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Old 05-07-2008, 10:06 PM   #1
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How much tire air pressure is still safe?

Anyone know how high you can increase air pressure for your tires before you hear this really loud noise. I am assuming that the suggested pressure range has a built in safety factor but don't know what it is. Also, is there a study somewhere that will show increase mpg by increasing air pressure in increments...
Thanks
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Old 05-07-2008, 10:33 PM   #2
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Originally Posted by molinee View Post
Anyone know how high you can increase air pressure for your tires before you hear this really loud noise. I am assuming that the suggested pressure range has a built in safety factor but don't know what it is. Also, is there a study somewhere that will show increase mpg by increasing air pressure in increments...
Thanks
I visited the local tire store and they were very adamant that over inflating the tires is a bad idea. I heard on Car Talk that up to 200psi the tire won't burst. But the guy at the tire story was telling me at 60psi I was very lucky that I hadn't had an accident yet and that I had a very short fuse so to speak....
they also said "the max psi" on the sidewall is not the max recommended tire pressure, but referring to something else and that most tires should be inflated between 25-34psi with 34 really being the upper limit. I agree 60psi is too high, but not going higher than 34? sheesh. At 60psi the handling makes me a little nervous, but for the way I drive... I really don't see it as much of a problem. I suppose running firmer tires would make them more susceptible to lacerations from nails and glass and what have you. It also makes your stopping distances longer, (But I don't know how significant of a difference it makes)

That's the extent of my knowledge and experience. I'd be curious to hear what other people think--although there are like 45 topics on this now. (do a search of the forums)
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Old 05-07-2008, 11:22 PM   #3
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Most of the owners manuals that I have read (I read them while ridding in other peoples cars all the time) recommend bumping up the pressure by 4-6psi if you do mostly highway driving, so that would make a 32psi tire 36-38psi, and this is mostly because the tire flex creates heat and shortens the tire life by softening the side wall to the point that it can blow out, tires that flex less last longer.
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Old 05-08-2008, 03:39 AM   #4
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max PSI on my sumitomos is 51. so, i go 51 on the rear and 55 on the front.

and i pass the dirt/dust test...the tires show dust on the entire tread surface.
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Old 05-08-2008, 03:53 AM   #5
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By the way, did anyone know, that tires are certified for their maximum rated load, ONLY at the max sidewall pressure!

So if you replace some 35 PSI max tires on a Jimmy or something, where GM says tire pressures should be 28, with 44 PSI tires, of the same load rating, and inflate them to 28, per GM, then you've probably only got 1/2 the safe load carrying capacity of the previous tires. Also it will probably say in the manual somewhere that tires should be pumped up more for load carrying, but barely ever really tells you the full details.
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Old 05-08-2008, 04:55 AM   #6
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When I drove my Scion XB home from the dealer the tires were inflated to 65 PSI! The max sidewall pressure was 45. They screwed up and inflated them to the pressure for the super low profile tires Toyota offered as an option. The car rode terrible and the long term results would have been serious, in my opinion (a rattletrap).

20lbs of overinflation equals a force of 20X144 pounds per square foot of pressure all over the inside surface of the tire. Thats 2880 pounds of pressure on top of the 6480 pounds per square foot for a total of 9360 pounds per square foot on the inner surface of the tire. Considering the total inner surface area of the tire is about 5 square feet, you are now talking 46,800 pounds of force on the inside of the tire!

23.4 tons of force constantly working to create a catastrpohic blowout.

I was once following a concrete truck, that carries that kind of pressure(65-80) in its tires, the left front tire on the truck (one of those super wide ones) had a bulge on the sidewall about half the size of a basketball, and the truck was full. I got past it very quickly but the Renault R8 that was right beside him did not. The explosion blew the R8 into the grass median and it spun around about 4 times before coming to a stop. The driver literally crawled out of the car.

Just my opinion folks but it seems my VX works fine with 36 PSI all around, without seriously compromising the ride quality, or causing uneven wear. The tires are almost 15 years old, whch is a major factor, and rolling resistance seems to be very low, as it will start to coast down almost the slightest grade.

In experimentation you like to go to much then too little, to determine what is the just right range in adjustments.

Personally I dont know how much better my mileage would be if I added 10 PSI to the tires, but in my circumstances (and only mine) I don't think the risk justifies the reward.

regards
gary
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Old 05-08-2008, 06:59 AM   #7
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Quote:
Originally Posted by R.I.D.E. View Post


Just my opinion folks but it seems my VX works fine with 36 PSI all around, without seriously compromising the ride quality, or causing uneven wear. The tires are almost 15 years old, whch is a major factor, and rolling resistance seems to be very low, as it will start to coast down almost the slightest grade.

regards
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Honestly, I would be more afraid of 15 year old tires then 10lbs over inflation.

YMMV
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Old 05-08-2008, 10:10 AM   #8
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Originally Posted by BBsGarage View Post
Honestly, I would be more afraid of 15 year old tires then 10lbs over inflation.

YMMV
agreed. the concrete truck didn't have trouble because of the inflation but because of a flaw or damage to the tire. if the tire isn't old and dry-rotted, bald, or damaged it will hold over 100 psi just fine.

legally, you won't pass most safety inspections with tires over 5 years old. the rubber does have a limited lifespan, if you doubt it, take a brand new rubber band compared to a 10 year old rubber band.

My Cressidas tires are rated 51psi, I keep them at least there. The trucks rated for 35, I keep them at 40 even tho the rears are old and bald. They took it just fine carrying 800lbs of camaro on the highway for 5 hours
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Old 05-09-2008, 07:02 AM   #9
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tires have a max psi on them from the manufacturer. IMO, there's no point to exceed this manufacturer recommended max.

my kumho's max is listed at 51. i just pumped them up to 45psi wednesday night.

always go by the rating on the tire, never the vehicle owners manual
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Old 05-09-2008, 08:01 AM   #10
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I've been at or a little over the max recommended psi on my 13s for my VX for at least 15k miles now with no ill effects.

In the owner's manual it does state to pump up the tires more for extended highway travel or if you plan on driving over the speed limit. I don't do either of those things, but my car averages around the EPA mixed driving EPA whereas I drive no highway, so something is working.

My tires have a very low rated max psi, something around 35, so once these do all wear-out I'll be looking to upgrade to a tire that can handle some more pressure and roll a bit better.
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