The motorhome came shipped with tyre pressure at 5.5bar (80psi) Check with Continental techsupport. 225/75 R16 116R Vanco Camper. On Fiat alloy wheels.
Fiat garages I contacted said they could not do anything and the Fiat Pro people in Italy just passed the information to the technical department.
As a follow up Nov 18.
I took the van to a tyre dealer and he found the settings but was unable to change them. He sent me to an auto electrical workshop. They checked and said the setting could be changed to 4 Bar (58psi) on the front and 4.5 bar (65psi) on the back and charged £60. The have been fine for 3800 miles so far and the ride is much better.
The reply came back from continental
It is extremely likely that the relevant information supplied with the chassis is documented for use as a commercial vehicle, therefore proposed before the conversion to a motor home. For this reason, Continental tyres would always recommend having the motor home weighed on a weigh bridge at your heaviest travelling weight, including liquids to achieve specific axle weights. In some cases the coach builder will also put their recommended pressures on the vehicle plate. However, the majority put this to the maximum inflation pressure of the tyre to cover all loads being applied and not specific loads which often, are not near the plated weight you actually travel at. The volume and pressure of the inflation medium is what carries the load and if it is not sufficient then the tyre can suffer damage, hence why it is extremely important for the correct loads to be obtained, in order to inflate the tyre correctly. Experience shows that due to the weight distribution of vehicles in the leisure industry such as motor homes the likelihood of overloading or uneven weight distribution tends to put a greater load on the rear axle rather than on the front axles, where the weight tends to remain more consistent. It is true that when braking occurs the weight transference is to the front, but this only tends to be for short periods, whereas overloading on the rear axle can be present over long periods, when the tyres are rotating at high speed.