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Old 05-02-2013, 11:05 PM   #21
Elizabeth
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Quote:
Originally Posted by 2012silversel View Post
Exactly, psi increases 1 lb for every 10 degree rise in temp. Lets say you set your pressure today at 41 psi and the temp is 70, you drive and the tire heats up 30 degrees and now your at 43, in a week the temp is 90, the road is hotter and you tire heats up 40 degrees, now add 6 more psi and your rolling psi is at 47. Like what's already been said, the trade off for 1-2 mpg's isn't worth early tire replacement or a possible blow out. People with big brains and smart calculators have designed and determined the tire should be inflated to 35psi for safe, efficient and long life, I stick with the recommended pressure on the door sticker.
wrong.
The tire sidewall is cold pressure. So 51 PSI when "cold". So 51psi is safe when cold ,and the increase from driving is also OK. The sidewall rating takes into account the added heat/PSI increase from driving. (do you really think with lawsuit crazy lawyers, that the tire manufacturer would not take into account heat increase? the rating on the tire takes that into account

Now where I live the temps fall to well below freezing in Winter. So I actually check them at freezing in late Fall. Then in Spring I check them when it is about 70F outside. So I am good all Summer. (Even 100F no problem..)

I am happy the quoted person wants to be safe. not a problem. The issue is trying to tell others misinformation to attempt to stop them from doing this simple step to increase handling.

And "early replacement" where is that from? what sort of nonsense is that?

I have been running much higher PSI for 15 years.. And NEVER had a tire lose tread from center to cause early replacement.. In fact the tires wear far more evenly with higher PSI.

The one point I would make is if you wish to keep the tires wear even if you do not rotate,( I do not) is to have between 5 to 8 psi LESS in the rear than in front.
For a V-6 use 8psi, for a 4 banger, 5 psi higher in front.
As i mentioned.. I run 40 rear, 45 front on my Focus
(On my Contour SVT, I used to run 37 rear, 45 front, where 32 was standard)

I actualy did the tire print test on my SVT Contour. Where i checked the contact patch front and back.. finding the perfect patch with the 8psi difference..
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Old 05-02-2013, 11:16 PM   #22
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Here is a link to an article by someone who may have some knowledge of tires and psi's. Some good info, backing up and debunking some of what has been said here.

http://www.popularmechanics.com/cars...unked-10031440
Thanks. Agree an excellent article.

((and I agree with the comment about the Ford Crown Victoria psi.. A V-8 yeah, 10 psi difference..))
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Old 05-02-2013, 11:35 PM   #23
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I just found the article on a google search. But it is concise and backs my thoughts that as long as your are between 35(door jam recommendation) and 51(or max psi cold) you will be fine. There is no real danger of catastrophic tire failure due to over-inflation until near 100psi, not 51, not 55 or even 60psi. Manufactures build in a large "safety margin" for the "Jay Walking All-stars" out there and those with faulty tire gauges. So go ahead and experiment with your pressures until you find a setting that suites your driving style and needs. If you don't have a clue, Elizabeth has some good numbers similar to what I run, or start with 38-40 front and 35 rear or 38-40 all the way around. Or just do 35 all the way around and keep a check on those pressures, because like the article says, it is better to be 3-5 over the 35 than 1 under the 35, thus backing my point that the 35 should be used as a do not go below number not necessarily the be all end all number.
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Old 05-03-2013, 07:30 AM   #24
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I like threads like this. Lots of well thought responses that make sense.
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Old 05-03-2013, 08:07 AM   #25
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Obviously, I'm completely wrong. In order for me to understand thermodynamics and heat expansion, I need help from the experts. If I have been driving on the freeway for several hours and I stop for fuel, I should check my tires and if the pressure is above the recommended setting on the door panel, or the pressure I chose to inflate them to, I should release air from the tires to match the desired pressure, correct? Elizabeth, if I understand correctly, I can have my tires inflated to a cold psi of 51 and under all driving conditions it will be safe and won't cause any premature or excessive wear on the tire?
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Old 05-03-2013, 09:25 AM   #26
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If you are driving normally (not RACECAR) and your car is not overloaded (rear tires supporting a loaded trailer or something), your tires will be fine with the increase in temp. As stated above, the lawyers have taken into account the tires load rating and normal temperature increase in relation to it's max pressure listed on the sidewall.

