Tires: Proper Tire Inflation for Car - NOT OEM Tires, proper tire inflation, pirelli p zero

Question
QUESTION: Hello!  I have a 1994 BMW 325IC...have had it for almost 13 years!   And a few months back I got new (not OEM) tires on the car with new alloy rims.     The new size I have on the car now is 225/50/R16 the tire brand is Pirelli P zero nero...etc.   I am really confused what my tire pressure should be on these tires.   The manual for my car says something like 29 psi in the front and 32 psi in the back....but this is for the smaller OEM tires....and I'm not sure at all what the correct PSI should be for these new Pirelli's.   Can you help me?  Any guidance is much appreciated!  Harrison

ANSWER: Harrison,

Yes, I can help you, but I need to know what tire size you put on.

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QUESTION: Hello...thanks....here are the detailed size tires

OLD tires were size:  Michilen 225/55VR 15 with a recommended psi front 29 and back 32.

NEW tire size is:  Pirelli 225/50R 16 92W

Any help you can provide for the proper PSI for these new 225/50R 16 tires is great appreciated!

Thank you,
Harrison

ANSWER: Harrison,

Opps, my mistake.  I thought you had given me the old tire size and i now realize you gave me the new tire size.  I still needed both of those, though!
You need to use 2 psi more than what the vehicle placard says - 31 front / 34 rear.

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QUESTION: Barry-

THANK YOU!  very much for your help and the new psi numbers.    

How do you figure that out..is it a complicated formula?

You will not believe that when I checked the current psi in all four tires today they are all at just 20 psi...so WOW they are really way too low...and I assume that is dangerous and bad for the tire too.  

Thank you very much again...I will put air in these tires tomorrow am!

...and if you have a chance....reply back with the calc to figure the new psi...I want to learn!

Harrison

Answer
Harrison,

It is a complicated formula, so it is published in the form of tables.  Unfortunately the tables are not allowed to be published on the web, because the folks that generate the tables publish these in the form of a book and - well, let's say that this is their only source of income - and as a result the books are pretty pricy.  The books come out yearly and the current book is priced at $60.