Quite frankly I don't give a rip about how much pressure you guys would like to run because it won't affect my life one little bit. If you want to wear the centers out in only half of the tire's life span go ahead. In the meantime I'll continue running my 24/20 psi and enjoying my nice soft ride as well as the very best traction.

 

Seriously? The "MAXIMUM LOAD" above the weight of the car is 450# and we're still having this discussion?

I have no words. This has got to be some kind of joke. It has to be.

 

Outstanding! That means in the future you can keep your outdated, ill informed opinions on the matter to yourself. Great news for the forum!

 

Problem is most of us don't give a rip roaring shnit what you run, it's when it influences some members who are new to the hot rod scene to run 20psi in their tires and have a blow out on the freeway because the tires overheat as a result of their tire pressure being too low.

With regards to tire pressure, what you are preaching is down right dangerous and someone has to step in and stop this complete : before someone gets hurt or killed.

You are doing no one a favor posting this sh*t and hopefully you will get bored and go out for walk and clear your head ( instead of being the first poster to answer a question all the time ) or take a vacation or something instead of this constant barrage of crap.

 

I get 40,000 miles out of my tires but when run at 30+ psi you'll be damned lucky to get 15,000 miles. Why only 15,000 miles? BECAUSE THEIR CENTERS WILL WEAR OUT.

 

Oh, I see. You're thinking they're talking about the max load of the TIRE...you're dividing it out across all the tires and saying "half weight is half pressure".

Huh.

I'm very sorry, but the sill placard reflects the recommended pressure at the maximum load of the VEHICLE, not the maximum load of the TIRE.

I wear the centers on the rear tires of my Corvette, but being as I put under 2k miles a year on it, I'm figuring...you know...that it's from "something else". I have several 40+ foot long instances of "something else" in my driveway right now.

I am literally shaking my head right now. I am really confused as to why this is still a discussion point.

 

I`m sure the lawyers would love to talk to you after you wipe someone out because you had a tire failure from under inflation. Especially after being told time and time again on this forum that you are wrong. Ignorance is bliss. Just adding some fuel....lol

 

So in 1975 it only took 20 psi to hold the car up and now it takes 35 psi?

 

In a word: Yes.

It seems that the tires were built differently. Or they hadn't quite figured out "Radial Tires For the Masses 101" yet. Dunno. Things change.

My earlier post was pretty clear, I thought, in the apparent progression of this issue through the years.

 

Did you read any information about tire construction? Go look it up we will wait. Bias ply tires were being used then bias ply has stiffer sidewalls therefore require less pressure thats where the recommended pressure comes from. Unless you are running bias ply tires your air pressure recommendations should come from your tire manufacturer.. Why is this so hard for you to understand? Call the manufacturer up and tell them what you you have and see what they say.

 

Actually, Mr. Kacyc3, the interesting point of my investigation was that GM recommended 20/20 tire pressure for the first-year application of their RADIAL tire. I do not know why.

In later years (from 1974 to 1982), the recommended tire pressure increased incrementally as the tire width also ultimately increased from 225 to 255. This culminated in the 1982 recommended tire pressure of 35/35 for the widest tire they had yet fitted to the car.

This is an interesting counterpoint to Mr. TooBroke's assertion that the tire width is instrumental in his ability to run lower tire pressures.

As I said a couple of times earlier, I suspect that as Radial Tires continued their development over the 'early' years, the structural adjustments required that more and more pressure be run for the contact patch to maintain its shape. It is very difficult to find historical information on this hypothesis.

The "most modern" data point we have is that of the 1982 Corvette. And the recommended tire pressures are exceedingly similar to those found on other period, and later, cars.

I'll say it this way:

If I take my BFG tire and put it on a 1982, the door sill says I should run 35 PSI. So I start with 35 PSI. I take THAT SAME TIRE on THAT SAME RIM and put it on a 1974. The door sill NOW says I can run 20 PSI. So I deflate my tire to 20 PSI and go on my merry way.

Makes sense, right?

I'm sorry, but it does not to me.

From 1970 to 1982 to NOW, we had different gas, different brake fluid, different oil, different lots of stuff. Why is it such a stretch that tire technology also changed in a way that requires a different approach to pressure?

 

HUH? The car is rated to carry 450lbs of driver and cargo. In what dreamland does hauling say 150lbs instead of 450lbs (300lbs under the maximum load rating of the car) mean you change tire pressure from 35lbs to 20lbs?

 

I'll continue to use sidewall skuff to find my ideal air pressure.

As for Dragsters "at least in the NHRA" the PSI is set to get the tire to the correct diameter.
It's checked before each run as the ambient temps change.

