Thanks everyone,
Based on the info about wheel width and the increase in sidewall width, I guess I won't be getting any wider wheels!
I have tried air pressures from about 15 and on up to 25 p.s.i.
Its fine when just going straight! As soon as I take a right hand turn though...I can hear the squeak start.

I may as well, look into some other tire.
AND probably some suspension/chassis improvements