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As per my previous query, I now have an Autotrail Tracker FB which is 4 years old and has 8700 miles on the clock.

I bought it from a firm in Nottingham who told me to ignore the Tyre Pressure plate inside the cab door and they had inflated all the tyres to 65PSI as this was adequate.

The vehicle is rated at 3650KG

I decided to take a further look at this as the plate on the cab door and the Autotrail owners manual suggests that the tyres be inflated to 72PSI front and 79PSI rear.

I went down to the local garage to adjust the tyre pressures accordingly but was surprised to see that on the tyre wall a maximum pressure rate as 69PSI on three tyres an 5.5Bar on the fourth.

All the tyres are Continental Vanco Camper tyres

Three are  215/70 CP 109R (69PSI)

One is 215/70 CP 100R (5.5Bar)

I rang Autotrail and they insist that despite the tyre wall maximum rating, all should be inflated to 79PSI - 5.5BAR  They suggest the odd tyre may have been a replacement tyre possible due to a blow out or puncture and could be replaced to match the others.

Help!  Do I need to change the tyre pressures?  Do I need to change the odd tyre to match the others?

In the mean time, I have inflated all the tyres to 69PSI (4.75BAR)

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I do feel a fool.

 

I have been back out to re-examine the tyres and the one I thought was load rating 100 was in fact 109.  I was reading it upside down (my excuse anyway)

All the tyres say 69PSI but further round there is a Maximum Pressure of 5.5BAR rating so everything is alright and I can go ahead and inflate the tyres as instructed by AUTOTRAIL.

 

Must get my glasses cleaned some time soon!

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Although I see this is an older topic, I can add information that will solve your confusion.

 

Continental is , I think , the only tyremaker who gives on his CP tyres  and the pressure needed for the maximum load  up to 160km/99m/h, wich is called the reference-pressure and is meanth cold measured at 18 degr C /65 degr F.   Cold is simply when inside tyre temp = outside tire temp.

But also  gives maximum allowed cold pressure  wich is higher .

Yust like a normal car tyre gives only maxcold on sidewall but referenceopressure is standard 36 psi/2.5 bar for standard load and 42psi/2.9bar for XL/reinforced /Extraload.  They give between 44psi/3bar and 51psi /3.5bar on sidewall as maxcold and for XL sometimes up to 60psi/4.2bar.

Michelin gives on his CP tires only maxcold of 80 psi and sometimes gives it even as  AT 80 psi  apart from the maximum load.

So you see that the system is not always that consequently used .

After AT in for instance " maximum load 1030kg AT 69 psi "  is the referencepressure, and maxpressure or maximum cold pressure given is the maximum allowed cold pressure.

 

When the tire inside air heats up by driving, the pressure rises and this is included in the cold advice.

Once read that tyres are tested to can stand a 2 to 3 times the AT-pressure ( as I will call reference pressure furtheron).

Even when you would fill your tyres at freesing point of water so 0 degr C /32 degr F) with 40% higher pressure then AT, so your case 69 x 1.4=97 psi , and the temp inside the tire would reach boiling point of water , so 100 degr C/212 degr F,  the pressure would rise to about 2 times AT so about 138 psi, wich it than still can stand without blowing , if the tire is not damaged by onderinflation or overloading so overheating.

 

Also saw on Viking tyres both pressures given, though they where not CP tyres.

So AT-pressure is what you need to calculate the pressure needed, and maxcold is only what the tyremaker allowes as cold pressure ( for responcibility reasons) , mother nature allows even higher.

 

Greatings from a "pigheaded Dutch selfdeclared tyrepressure-specialist

Peter

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