zpiloto -

Nope, that's the brain-addled pseudo-math. I meant to say 44 PSI but I was already thinking about 40 PSI.

Stupid Wetware :mad: !!!!

CarloSW2

Cool! Then my 44 PSI rated tires can go to 48.4 PSI!

(sarcasm) but my analog tire gauge only has hash marks for whole units.
My digital gauge isn't much better... it's got resolution to .5 PSI.
Guess I'll set the tires for a hair over 48 PSI to be within the 10% rule.

BTW... ever check your tires to find one tire, or both tires on one side are higher than the others? I drove north yesterday afternoon. It was sunny 70+. My left front was at 50 PSI. The other three were 47 PSI. So the side facing the sun, plus that front tire getting more brake bias than the rears heated up more than the right sides.

"I'm coming in... Gimme a 1/2 turn up of wedge and drop the right front tire a quarter pound! I'm winning this race g'damnit!"

https://www.gassavers.org/gaslog/sig.php?id=346

davidjh72 -

I'm not sure if my typo confused you or you're still being sarcastic. The "10% rule" means that you subtract 10% from the maximum PSI rating on the tire to be safe. If you have 44 PSI, you subtract 4.4 to get 39.6 PSI (as if anyone has a tire gauge that can read that!).

However, you are probably fine at 48 PSI because I lots of people like diamondlarry are running at 50 PSI, no problemo.

I think that the PSI rating is for running the tire at it's maximum speed rating. Soooo, keep it under 120 MPH, mister!

Segway ... From a mechanical engineering standpoint, you want to be "liability safe". When a mechanical engineer sizes an AC unit, he/she calculates the building's worst possible need in terms of cooling BTUs and might add 50% to that number. In that way, the engineer is covered for when something really bad happens. The AC may never run at full capacity, but the engineer won't be sued when all the Movieland Wax Museum statues melt (because they won't).

What does all that crap I just wrote mean? There's a good chance the tire companies rated the PSI for their own legal protection.

PS - There is a really really really good tire website where I read the 10% rule, but I lost the URL :mad: .

CarloSW2

Last week I bumped the mazda's pressure up to 55. Much better rolling ability then when they wear at 40psi. They are 175 width 13" tires I would of never put that much pressure in my 195 width 15" tires I had on my previous car (SL2).

I have been running ~60 psi-give or take- in my Goodyear Assurance Comfortread's(sidewall rating is 44 psi) for nearly 10,000 miles on my '99 SL2 with no signs of uneven/abnormal wear. I'm not so sure that radial tires are affected as much as the old bias-ply tires by overinflation.

I ran 42psi in my old tattered OEM firestones(rated 35psi) for about 10k. I run 50psi in my current tires, michelin harmony's.

cfg83...

Ok... the 10% rule is: subtract 10% from the maximum. I'm going to leave mine at 45 PSI for the time being, unless the "hot temperature" after driving gets too high.

I've noticed a benefit to the increased PSI... I pull forward into my carport at night. In the morning, I don't have to reverse out of the carport. It's on an ever so slight incline. I put my car in neutral and my car rolls back slowly out. Once I'm out I start 'er up, and take off, slowly, because the end of my driveway drops off about 2 inches (almost a curb) to the road, left turn and the stop sign right there. While I'm checking for traffic, the engine is starting to warm up. I make my left turn from there and two miles from there is the freeway.

At 30/26 or 35/35 PSI, my car just sits there so I have to start the engine and reverse out. I could push off with my foot out the door, as if I've got a dead battery and trying an in-reverse bump start.

Just goes to show how higher PSI reduces rolling resistance.

Tire Pressure
 

I am running 60 PSI in 44 psi rated tires. Sure it rides rough. It really surprised me the first time I got in and it rolled back out of the garage without starting the engine. It will often do that after sitting all night. It never did that at 35 psi. I have only done this a couple thousand miles though.

I would not recommend that you go above the rated pressure, but if you did I wouldn't tell on you. ;)
Ernie