The great thing about Morgans is the ability to change things to suit you , your style of driving and the road conditions you are driving on.
I would not worry going as low as 18 psi as a low start point and increasing from there. in 2 psi increments.
I run mine at 24 all round for most of my driving , but would consider going up to 26 psi when fully laden and running fast on main routes/motorways.
Also experiment with a differential between the front and rear and see what suits you, most non Morgan folk will go for a higher pressure at the back , but in our case this is wrong and will increase the understeer, a couple more psi in the front will help combat that, but don't overdo it or you will be rewarded with chronic oversteer which can be tricky to catch on the limit.
