is 30 psi ok for 18's?

the shorter the side wall generally the more bumps and things you are going to feel going down the road....the ones that you didnt feel when you had your old 45 or 50 sidewall.

air pressure does effect the way the tire wears, over inflated it will wear alot more in the middle of th tread, under inflated, its going to wear alot more on the outsides of the tread.

50 seems like a bit much, i think i run about 32...

here is the real scoop on a scientific way to set your tire pressure, and if those chumps on corner carvers say diff well f&$k'm. get a digital laser pointed temp gauge, go drive the pee out of your car for about 10 minutes then stop and measure the temp across the tire in 3 spots. if the temp is higher in the middle it is too high and if the temp is higher on the sides it is too low. do this until the temp is even across and this is your optimal psi. btw using this method the front pressure will most likely be diff than the rear, something to keep in mind when rotating if applicable. the temp gauge will run about $75 but has many more uses such as finding a miss, checking your cats etc...

I run 30 PSI in my fronts and 25 PSI on the rears. 16-18 PSI at the track

tire should say min and max psi on it. Personally on an 18 id run 32- 36 psi depending on how they start to wear