So I bought back my 1979 RX-7 as noted in an earlier thread. It is now a beast. And it has 185/60/15 tires on it now! I know you can't go by what the tires say, and now I can't go by what my car says (originals were tiny 13s). So how much air should I have in my tires on a hot summer day in Texas?

 

as long as they're mounted on rims within the specified width range, why not? i mean you may not want to inflate them to the exact limit in the height of summer, but i would imagine the manufacturers probably have already taken heat expansion when they put that MAX INFLATE or DO NOT EXCEED pressure on it.

 

Wear pattern is going to determine your best pressures on a street car. Set your pressure for a reasonable PSI and monitor the wear with a depth gauge. That being said, I live in AZ with temps basically the hottest in the US and running 35 PSI on my car has given me no problems. You want to keep checking and adjusting the pressure at least monthly as natural loss will add up.

 

with a Mazda, its usually pretty easy. there is or was a tire pressure label in the door jamb.

in a street car, inflate to this pressure when its cold.

in a race car start with this pressure hot. race car may end up in a different place after testing, but Mazda's spec is a good start.

 

185-60-15 is an incredibly odd tire size... Too tall a sidewall.