Hi
We have one and phoned the Daf dealers recently, he said depends how many travelling we said two horses so he said 90, but worth you phoning your local dealer to check
90 Psi min 100 max better to have them at the max presure
low presures cause heat build up and can cause a blowout ..
If you arnt sure about the condition of your tyres... im sure a tyre place would be happy to advise you...
hope this helps