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Old 01-16-2015, 08:35 PM   #15
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Quote:
all of my tires are measuring about 4psi lower that yesterday afternoon.
To me, this is the key statement. Establish a baseline, and if they all do the same thing, you are probably OK. If one drops significantly more than the others, there may be a problem.
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Old 01-16-2015, 09:05 PM   #16
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Fill the tires with dry nitrogen so you don't have to worry about a few pounds of pressure change when the temperature drops. Its cheaper than Prozac to quell the anxiety! LoL!!
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Old 01-16-2015, 09:08 PM   #17
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I use 80% nitrogen in my tires, it's free in Ohio.
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Old 01-16-2015, 09:21 PM   #18
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Originally Posted by Tireman9 View Post
Nope. If you read the literature from tire companies they refer to atmospheric temperature not laboratory temperature.

Normally most tire pressure will change 2% for every 10°F change. You can read the Science in THIS post.
So let me see if i have this right tp 80 at 75 would equal 65 at 55, so do i fill back to 80 when temp is 55, as outside temp will climb during the day or what
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Old 01-16-2015, 10:21 PM   #19
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Originally Posted by jmckinley View Post
I use 80% nitrogen in my tires, it's free in Ohio.

Maybe this post is tongue-in-cheek. Regular atmosphere IS nearly 80% nitrogen.
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Old 01-16-2015, 10:39 PM   #20
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Folks ... I think we are all making WAY too much of this. The way I think of it, the biggest danger to tires is running them at too low a pressure for their loading. The point of checking the pressure "cold" is that from there the pressure will only go up (as temperature rises, either due to ambient temperature, sunlight , or running on the things). The basic point is you NEVER want to run them below that minimum . Thus the "cold inflation pressure" is basically the "idiots guide to keeping the pressure from getting too low". Follow that guide and you will be fine (because from the cold pressure the real time pressure will just go up ). If on the other hand you can have real-time pressure measurements, like what TPMS Gives you, then do the adjustments you need to do to keep that pressure from ever dropping below that minimum for your loading. Back in November I made a run from Missouri to minnesota: temperature varied from 40 degrees at the start to something like -5 degrees at the end. My tire pressures were fine when I started, BUT my worry was IF I stopped rolling for too long my tires would cool off and fall below my minimum. TPMS kept me clear on what my tire pressures were doing (TALK about incentive to keep putting miles behind me. :-). ). ... BUT this was a case where the standard rule of checking the pressures only I n the morning would have failed me if I had stopped for too long ...
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Old 01-16-2015, 11:16 PM   #21
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Maybe this post is tongue-in-cheek. Regular atmosphere IS nearly 80% nitrogen.

That was my point. Selling nitrogen to unsuspecting consumers is almost criminal. Almost as bad as selling bottled tap water for $8 per gallon.
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Old 01-16-2015, 11:32 PM   #22
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Originally Posted by Tireman9 View Post
Camato5 is close. You don't need to sit for 12 hours.

"Cold" inflation means:
1. Not having been driven more than 1/4 mile in previous 2-3 hours.
and
2. Not being in direct sunlight for the previous 2-3 hours

We are not talking about a Chem Lab or Physics Lab experiment where we set temperature and atmospheric pressure to some special "standard" condition. We mean the tire is at the same temperature as the air outside.

Now some will take this to an extreme and try and ask about being parked at 12,000 feet in sub zero conditions when they are planning on driving to the bottom of Death Valley where it is 130°F. Under normal conditions in normal travel there are no special adjustments for temperature or elevation that need to be considered. I have covered both temperature and elevation in posts on my tire blog.

If you are under the extreme conditions mentioned above pleas PM me and we will work out a plan for proper inflation procedure.
Guy lives up to his name. This is spot on.

The rule of thumb is there's a 1PSI change for every 10* of temperature change and it's pretty linear with the pressure and temperature ranges we work with.

So, for easy figures, if you set your pressure at 50 while it's 70* and the next day it's in the 40s as you had, 2-3PSI is normal. And in the grand scheme of things isn't detrimental. Who knows, you could end up in southern Florida and find yourself over 2-3PSI which, again, isn't detrimental.

