The tires fitted, at the max pressure have the load capacity for that vehicle. eg max load 1150 @ 69PSI gives a load of 2300Kg per axle which is greater than the GAWR for the back and the front axles. So they are OK for that reason. Pump them up to the 69PSI at the back and see what difference it makes.
Have you driven a vehicle like this before ? Driving a motorhome is not like driving a car. They are top heavy and have a lot of flat side area, so do sway and move around because of the side area and the wind. A heavy truck base is more stable but the smaller truck chassies do an OK job if you drive it sensibly and drive to the conditions and take it easy.
Possibly get a mechanic to check there are no worn, loose suspension parts or wheel alignment adjustments to be attended to. Fitting extra heavy duty springs may help if it loaded to the max weight.
We have a 5t motorhome and run the same size tyre as you (but duel wheels). We put 65 in front and 60 at rear. However we have done 1.5 laps of Aus etc over 6 yrs and there are not too many gas stations with tyre inflators which go over 60psi. Therefore we run 60 allround.
Yes you got that right ! About service centre pressures . Out there WA . Fittted air hose and pressure went from 80 down to 60 !! Ours run 90-100 Lb . So out with the 12v portable compressor !!! Sheesh !
Nev Bartros I have the same van and had a similar problem. The van wandered all over the road .I was told it was the steering rack that there was a recall years ago on them .I had that replace still no better.Had wheel alignment didn't make any difference.
Noticed on my tyres that the maximum pressure was 55 psi and the placard had said I could run 80 PSI. I checked with the tyre manufacturer and they told me I had the wrong tyres fitted to the van.I had them replaced and now it tracks in a straight line a pleasure to drive. By the way the tyre place who originally fitted the tyres replaced them quickly for nothing .I now run 70 in the rear and 65 in the front
