Beware of 'approved' dealership standards.

You don't say what vehicle it is but 72 & 78 psi sound very high, the ride will be quite firm unless it is a very large vehicle, you may yet end up being tempted to reduce them to nearer what they were......

Was the tyre pressure in a "handbook" from the motor caravan maker or the base vehicle maker? on the door piller,as that is the Max tyre pressure not that the conversion can run at,as most conversions can run at lower pressures,which then will also stop your teeth being knocked out 

our last motor caravan had a tyre pressure of 55 psi front & 58 psi rear and that was stated in the conversion handbook

Thanks for both of these comments. These are the pressures stated for the conversion (motorhome). However I will dig a deeper and possibly contact the tyre manufacturer for additional information.

I would be tempted to ring the Workshop Manager at Marquis first and ask for an explanation, there may be a good reason.  (Which of course you should have been told).  If you google your particular make & model of M/H plus the word tyre pressures you might find stuff written previously....

I know if I type mine "Autotrail blah blah tyre pressures" loads comes back and the expressed wisdom seems to be you need to weigh the van per axle & then use a pressure chart from the tyre manufacturer etc.

It may be that marquis have been through this excercise already......(but they should have explained that).

It sounds par for the course for Marquis to me. 

As mentioned above and widely elsewhere the only way to establish the correct tyre pressure for your particular vehicle is to load your vehicle (including passengers) water fuel etc as it would be loaded for touring then  take it to a weigh bridge and obtain accurate axle weights for each axle. Curiously that exercise for my vehicle showed an almost equal load on front and rear despite perceived wisdom being that the rear should have a higher pressure. Then calculate tyre pressures for your specific tyre size and specification based on these loadings. Your tyre manufacturer may assist for example Bridgestone gave me pressures within an hour of an e-mail request but Michelin apparently just quote maximum pressures. Getting the pressures right makes a considerable difference to comfort handling and safety and over inflation can contribute to valve failure. Any pronouncements not based on axle loading are only general guidance. There are pressure tables available on the Tyresafe website but make sure you match loadings to correct tyre size and type. 

The pressures of 72.5 and 78.5 will probably mean you need to buy stronger adhesive for any false teeth you may have.

Those quoted are, in the real world, bone shaking pressures.

I run mine front tyres 51psi (3.5 bar) and rear tyres at 61psi (4.2bar) after consulting the Continental Tyres pressure guide and weighing both front and rear axles.

You need to go to a weighbridge, probably about £5, and weigh the vehicle in full holiday mode.

Once you know that you can ascertain the correct pressures.

The pressures the dealer sent you away with are not potentially dangerous and, depending on the axle weights, may even be the perfect setting.

If you have Michelin Agilis Campers on the rear, then Michelin will always quote 80psi for the rear. It was, apparently, agreed by all tyre manufacturers because motorhomers always overload the rear axles. Only Michelin seem to stick with this figure.

If you go to a weighbridge, check the tolerance factor and when it was last calibrated. The one I use is calibrated every 6 months but can be 5% out; the ones used by the DVSA are within 0.5%. It also costs £10.

Your manual should be the starting point for tyre pressures, then you should check the make and rating of tyre to see if they match anything quoted in the handbook [they don't always] and then either wander off down to the weighbridge, get the van and each axle weighed in full touring mode, and then ask the tyre manufacturer or go to a website such as Tyresafe.

Or you could just cut through everything and ask Marquis what they were doing as Tintent says.

Most motorhomers run their tyre pressures below the manufacturers recommended figures because those are for maximum load and the lower the pressure, the better the ride [within sensible parameters!]. 

Since my first post of this topic I have received further responses from both Marquis and Michelin. Marquis suggested 72 front and 75 rear and Michelin have quoted 65 land 80 rear. Obviously there will be a range of pressures which is acceptable but what is this range? If for example the maximum rear pressure is 80psi then how much can this be reduced and still remain safe. My basic understanding is that if a pressure is set too low or too high then either can cause excessive wear and ultimately tyre failure. Obviously I want the ride to be comfortable but I want it to remain safe. I genuinely thank those members who have provided advice and guidance on this matter but I feel that advice and guidance should be provided by the manufacturers at the point of sale. Anyway, I'm getting off my soap box and driving to the local weighbridge and then hope I don't miscalculate the pressures!  

Marquis aren't the only so called approved that have failed dismally.  I have had my caravan back from a so called approved case with a serious gas leak because they didn't attached the gas pigtail correctly - it was less than finger tight at the bulkhead end!  So it seems best not to be entirely trusting even though they have all the right credentials.