Tires: tire size, proper inflation pressure, load index

Question
I have a 1997 Infiniti I30. The tires on it are size P225/55 R16.The manuel says the tire size should be P205/65R15 92H. How can I determine what would be the safest size 16 to put on it.
Thanks  

Answer
Johnny,

According to Tire Guides, your vehicle came with P215/60R15 93H tires on 6.5" wheels inflated to 29 pdi front and rear.  This is a little bit different than what you've indicated, but there is another place to check that should clear this up.

Look for the placard on your vehicle. The placard, among many things, tells the original tire size and the proper inflation pressure for that size.  The placard usually on a doorpost or in the glove box.

Now to answer your question - The SAFEST size to put on would be that which has the most capability, which means the largest.  That way you are actually using less of its capability and therefore applying less stress.  But the limiting factor is how much room these is under the fender, which is not something that is published in a nice format.  If you can find a web site or an on line club devoted to your vehicle, maybe soeone has already done the hoework and can tell you what his experience is.

But at the very least, a tire with a 93 Load Index should be used.  A P225/55R16 has a Load Idex of 94.

Also, if you want further safety, a higher speed rating would also help (again, using less of the capability of the tire.)

Also using a slightly higher inflation pressure iproves safety.  I like to use 3 to 5 psi above the placard.

Hope this helps.