Tyre Pressures 110 CSW

In article , Wolverine writes

Mine are 40/42 psi (Goodyear Wranglers)

Regards,

Simonm.

On or around Thu, 13 Oct 2005 11:40:31 +0100, "Wolverine" enlightened us thusly:

arrrgrh, not again.

I'd go for about 36 all round, but tyhe book will tell you 28 front 42 rear or somesuch. 28 is too soft for good tyre wear although it probably makes for a slightly smoother ride. 36 is fine in the back provided you're not carrying heavy weight, in which case you need to up them to 40 maybe.

the 28 figure dates back to cross-ply tyres - radials, size-for-size, seem to run better a bit harder.

BFG AT at 28 35 that lasted 50k is that good or bad ??

Isnt there a formula to calculate pressure; saw one years ago byt cant trace it ??

(snip)

Don't think there can be a general formula - all tyre pressures are a compromise, comfort and ground pressure on the side of low pressure, tyre life and handling on the side of high pressure, with added complications of needing to increase rear pressure as load increases. Having the pressures wrong between front and back can make a big difference to handling.

Placarded pressures on my 110 are 35/35 unloaded at speeds below 100kph up to 65/60 fully loaded at sustained speeds above 120kph. And take off 15 for soft ground. (all in psi) Note that these pressures are all higher than the UK recommended pressures, probably because Australians drive long distances at high speed in high temperatures on rough roads. JD

Fellow listers,

took me some time to unearth the formula but finally managed to find it.

QUOTE

1. Take the total weight of your truck, write it down and put an "A" next to it.
2. Then multiply the maximum weight from the tyre sidewall by four {four tyres under the truck}, write down the answer and but a "B" next to it.
3. Divide "A" into "B" and write the number down with a "C" next to it.
4. Next divide "C" into the maximum side wall pressure "D", and you have the correct pressure for your tyres on your truck.

--------------------- The formula is shown again below to help.

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.

With the correct inflation pressure and having been balanced right, your new tyres will give years of faithful service.

UNQUOTE.

Unfortunately I have not noted from where I have copied it but whoever has posted it first is to be thanked. Works very nicely but will work even better if you do it on an per vehicle's axle basis. So you calculate the front axle's weight as A and multiply by 2 (instead of 4) in order to calculate variant B.

You see our landies tend to be more nose heavy, especially if they are fitted with winches, bullbars etc.

Take care and hope this helps. Pantelis

Nice theory - and it doesn't work.

Sorry but that was all I had in relation to tyre pressure formulae.

Take care Pantelis

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

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)

On or around Sat, 15 Oct 2005 11:22:52 +0300, "Pantelis Giamarellos" enlightened us thusly:

pedantic, I know, but you've got yer psi and bar on backwards.

Mind you, if the tyres could take it, he could float all the way from Greece on those tyres at that psi!!

;~)

Nige

-- Subaru WRX Landrover 110 County Station Wagon (Tyson) WTB a clean RRC pref 3.9 or LSE 4.2

'"gimme the f*ckin' money"

You must be right.

What I use is the bigger numbers 'cause I tend to remember them more easily (30/40)

Take care Pantelis

LOL !!!!

Take care Pantelis

Greece on those tyres at that psi!!