle. This type of vehicle had a weight of around 2.800 kilos
when fitted with all the kit and additional fuel and water so with the
equipment that can not removed (roofrack, skid plates front and rear,
bullbar, rollcage, Husky winch, three tow hooks the estimated weight with
the driver is around 2.500 kilos.
The second one is another camel trophy Discovery but I have now removed the
roofrack, bullbar and winch still retaining the rollcage and having added
A/C and replacing the manual gearbox and LT230 transfer box with an autobox
and Borg Warner transfer box. I calculate its weight to around 2.200 kilos.
It is now fitted with KUMHO 205 X 16" tyres
--------------------------------------------
Factory suggested tyre pressure for ordinary specifications Discovery
vehicles (200Tdi) is 1.9 psi for the front wheels and 2.6 psi for the rear
wheels for a vehicle that weights around 2.000 kilos so let's take this an a
basis for our example.
My tyre fitter (who is also a good personal friend) has suggested I use 2.1
psi (30 bars) and 2.8 psi (40 bars) respectively front and rear and this is
what I have been using for the last 10 years of accumulated CT Discos
ownership.
------------
Now back to the maths of the formula for an ordinary Discovery and then for
the CT (it is a good opportunity to check it anyway)
An ordinary Discovery 200Tdi, 5 door with A/C weights 2.095 kilos (this is
factory quoted weight from the Land Rover Experience book, second edition
October 1994)
2.095 kilos is around 4.170 lbs (please correct me if I am wrong but I was
only able to find pounds as weight. A pound is similar to 1 lbs?)
So A = 4.170 lbs (please confirm)
Side wall maximum weight as quoted on the KUMHO tyres is 1984 lbs multiplied
by 4 = 7.936 lbs
So B = 7.936 lbs
B into A = 1,903
Therefore C = 1,903
Side wall maximum pressure for the KUMHO tyres is 44 psi.
Therefore D = 44
C into D = (44/1,903) = 23
Therefore suggested tyre pressure must be 23 psi (or 1.6 bars) for the
KUMHO tyres.
------------
If we apply the same formula for the heavier vehicle with the XZL Michelin
tyres the outcome should be
A = vehicle's weight = 2.500 kilos = 5.510 lbs (I presume a pound is the
same as lb)
B = sidewall maximum weight X 4 = 2205 lbs X 4 = 8.820 lbs
C = A/B = 5.510/2.205 = 2,498
D = sidewall maximum pressure = 65 psi
Suggested tyre pressure must be D/C = 65/2,498 = 26 psi (or 1.8 bars)
--------------------
This sounds a bit low on both occasions but I hope the example was useful.
Take care
Pantelis
Recommended factory tyres pressure, as already quoted, is 1.9 and 2.6 psi
(28 and 38 bars for those who prefer this system)
"Nigel Hewitt" <
[email protected]> wrote in message
news:
[email protected]...
> Pantelis Giamarellos wrote:
>
> > Truck weight in lb's =A
> > Side wall max weight x 4 =B
> > B into A = C
> > Side wall max pressure =D
> > C into D = ideal psi.
>
> OK. I am a bear of very little brain but I'm not even sure I understand
the
> items let alone the concepts. Can somebody explain in words of one
> syllable what this means? An example, including where I get the numbers
> from, would be magic.
>
> nigelH
>
>
