Tire pressure obsession

[Grumpy Bear]

5 hours ago, draperfish said:

 When my truck as been sitting with the sun shinning on one side in the morning and those pressures are 2 or 3 pounds higher than the other side it bugs me too. 

This one was interesting, honest and absolutely on point. 

 

The rule of thumb is for every 10° Fahrenheit change in AMBIENT air temperature, tire pressures will change about 2%. That's 0.7 psi per 10 F for a 35 psi target pressure. In our area we have a daily high to low of about 15 degrees or about 1 psi day to night. 

 

PV=nRt  Who ever said N2 is no different than air needs to look at the gas law more closely. Here's a link for that. 

 

https://www.khanacademy.org/science/chemistry/gases-and-kinetic-molecular-theory/ideal-gas-laws/v/ideal-gas-equation-pv-nrt

 

Sunny side to shade side can be 2 or 5 psig or MORE. So what does that mean? Check your pressures in the morning before sunrise and outside after sitting all night. Your pressure monitor will equalize in about a half hour of highway driving.  

 

I have 85K miles of records on Pepper and I find in her case that 3 psi will affect fuel and tire wear measurably. 5 psi is worth near 10% in fuel economy. 

 

 

[NWI Denali]

13 hours ago, 1SLOW1500 said:

why you laugh. Really get the air out and have nitrogen put in. never deal with it again.

Air is 78% nitrogen...

[1SLOW1500]

Air is 78% nitrogen...

I don't know but it works great. Never a issue in 12 years.

Sent from my SM-N950U using Tapatalk

[gearheadesw]

Nitrogen in the tires, is so people that don't know any better think they have to go back to the dealership to nitrogen up their tires. It's a ploy.

[diyer2]

Not worth the hassle to me.

Besides where we are now getting nitrogen is a 120 mile trip .

Air works.

 

[jadatis]

16 hours ago, Cupton said:

 

At what pressure fluctuation do you all find yourselves out there in the cold (or heat) adjusting your tire pressure due to temperature change? Is it a 1-2 PSI change from your normal pressure? More or less than that?

 

Reason I ask is that it’s a little colder today and noticed I was down to 34 PSI and was kind of stressing over it. I was about to go top them off at 35 PSI and stopped myself due to it only being a 1 PSI difference and it warming up for a few days before it gets colder again.

 

Just curious what PSI change needs to happen for all of you to go out and freeze (or sweat) your butts off to top off or let air out of your tires.

 

Dont worry about the lower pressure when cold outside.

Pressure -advice is to give the tire a deflection that wont overheat any part of it when driving the speed constantly for wich it is determined.

That it warms up inside tire by driving and by that higher pressure,  is all taken into account.

Pressure is determined for 18 degr C/65 degr F cold measured so when inside tire and outside tire same temperature.

When colder , lower pressure so more deflection, so more heatproduction, but also more cooling down because of The larger temperature differences between rubber and inside and outside air.

So when you calculate the measured pressure back to 18 degr C/65 degr F , or when you yust filled it at that temp, within a sertain ranche of temperature outside, warming up and cooling down of rubber stays in balance, so not any part of tire reaches a to high temperature.

This means that you sertainly must not lower the pressure to determined advice  when hot outside , the tire needs the lesser deflection the higher pressure gives, to produce lesser heat, because cooling down is also worse because of the smaller temperature differences. But when colder you dont need to highen up.

You may do so when colder, to give lesser deflection so lesser fuel-consumption, or  to give  the car the same riding experiënce as when 18 degr C/65 degr F.

Some write its 20 degr C/68 degr F , but difference is that small in pressure , that same system goes.

[Nick The Great]

I think the OP needs more serious things to worry about in his life than a 1 psi drop in tire pressure.    

 

I don't buy the Nitrogen being much better than regular air either.  Though I will say, I bought this truck in April 2017, and I think just now added air a few weeks ago.  Didn't touch it last winter, and we had some cold days.  

 

 

[Donstar]

2 hours ago, NWI Denali said:

Air is 78% nitrogen...

"Fun fact" as Sheldon Cooper would say!   The human brain is 73% water...

