OK, I’m posting here, assuming that there IS a factual answer to this question, not just opinion.
I just got off the phone with Big O Tires, after finding they inflated my wife’s Miata tires to around 40 PSI !! This also happend to me, on her car, after getting the oil changed at one of those oil change places, and it ruined the tires.
The owners manual says, and I’ve always been told that the proper inflation pressure varies by the car, due to it’s weight, mostly, and handling charateristics, and that you should ALWAYS set the tire pressure by what the tag on the inside of the door says. In the Miata, that is 26 PSI, NOT 40.
I called Big O, just to be nice, and inform them that the apparent newbie they have should be told where to find a car’s proper inflation setting, and I was told that they ALWAYS inflate tires to 40 PSI for better mileage, better tire wear , and for highway driving, and that the pressure listed in the door sill is for “city driving”.
I think he’s full of crap, and they do this so tires wear out FASTER so they can sell more tires.
40 PSI is way too high. Remember that as you drive, your tires heat up and the air expands, therefore the pressure increases. IMO, 40 PSI is a dangerous pressure level that can potentially result in a blowout, which can be a really Bad Thing at highway speeds. You shouldn’t ever exceed the maximum pressure ratings the tire manufacturer puts on their tires. Those guys are just asking to be sued.
I read The Master’s article with interest. And although he says that setting the pressure to something under the maximum limit printed on the sidewall (which seems to be what Big O is doing) the slant of the article is “can you get better mileage by increasing tire pressure?” So could that have something to do with the answer? Sure, I can see where having harder tires would reduce drag a little and give you a few percent in better mileage.
But is it SAFE?
And why then is the MANUFACTURE’S recommended pressure considerably less? Just for comfort? I wouldn’t think a Miata or a Z would owner would care much about tire comfort a few pounds of air would make.
From what I’ve read, and maybe I’ve missed something, you’re supposed to follow what is printed on the tag on the inside of the car’s door. That’s for a combination of best mileage and best performance. And I’ve read that you don’t want your perfromance tires to have too much flex in the sidewall (like when it’s underinflated) because you could, potentially, break the bead and have a spontanious deflation. Bad.
Side question is: Who benefits from having your tires wear out faster buy giving you a “not optimal” tire pressure? (Ahem, uh, if indeed someone would actually DO that, of course.) (rolls eyes)
40 psi probably isn’t really unsafe unless, as Q.E.D. mentioned, the pressure increase caused by driving brings it over the maximum psi listed on the side of the tire.
It definitely isn’t the best pressure for ride comfort, handling or tire life, however. It won’t give you the best contact area for handling, it’ll cause the center of the tire to wear faster and the ride will be harsher.
The Mazda recommend 26 psi is designed for the comfort level of the general population. Many Miata owners set it in the 28-32 psi range. Try something in that range and see how it feels and fine-tune it to your taste. Also keep an eye on how the tread wears. If the outside or inside wears faster, some adjustment may be needed. I’m using 29 psi in my '99 Miata.
Thanks Santos! Good info. I THOUGHT having the pressure that high would tend to make the tire “rounder” and wear the center more! Sure you get better mileage: the whole tire isn’t on the road!
By the way, are you runing the Pilots on your Miata?
The original tires were the Pilots. I currently have Bridgestone Potenza S-03 Pole Positions on the car. They’re great in the wet and dry, not too expensive and have a decent mileage rating.
I’ve got dedicated winter tires, so I didn’t need to try compromise and get one tire that would be mediocre all year round.
