Some hubs are stamped inside with a maximum PSI based on the mythical "average" rider and "average" tire. "Maximum" and "best" are very, very different concepts.

In the 1980's, most 700 x 25mm tires were stamped with a maximum PSI of around 100 PSI. And, as it turns out, that is the PSI level that yields the best combination of comfort and performance for a typical rider weighing 150 pounds to 170 pounds.

Today, primarily for marketing reasons, not performance reasons, some 25mm tires are stamped with a maximum PSI of 140 PSI or 160 PSI. That is a safety rating that has absolutely nothing to do with the PSI that provides optimum performance. With a 25mm width tire, and a 150 pound rider, the "best" PSI is around 100 PSI, just as it has always been.

I've never been able to decide WHICH sort marketing hype shows the most disrespect for the IQ of cyclists: tire companies marking tires at silly PSI levels, or Shimano adding an extra cog to its cassettes every couple of years. If we live long enough, the morons of marketing will have us on tires marked 300 PSI, riding bikes with 20 cogs.