newby Bob
I couldn't help but make a comment on the discussion, for those interested in some graphic footage of a tyre under deflection in race conditions, get a hold of Bathurst 2006, V8 Supercars Australia, where a camera was mounted under the Ford of winner Craig Lowndes. Bathurst is a twisty, mountain circuit where an annual pilgrimage takes place in October for the 1,000 Km event, which is renowned as a heart breaker. My experience is limited compared to most who have commented herein, however for what it's worth, there are as many variables as types of use, eg drag racing, street and circuit racing pressures all vary, especially with the width of rim and vehicle weight. Loaded radius is a starting point, low profile tyres require much higher operating pressures than is the norm, 38-42 psi is not unusual on a street driver. A particular tyre size will require different pressures under different conditions, wheel width, vehicle weight/load, operating conditions and in the case of the above mentioned race clip, driving conditions, operating temps, etc. Regards, Bob