oct1949 is right, the pressure rating on the side of a tire is generally the max safe pressure allowed by the tire maker.
If you think about it, it makes sense.
No tire maker can predict in advance what year, make or model of bike the tire is going on when they make it.
So there is no way a tire manufacturer could know in advance what the tire pressure should be.

 

Each to his own. For over 30 years I've been using the max pressure rating of a tire as a general guideline of how much pressure to put in it. I generally run a couple of pounds under the max rating. I never run less than 90%-95% of max rated pressure and I would never run more than the max rated pressure. It's always worked well for me (never had any handling or uneven wear issues) and I've never had to ask anyone how much air to put in my tires.

 

Tire pressures stated in the manual are for the tires that came on the bike. Optimum pressure is not necessarily going to be the same with different tires. Different tires also have different max pressure ratings.

 

None of the links would work for me. Am I doing something wrong?