Question about tire pressure

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  #1  
Old 05-16-05, 05:36 AM
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Question about tire pressure

I remember reading somewhere that if the tire pressure is too low, it can decrease your fuel efficiency. I guess this is because of the increased friction caused by the flexing of the tire, and the increased contact point.

My car specifies the tire pressure, but I believe this is for the default tires that come with the car.

So my questions are:

1. If I switch tire makes, should I go with the pressure specified by the car, or go with what the tire itself recommends?

2. Will I get slightly better mileage if I overinflate by 3-5 lbs, provided I'm still in the safety margin embossed on the tires?

Thanks.

-joe
 
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  #2  
Old 05-16-05, 06:05 AM
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Assuming you have the correct size tire you should abide by the recommendation on the tire placard in the door jamb, glove box or owners manual. That pressure is determined by the vehicle/tire manufacturer.

The tire pressure on the tire is just for load rating rating purposes, the manufacturer has no idea what vehicle the tire is placed on.
 
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Old 05-16-05, 06:17 AM
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typically...

...the car maker gives you the corrct info for the correct tire application. as long as you are using the same tire size as the vehicle was originally equipped with, you should use the car maker's inflation specs. the inflation specs on the tire are maximum pressures and relate to a full load in the vehicle. you can vary the pressures if you want as long as you stay within the max limit. keep in mind that underinflated tires run hotter than normal (can you say ford explorer/firestone?) and will wear the inside and outside edges prematurely. conversely, overinflated tires will wear the center of the tire more quickly.
 
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Old 05-16-05, 06:21 AM
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Thanks. Will slightly overinflating my tires by 3-5 lbs cause the wear in the center? Also, will doing this give my slighter better mileage?
 
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Old 05-16-05, 06:25 AM
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only one way to tell...

...altho i won't endorse doing it. i agree with TM completely...the car/tire maufacturers spend alot of money to determine optimum operating conditions for the tire...go with the specified pressures and drive as efficiently as possible.
 
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Old 05-16-05, 06:46 AM
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Go with what the carmaker says it should be.
Yes the tires will wear like you say if over inflated.
Fuel mileage will differ neglibly by adding more air to the tires over what it says you should have in them .You won't be able to measure the difference it will be so small of any.
 
  #7  
Old 05-16-05, 06:52 AM
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Originally Posted by teddymines
... Will slightly overinflating my tires by 3-5 lbs cause the wear in the center? Also, will doing this give my slighter better mileage?
Overinflating will cause wear in the center and give you slightly better gas mileage
It reduces your "rolling resistance"
It also reduces your "contact patch" enough to affect handling and braking
...in a bad way

Just 3-5 lbs?
Depends on the tire/vehicle/load/etc.
As mentioned, not really recommened but you'd have to try it to find out
I have vehicles where an extra 5 lbs might not be noticable with some weight in them
And others that would skitter across the road like a skipping stone
 
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Old 05-17-05, 07:19 AM
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Originally Posted by carguyinva
...altho i won't endorse doing it. i agree with TM completely...the car/tire maufacturers spend alot of money to determine optimum operating conditions for the tire...go with the specified pressures and drive as efficiently as possible.
Even with all the time and money spent on determining optimum operating conditions, the manufacturers still inject their personal agendas into the specs.... remember the Firestone/Explorer debacle.... and throw good reason aside.

I always overinflate the tires for a number of reasons. One is to provide a margin of safety should the tires start losing pressure. A soft ride isn't all that important to me, but good handling is. Also, I've never gotten a wear pattern of overinflation from overinflating tires, but many times I've gotten a pattern of underinflation using manufacturer-recommended specs. I always stay within the max recommended pressure on the tire - usually 35 psi.
 