I've used "nitrogen" in my tires for several years and find that my pressure remains pretty constant between rotations.  Also, most service stations around me have coin operated "air".  Costco tops up nitrogen for free.

[duquephart]

5 minutes ago, Donstar said:

"Fun fact" as Sheldon Cooper would say!   The human brain is 73% water...

I've used "nitrogen" in my tires for several years and find that my pressure remains pretty constant between rotations.  Also, most service stations around me have coin operated "air".  Costco tops up nitrogen for free.

 

Watch out for dealers delivering cars with "nitrogen fill" for $200 - $300!

[Cupton]

Thanks all for your responses. As I figured yesterday, stressing over 1-2 PSI isn't worth it. I'll tuck the compressor further back into the garage and bring the snow blower up front and a little closer.  ;)

[Grumpy Bear]

I don't use nitrogen in my tires. Cost, availability or as one poster says, 'hassle'. That said the science is sound even if the benefit is minor. Dismissing/denying  something because one doesn't understand it or finds it inconvenient doesn't change the science. 

 

51 minutes ago, jadatis said:

Don't worry about the lower pressure when cold outside.

Pressure -advice is to give the tire a deflection that wont overheat any part of it when driving the speed constantly for which it is determined.

 

True and notable but not the entire story and dangerous. Deflection is also resistance to motion. Ever try to move a wheelbarrow full of dirt with a nearly flat tire? Deflection is also wear not just in general but specific to the area of the tires foot print. By your logic I can inflate my tires in my 68F  heated garage I'll be fine when it's -32 F outside. PV=nRT (the basis for the 2% per 10F rule of thumb) says that will be a 20 psi loss of pressure and while it is true that driving increases tire pressure it isn't true it's 20 pounds worth. 

 

What the OP is attempting to understand isn't IF temperature makes a difference or IF there is merit in nitrogen over air but at what point should one be concerned enough to do something about it. 

 

I can only offer my experience. The answer is 'depends'. Look, I monitor my tire pressures every time I get in the truck and then I ask myself the basic question a five year old would ask...does that reading make sense? Tire pressure reads 4 psi higher on the sunny side at noon...yea that makes sense. Is today 'average'? Is this a one day cold snap or unusually hot day or is this a seasonal shift that is likely going to stick around? I use a 5% rule...two or three pounds cold pressure as a point of adjustment IF the conditions seem likely to be around awhile and measured under the same conditions. Like first thing in the morning while the sun is low. 

 

If you make your TPMS reading a habit you can learn allot about your truck/car. If you let it teach you the worry goes away and the education becomes a tool that let's you enhance your experience. 

 

 

[swathdiver]

I endeavor to keep them all the same and adjust the tires just after sunup after sitting all night.  I've had the sun heat up one side 2 psi more than the other while sitting in the driveway and while on the highway.  New home faces east so the RF tire gets the most sun now from a cold start.  The truck is a bit jittery after a cold start and after some miles the tires heat up and are all even again.  I run LTs which are more greatly affected by temperature than P-Metrics.  3 psi or more difference per side at speed and it feels like you're driving in two different directions or speeds!  

 

With the monitor on the DIC, I can get them all to within a pound of each other.  Combining that with the Tech2, I can get them all within 1/2 psi of each other.  Runs much smoother after putting in that effort.  

[Capt Bob]

I use a similar method myself. Get the truck level on the driveway (as close as possible by eye) and check pressure in the early AM before the sun clears the house (truck still in shade). Truck has sat overnight in this spot. Nothing as high tech other than an old mechanical aircraft tire gauge but by getting all tires to 36psi my monitor reads 35psi consistently at that point.

[pronstar]

Excellent read on nitrogen filled tires...it ain’t really about the nitrogen.

 

 

https://jalopnik.com/heres-the-deal-with-nitrogen-filled-tires-1795659391

 

 

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[aseibel]

2 hours ago, pronstar said:

Excellent read on nitrogen filled tires...it ain’t really about the nitrogen.

 

 

https://jalopnik.com/heres-the-deal-with-nitrogen-filled-tires-1795659391

Good article. It explains exactly why I'm not going to pay for nitrogen when 78% nitrogen is free.

 

"Is it worth it? For normal driving, probably not. The advantages, while real, are still really very miniscule."