All right lets look at the tire pressure issue with a little bit of science
Tire pressure is dependant on
2 things not just one. First you have the wieght of the car and second you have the contact area of the tire.
Pressure is defined as a load over a given area (P = F/A). So if 2 cars that have the same tires but weigh 2 different amounts, those 2 cars should have different tire pressures. Like wise 2 cars with the same weight (say 2 95 GT's
), but one has fat tires one has skinny tires, the tire pressures will have to be different. To preserve P = F/A.
If you have a stock sized tire I would follow the manufacturer's pressure recommendations. BUT you have to also check with your tire manufacturer to make sure that your tire operates in that pressure range.
If I took the 245's off my back rims and put on 275's the tire pressure would have to drop. The force ( = P X A) would be the same (the weight does not change), but the area increases so the pressure has to decreace. Make sense? Beening a engineer means that you normally can't communicate your thoughts all that clearly
.
Having said that, some tires are designed to different specifications and operate to different design applications and therefore this analysis may not be correct.