 

oh please lets not get into a fuel cars air pressure.
something to do with launch contact patch, tire growth at a given rpm at the top end. I just wouldn't be able to live with his explanation that they run 7.0 psi LOL

sorry don't care if you are an engineer I know a lot of smart ones but are stupid with no common sense....where do you fall?

so I am looking at running 18x9 and 1910 inch wheels on my. So with that said the tires will be considerably wider are you saying that I can use less than 20 psi.per tire? because that's the way it sounds by going with a wider tire.

 

If the center of the tire wears out first the pressure is too high. If the outer edges wear out first the pressure is too low. Thru 27 years of experimentation with the 255X60R15's I have found 20 psi will give perfectly even tread wear and the longest tire life with a 350" engine.

A 255X60R-15 is rated for a maximum load of 1875 pounds @ 35 psi. Reduce the load by 1/2 and the pressure can be reduced by 1/2 to maintain the same tire profile. Its real simple guys.

 

So why did G.M. decided on the 35 psi pressure? Over the years the big three automobile manufacturers found owners would sue them over anything. Knowing the average owner would NEVER check their tire pressures they decided to inflate them to just short of bursting to avoid product liability lawsuits.

When was the last time YOU checked your tire pressures? 3 months ago? 6 months ago? A year ago? C'mon guys, be honest about this. I usually check mine about once a month but there are times several months will pass by between checks and I'm not proud about that.

 

Did you guys read the "Tire Bulging At Low Pressures" thread that I started several months ago? I spent about an hour of my time one day carefully measuring the width of my right/rear tire at pressures from 35 psi to 0 psi in 1/2 psi increments to find out the effects of dropping pressure. My testing revealed my tire only bulged a TOTAL of 3/16" @ 20 psi or .093" per side; way too small to detect with the naked eye. I continued dropping the pressure 5 psi at a time and it wasn't until it had dropped below 5 psi when the bulging became readily apparent.

The point I'm trying to make is you can't tell if your tires are low or not by just looking at them. As long as a minimum of 20 psi is kept in a 225 to 255X60R15 tire you'll never have any problems in average driving conditions.

 

The entertainment value of this thread(and a few others) is quite high.

 

First, I completely disagree with the linear relationship between rated tire capacity and weight bore by said tire. There is zero merit in the argument that "because a tire rated at 2,000# only carries 500#, so I can run 1/4 the pressure required for it to carry 2,000#". Zero merit.

The key factor that needs to be measured/discussed instead of sidewall bulge is the relative pressures being imparted ACROSS the contact patch of the tire. The Tire Rack article that was shared previously does the best job of demonstrating this issue.

The air pressure inside the tire not only 'supports the weight of the vehicle', but also the shape of the tire. Driving on asphalt is one situation, but things change greatly when you drive through rain or a puddle. The water is able to push with variable pressure on the tire. If the pressure is not high enough to properly support the center of the contact patch, it is able to "cave", creating a collection of water at the very center of the tire...EXACTLY where you DON'T want it.

Again, the 4th image in the Tire Rack tests demonstrate this phenomenon perfectly.

I'd like to offer the visual of the tire being a boat and the air being the ribbing. Without the ribbing, or battens, or SOME type of structural support, the bottom of the boat would give way to the pressure of the water across its span. It is the AIR PRESSURE in the tire that PUSHES the center of the tire into contact with the ground. Without air, it would be structurally unsupported. The steel wire inside the carcass of the tire holds the tire together and resists pressure from WITHIN. It does nothing to support the tire from external forces.

Simple "I'll measure the sidewall bulge" testing DOES NOT capture the relative weight at the center of the contact patch. And this part of the tire is BY FAR the most critical point in the overall profile of the tire.

All that said, I do not doubt that there is generally even wear across the face of the tire in normal conditions. Additionally, I am 99.998% certain that if said tires were run at 28 PSI instead of 20 PSI, there would be little measurable difference in the amount of wear across the face of the tire. I concede that in a laboratory setting, one probably could find a measurable difference (it would make sense, after all), but I'd be as-surprised-as-a-human-could-be if said difference would alter the overall mileage gotten from a particular tire.

In summary, the air pressure in the tire does two things:
1) Supports the structure of the tire in ABNORMAL conditions and
2) Generally reduces the heat generated by flexing and friction
And heat, as you know, is the enemy of many things mechanical.

If I could, I would do the "Formula 1" thing and have THREE heat sensors...one at each shoulder and one in the center. I would then adjust the tires of ALL of my cars so that in normal driving conditions, the heat sensor in the CENTER of the tire was JUST ABOVE the heat generated at the edges of the tire. I would then know that the tire was properly inflated to provide suitable support to the center of the tire structure.

Without the "Formula 1" thing, I'm left to use logic and reason to inflate my tires. And that's what I fill my tires with. Logic and reason. All the way to 30 PSI. More if I have shoulder wear.

MOST of us seem to be on the same page. This will be my final post trying to convince the outliers of the merits in properly pressurized tires. There really aren't many other facts I can offer on the subject.

Thanks to all,

Keith

 

Great post Keith.