Now once you cross 5PSI then it's worth touching up but just check them in the mornings, every tank or weekly, whatever your personal habit is, set them to the cold spec that fits you best and don't worry about it.
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Old 01-17-2015, 05:14 AM   #23
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Talking about 2 or 3 psi in 100psi is somewhat meaningless given the specified accuracy of any normal means of measuring the pressure. TPMS accuracies are worth having a look at because they are often nothing to write home about either.


"Fill the tires with dry nitrogen"

Can't be done.
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Old 01-17-2015, 06:52 AM   #24
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Originally Posted by Betr2Trvl View Post

A simple rule of thumb is 1lb of tire pressure for every 10 degrees. For instance, if your took your "cold" tire pressures (not driven on all day for instance) in the afternoon and it is 70 degrees, and then you check them in the morning when it is 40 degrees, you'll see about a 3lb drop (just as the op and Randy noted).
You are off by 1 lb Unless the tire needs 50 PSI or less then your 1 lb rule would work. But not many MH tires use 50 PSI or less.

Goodyear says.
The Ups and Downs of Inflation
A 10° F air temperature change will:
Change inflation pressure 2% in the same direction.
That’s an increase of 2 psi on a 100 psi tire when the temperature increases 10° F
“Working Inflation” increases 5-15 psi when a tire warms up


Atmospheric pressure changes .48 psi for every 1,000 feet change in altitude. If a tire has 100 psi at sea level, your gauge will read .5 psi higher for every 1,000 foot increase in altitude


Inflation pressure has the most drastic effect on tire wear
Correct inflation is key to satisfactory tire performance
Wear rate is optimal when the tire operates at
the correct inflation pressure
Underinflation is worse than overinflation because:
Tires wear unevenly
Generates more heat from overdeflection


When traveling at 65 mph vs. 55 mph, tires will experience a 15% tread life penalty (30% at 75 mph)
Trucking fleets report fuel economy losses of about one mpg for every ten mph over 55 mph(a 15% loss)
Longer breaking distances (SAFETY ISSUE!)
Reduced handling ability (SAFETY ISSUE!)
More fuel stops due to reduced fuel economy
Tire load-carrying capability decreases as speed increases




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Old 01-17-2015, 07:11 AM   #25
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Some good info here. Tires don't fail because they are 4 lbs low, they fail because they are grossly low, as a general rule. The air pressure gauge you use is going to have be a very good one to be better than 3% accurate, or 3 psi at 100psi. That means you don't know whether you have 97psi or 103psi, or somewhere in-between, it's close enough.
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Old 01-17-2015, 07:54 AM   #26
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Originally Posted by Tireman9 View Post
Camato5 is close. You don't need to sit for 12 hours.

"Cold" inflation means:
1. Not having been driven more than 1/4 mile in previous 2-3 hours.
and
2. Not being in direct sunlight for the previous 2-3 hours

We are not talking about a Chem Lab or Physics Lab experiment where we set temperature and atmospheric pressure to some special "standard" condition. We mean the tire is at the same temperature as the air outside.

Now some will take this to an extreme and try and ask about being parked at 12,000 feet in sub zero conditions when they are planning on driving to the bottom of Death Valley where it is 130°F. Under normal conditions in normal travel there are no special adjustments for temperature or elevation that need to be considered. I have covered both temperature and elevation in posts on my tire blog.

If you are under the extreme conditions mentioned above pleas PM me and we will work out a plan for proper inflation procedure.
Thanks tireman9 I was not sure of what was considered a cold tire but knew it had to do with the tire not moving for a certain amount of time and sitting in the same ambient temperatures. So less than 1/4 of a mile and 2 to 3 hours is the correct answer.. I did KNOW I wasn't going to pull over every time the temp changed 10 degrees ha.
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Old 01-17-2015, 09:18 AM   #27
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sorry guys i can;t seem to add right my bad 2% of 80 is 1.6 not 16.its a bitch to get old
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Old 01-17-2015, 09:22 AM   #28
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You're going to drive yourself crazy chasing your tire pressure. I usually add air to my tires once a year in the spring and don't use a tpms. Never had a problem, always check them before a long teip and usually never have to add air.

Cheers!
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