A very useful and interesting thread.
I had my original 8 inch 4 ply tyres until this week and they have lasted me more than 4 years with at least three trips to Scotland, visits to Norfolk, the Lakes and the south coast many times. They were still going strong but I was never sure of the tyre pressure; usually judging it by the deflation at the start of the trip – that said I never had any problems.
After reading the above I checked my tyres and realised that whilst still sound it might be prudent to change them prior to going away again this summer. My local tyre garage recommended the 6 ply tyres but thought the 8 inch wheel would be fine. They only inflated them to 40psi because I said I put a bit of extra weight in the boat. Otherwise they indicated 30 psi was about right.
The trailer plate gives a max tyre pressure of 45psi. I have found the higher the pressure the more the trailer bounces on the road – not something the boat will thank me for.
I try to put all heavy items in the car – only putting the lighter more bulky items in the boat.
I do however have significant problems with my trolley tyres – with punctures and blow outs (whilst sitting on the towing trailer at home) galore. I have just bought some new ones as the last blow out disfigured the rim of the trolley wheel – such is the power of the sun I guess.