Tyre Pressures

[AnnM1]

Can anyone explain to me why there is such a great variation in caravan tyre psi?

For the Dawnstar and Brightstar it states in the technical specification that the psi should be 42. Yet similar sizes vans psi are quoted as high as 60.

Thanks for any clarification you can throw on this.

 

[Lutz]

It all depends on the tyre size. Both tyre size and tyre load determine the pressure.

 

[mcghee]

The determining factor is the weight to be carried by the tyre. the more weight you put on a tyre the more the sidewall compresses, and this leads to heat build up in the tyre carcass and eventually tyre failure. it is equally important not to over inflate your tyres as this will have a similar effect, but on the centre of the tread area rather than the sidewall.

 

[RogerL]

There are four different types of radial tyre construction, in respect of cars and caravans - normal, reinforced, 6-ply and 8-ply. The different constructions allow different maximum pressures and therefore different load limits.

All tyres have size, speed and load ratings moulded into their sidewalls. The construction is often given, in small print, but in any case is taken into account in the Load Index.

For caravanners, it's not as simple as quoting a tyre size, the load rating also has to be quoted.

My caravan came fitted with 165/80 R13 8-ply tyres with a load index of 94 and a maximum pressure of 65psi. When they needed replacement I fitted 175/80 R13 6-ply which also have a load index of 94 but a maximum pressure of 54psi.

Caravan manufacturers changed from 13" to 14" wheels/tyres in '00-'02. The larger tyres used recently can often be specified at "lower" levels of construction and therefore may well have lower recommended pressures than earlier models of the same size and weight.

 

[gary]

There are essentially four different types of tyre fitted to caravan. The first is what we commonly refer to as 'car tyres', these are most often fitted on twin axles or on lightweight single axle vans due to their limited weight carrying capacity.

Next up are 'light commercial' tyres either 6ply or 8ply instead of the 4plys of 'car tyres'.

Generally speaking all these tyres carry increased weight at increased pressure in a linear fashion, from about 340kg for a 4ply to 750kg for the 8ply at pressures from 35 to 65psi.

The fourth type is known as 'reinforced', this type does not follow the same weight to pressure ratio as the first three and has a ratio all it's own.

Where as the first three would have roughly the same pressure for a given weight, the reinforced needs considerable less pressure at that same given weight.

All this information is written on the side wall of the tyre, there is a weight index number or more useful is the American system which gives max weight at a max pressure. These figures given you know the weight of your van can then be used to calculate the correct pressure for the tyres fitted.