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Old 05-17-05, 09:11 AM
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The oil cahnge place I use always does a good job of checking all the fluids and tire air pressure when performing the oil change heck they even vacumm the interior and clean the winshield. The only problem I have is that there guage is off (inaccurate) they were always letting air out of my tires 3 to 5 pds to match the door placard with their inaccurate gauge. I now take my own air gauge and make them use it, the point being is you need to invest in high quality pressure guage or you will never get proper inflation. Cheap guages lie
 
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Old 05-17-05, 09:28 AM
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Originally Posted by Kestas
...but many times I've gotten a pattern of underinflation using manufacturer-recommended specs.
Gotta say I've noticed this over the years on my "fleet" also
 
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Old 05-17-05, 09:35 AM
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Originally Posted by DNT1
the point being is you need to invest in high quality pressure guage or you will never get proper inflation. Cheap guages lie
Well that must be taken into acount also

I do have a very expensive one that is off by 5 lbs.
It took awhile for me to figure that one out
I figured that one couldn't be off...all the others must be...
 
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Old 05-17-05, 09:55 AM
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I have always over inflated according to vehicle specs and never had a problem. My tires have always worn evenly this way. The ride is a little rougher [only my wife notices] but my tire bill is cheaper. Underinflation is the number one cause of premature tire wear and failure. Of course you never want to exceed the tire rating.
 
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Old 05-17-05, 10:19 AM
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I'll admit that after years of adding 4 psi to manufacturer's recommendations, I simply went to 35 psi for all my fleet... a lot easier to remember.

Tip: If you follow manufacturer's spec's and you have a "fleet" of cars, print out a tiny list that you can tape to your tire gauge. It's the easiest way to keep track of the specs.
 
  #14  
Old 05-17-05, 01:13 PM
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enough already

Enough being so anal about tire presure, gees.
 
  #15  
Old 05-17-05, 01:29 PM
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Originally Posted by chevydrivin
Enough being so anal about tire presure, gees.
I don't see a smiley next to that, but for some of us, it is important with regards to tire life and fuel efficiency.

Thanks for all the tips.
 
  #16  
Old 05-17-05, 04:56 PM
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I have had customers complain about pre-mature ABS activation on new vehicles. Upon diagnosis the problem is often traced to over inflated tire pressure, sometimes, as little a 5 psi is enough. The over inflated tire takes on the “basketball” effect losing its ability to retain a proper tire contact patch with the road surfaces

That’s what an ABS vehicle brings to our attention, the same thing goes on on non-ABS. I can’t stress how important the correct placard pressure is (done with an accurate gauge and after the tire are cold). The suspension, springs, shocks, tire size etc go into arriving at those tire pressures. Using the theory a little extra is a good thing doesn’t always work.


What you think the vehicle manufacture placard pressures have you wasting gas and wearing tires (that they are getting paid under the table by the oil & tire companies).

They want the tire pressure that give the safest handling, best fuel economy and best tire wear. If anything they will push the pressures to give MPG which is very important to them. (Ford/Firestone thing goes against this theroy, they just cheaped out on spec'ing the tire)
 
  #17  
Old 05-17-05, 05:00 PM
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DNT1, ask the guys at the quick oil change place who are letting air out to match the vehicle sticker if they are aware that those figures on the sticker are for "COLD" tires. Chances are when you go in for an oil change, unless the car sits for a couple of hours, the tires will not be "cold".

Side note on tires, tire pressures, etc: I think the ultra-low profile tires that have become so popular lately (why, I have no earthly idea ) were conceived by the tire company engineers to sell more tires. I would wager that a much higher percentage of those dogs on the road are running dangerously underflated (and wearing out/failing much more frequently) than with standard tires. The reason is that because of the ultra low profile, you can literally be running on the rim and unless you look REAL close, you can't tell the difference from a properly inflated one. I can't count the number of failed ultra-low profile tires I've seen and the owners are totally clueless that they've been driving on tire(s) that have next to no air in them. And with a much smaller VOLUME in the tire, the loss of a similar quantity of air will affect the ultra-low profile tires to a greater degree.
 
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