Better yet-nitrogen
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Old 05-03-2013, 10:47 AM   #27
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Quote:
Originally Posted by AZfocus2012 View Post
I usually run 5%-10% under the max on the sidewall of the tire. I ran my OEM's at 45-48psi and they still had more tread in the middle than on the sides when they were gone. Ride is a little firmer, but mpg's are better and cornering is better.
Agreed I do the same
And never have/had problems
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Well we only have 2 seasons here. Winter and road construction.
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Old 05-03-2013, 11:30 AM   #28
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Quote:
Originally Posted by 2012silversel View Post
Obviously, I'm completely wrong. In order for me to understand thermodynamics and heat expansion, I need help from the experts. If I have been driving on the freeway for several hours and I stop for fuel, I should check my tires and if the pressure is above the recommended setting on the door panel, or the pressure I chose to inflate them to, I should release air from the tires to match the desired pressure, correct? Elizabeth, if I understand correctly, I can have my tires inflated to a cold psi of 51 and under all driving conditions it will be safe and won't cause any premature or excessive wear on the tire?
Nice discussion!

Had to "Jump In" to respond to this one.

The one thing you DON'T want to do, is reduce tire pressure to "normal cold" readings when it has INCREASED due to heat from driving. This causes under inflation, as you'll note once they cool down and are under the recommended value.

Also, the "cold" 51 would be "safe" if that's the max printed on the tire, but it would be quite uncomfortable. Leaves no room for front to rear difference to improve handling while remaining within the recommended zone as well.

Other notes:

Max. inflation pressure was once explained to me by a Dunlop rep. as the pressure used to inflate the tire during the molding process. This corresponds to the max. load capacity pressure, and the "shape" of the tire should be normal at this value.

Increased pressure (by approx 5 psi. over "sticker" recommendation) is often suggested in owner's manuals for "extended high speed driving". This reduces increase in pressure from heat buildup, and improves handling.

"Sticker" pressure is a compromise, as prev. noted, and is related to the actual maximum recommended load (vehicle & passengers, etc.). You'll see a note as to vehicle load capacity (cargo, passengers) on that sticker.

Pressure differential, front to rear, is used to adjust handling. Higher pressures give greater cornering traction, and with the vast majority of cars being "tuned" for understeer from the factory using a bit more in the front evens things out a bit.

As to those Explorers, I've seen MANY tooling down the Hwy at 80 or more, with what looks to be about 15 psi in the rear.... Need I say more?

Cheers!
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Old 05-03-2013, 07:05 PM   #29
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Very glad I opened this topic up, tons of good information. I've decided to try 42psi front and 38 rear based on everything I've read. With the possibility of increasing that for longer trips? The car is driven daily so no racecar stuff. The tires are 215/60/16 conti's so that's probably aiding the comfort tolerance level with the psi increase.
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Old 05-03-2013, 09:53 PM   #30
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for every 10 degrees of temperature change your tires will change by 1 psi. so youll be safe if you go from fargo to death valley.

tires are rated for max load at max rated speed at max pressure. the worst conditions possible. there is a built in buffer zone to cover everyone's butts. your happy the companies are happy and the lawyers are happy.

i did have a f150 with a hung up caliper come in off the expressway. my dad said it was pulling and had a funny smell. 3 tires tested at 38 psi and the front left was 98 psi. max value on that tire was 50psi. i pulled the valve and stepped back. that air was wicked hot and you couldnt touch the wheel without receiving a burn
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