So I have an older Roubaix road bike that has 700 x 25 tires. I used that calculator thing and is says to put 90 psi in the back and 88 psi in the front. Normally I went 120 in the front and back. Basically the max. Going 90 now feels different. You feel the road more. More rumbling if that sounds right. Is that correct? Just did a small back and forth in the driveway. I like it because it absorbs everything where as before it was like hard hitting every pebble or road crack. Again is that normal this feeling with the new pressure and is 90 a good average? Thanks

the max pressure on the side of the tire is just that - the max pressure the tire is designed to safety take, not the appropriate working pressure, which takes into account rider+bike weight, road conditions, riding style etc. Pressure calculators are a good starting point, but you should adjust this based on your individual circumstance. I tried a calculator-based measurement, but started getting the occasional pinch flat, which I never used to get when I simply « blew them up hard ». This even though I watch where I’m going and unweight when going over rough surface or gravel. I upped the pressure by 5 psi over the calculator recommendation and pinch flats have stopped happening

As long as you are happy with it and don't get pinch flats, then whatever pressure makes you feel good about your ride. Or you can do whatever everyone else tells you your tire pressure should be.

You didn’t tell us your weight but probably 85-90 is right.

Common mistake is to think the “max” pressure is the best. It almost never is, but that said I expect a majority of cyclists don’t know that. Sigh.

my weight is 205 lbs. I think the Specialized Roubaix is 20 lbs. My gear? Who knows

I would say 90 is a good start. Tweak up/down a few psi to see how you like it.