I'm doing a coast to coast drive and recently replaced the stock 175/60/15 Pirellis with Yokohama S-Drives
Tire SizePart#Load IDUTQG Rating Unit Weight (lbs) Rim Width(inches) Inflated Dimensions Tread WidthTread Depth 32/inLoaded Dimensions Max Load at Cold
Inflation Pressure (lbs. @psi) SingleType
205/55R15 88W 01051 SL 300/AA/A 22.556.55.5 - 7.58.623.97.41011.08711235@51BW

The shop filled them to ~32 PSI which was recommended for the stock tires. I'm guessing these should be a bit more since they look a little low to me and have larger volume. Any suggestions on what the PSI should be? I'm looking for optimal MPG with minimal risk of wear due to improper inflation.

 

Couple of things:

Volume has no impact, 32 PSI is 32 PSI
Some newer tires just sag more. The tires on my wifes van have that look. I am constantly thinking they are low and when I check they are spot on.
If you are taking a long trip it does not hurt to put a little more air in, maybe 2 PSI.

Mostly just check them regularly to increase the life of the tire.

 

If you have stock 5.5" rims, a 205 width tire will have wider, more bulging appearance compared to the original 175, which might be make it look low.

I've been running 205/55-15 on 15x7 rims for almost 4 years with Michelin Pilot Exalto PE2 at 36 psi. Mileage is now 45K and tread wear is even across the width of the tire. They need to be replaced soon but the PE2's are now discontinued in this size and I will probably get the S Drives.

 

Thanks all. Yeah I'm on stock 5.5" rims.