Time to replace tires?

Get something quiet this time. The Hankook Optimo H727 is one of the few quiet tires and it does make my xB perfect. The Scion xB is the most ideal car I could find several years ago: roomy like a bus, 32 MPG downtown and priced firmly under $15K out door. The only imperfection is noise: significantly noisier than Corolla - more like Civic.

The H727 is rated on top by Consumer Reports and users (Tire Rack) on pretty much everything, including snow traction, with a whopping 100K mile tread warranty at very reasonable price ($72). In addition to low noise, this tire is also very comfortable, providing much softer rides than the Goodyear Eagle LS that came with the xB.

Rebates are almost always available for tires, for example, Hankook is currently offering $50 and Discount Tires $100. Rebates are often found in CostCo coupon books, but they are actually offered by manufacturers. You can always find better deals online even with shipping added (about $50) and far more choices than any local stores.

Walmart is the cheapest place to go for tire installation, $46 out of door for a set of 4, even lower than CostCo ($60). Adding up all the cost for shipping and installation, my final bank damage is $330, same as CostCo's quote for the crappy Bridgestone Insignia SE200 and $100-$300 less than other local stores for the same tires.

Now what's the pressure should I inflate tires to? This is a very simple question but full of confusing answers. There are two numbers: one on the car door and the other on the tire sidewall, which one to follow? This is Hankook's suggestion:

"Generally, the optimum inflation pressure is about 90% of the maximum level."

The H727 is marked on its sidewall as max 44 PSI, so I pump it to 39 to save gas and tire life. This is much higher than 29 on the car door. I might go lower for quieter and more comfortable rides, but the lowest I'd go would be about 3 PSI above the number on the car door, i.e., 32 PSI.