Ronzo wrote:

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Fellow travellers

I have a Pajero Sport 2021 AWD

I tow a New Age Mantaray 2015 model approx wt 2200 tonnes loaded

The Mitsubishi manual says when towing Front tyre pressure should be 29 and back 36 psi 

I had a recent discussion with a NAge repairer and he suggested pressure should be up around 50psi

Your opinions please

Thanks & regards

Ronzo

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Don't have access to figures for your car, but I run 2300kg on car's rear axle at 52-55 psi on good roads. Your suggested 50psi seems stupidly high, but I can't presently access my figures for your car . Maybe tomorrow. Cheers

 

I'm sure someone here will give you an answer.  Sorry but my advanced editor still doesn't work properly so you will need to copy and paste.

 

https://www.pajeroforum.com.au/forum/vehicles/pajero-sport-qf-2019

Hi John, I think you were querying Whenarewetherenow's pressure from the sunny side to the other. I noticed that occuring at Toowoomba at a relative's place with the "cold" temperatures being different when the sun has warmed up the tyres exposed to the sun.

I guess that brings up a question - what is the cold temperature to use for a reference?
My cold temperature in my garage here in Townsville now is 24 degrees. Yours might be 15 or less. Tyres certainly have a lot to put up with - some people ignore them until they find their fuel use goes up.

I have a Mitsubishi Challenger with16" rims and 160kg towball wt and run 40 psi rear and 35 psi front. In my opinion 50 psi is too high.

Any advice given, unless they have the "exact same car, exact same tyres, exact same van and exact same weights, should be ignored as not only wrong but dangerous advice.

The answers you seek is and has been for over 40 years as required by law, embossed onto the sidewall of your tyres.

The tyre placard data affixed to your car and van only applies to the original vehicle as it left the production line.

It is essentially useless information, but some obscure law introduced back in 1989 when ADRs first came out requires it.

Unfortunately, as soon as you change anything, weights, tyres, etc, then it no longer applies.

 

Because weights are so important, every truckie is taught the simple formula that is on your tyre side wall, and it requires only simple primary school math.

 

Your tyre will say XXX PSI at XXXkg. This is the manufacturers recommendations and should not be varied.

More weight = more PSI, less weight equals less PSI.

The math is: real weight divided by maximum weight times the pressure.

 

The same formula is used for your caravan as it is on your car.

Lets ignore the maximum weight the vehicle manufacturer allows for the moment because that's a whole different kettle of fish.

 

Lets use my Yokohama Geolandar GO15 tyres fitted to my car as an example. They say max 51PSI at 1050kg.

As I have two rear tyres, at the maximum weight of 2100kg load on those rear tyres I should inflate the tyres to 51PSI.

If the load was 1850kg the math is as follows:-

(1850/2100) x 51

= 0.8809 x 51

= 44.9PSI

Simples! So I inflate my rears when towing to 45PSI

When not towing there is about 3000kg less load (towbar load and gear in the back like car fridge etc) so the formula is (1550/2100) x 51 =37.64PSI, so I inflate to 38PSI.

 

My fully loaded van weighs in at 2800kg and I have only two tyres (Toyo) that state 80PSI at 1550kg (2x1550=3100kg).

The towball weight is 250kg so that means 2550kg on those two wheels.

The math is as follows:

(2550/3100) x 80

= 0.8225 x 80

= 65.8PSI

 

Simples!

 

If my van was a tandem, ie., 4 tyres, I wouldn't have such heavy duty 1550kg capacity tyres, but the math would be as follows:

(2550/6200) x 80

=0.4112 x 80

= 32.9PSI

 

Simples!

 

The lovely folks at G&S Chassis (now ALKO) have a calculator on their web site if the basic math is too much for some folks.

http://www.gnschassis.com.au/tyre-pressure-calculator/

-- Edited by Hylife on Tuesday 22nd of November 2022 09:43:33 PM