Low Tire Pressure During Frigid Temperatures
Rock Crawling
Joined: Aug 2019
Posts: 392
Likes: 91
From: Plano, Texas
It’s not a question of nitrogen pressure vs air pressure when temps change. That’s the same. Over time less permeates through the tyre. Supposedly. However no-one really keeps that close an eye on their pressures. Then when the temps are lower both drop the In pressure but possibly the air filled tyre was lower to begin with due to the permeation. Again, possibly. I’m not convinced on the benefits of nitrogen, or at least that the benefits aren’t overstated... I’d like to know what difference there really is. And that’s why I wonder if the tyres on my wife’s Kia allow more to permeate than better brands. As both were filled to 40psi in 40degC July but with the same mileage on both hers were all down to 26psi by the time a cold front hit last month. But the tyres on the Disco were barely down when measured the same day.
Recovery Vehicle
Joined: Oct 2018
Posts: 943
Likes: 309
From: Colorado
A little bit of air or nitrogen loss from a small tire will have a larger psi loss than if the same air or nitrogen is lost from a large tire.
I suspect the tires on the D5 are much larger than the kia.
If you lose a few ounces of water from a gallon jug it's a much bigger percentage than that same few ounces lost from a 5 gallon bucket.
I wouldn't assume no one keeps a close eye on their pressure. Maybe there's something wrong with me but I check my pressures on all my vehicles every month. I don't like wearing out tires for lack of such an easy and quick maintenance item. And every month in the fall, they've lost a few psi each and every month in the spring I have to bleed off a little extra psi. Except for one vehicle that had one tire that lost more than the rest - and I found a slow leak.
I suspect the tires on the D5 are much larger than the kia.
If you lose a few ounces of water from a gallon jug it's a much bigger percentage than that same few ounces lost from a 5 gallon bucket.
I wouldn't assume no one keeps a close eye on their pressure. Maybe there's something wrong with me but I check my pressures on all my vehicles every month. I don't like wearing out tires for lack of such an easy and quick maintenance item. And every month in the fall, they've lost a few psi each and every month in the spring I have to bleed off a little extra psi. Except for one vehicle that had one tire that lost more than the rest - and I found a slow leak.
Rock Crawling
Joined: Aug 2019
Posts: 392
Likes: 91
From: Plano, Texas
I was wondering if the rate of loss through permeation would be constant, and if therefore a smaller tyre (as on the Kia) as in less surface area, would possibly lose less. However the opposite, very much so, is true.
I’m curious as to the science behind it or if there is any difference in brand. The tyres Kia our on her car are unknown brands to me hence I’m suspicious of them. But all 4 did all lose air evenly.
I’m curious as to the science behind it or if there is any difference in brand. The tyres Kia our on her car are unknown brands to me hence I’m suspicious of them. But all 4 did all lose air evenly.
Rock Crawling
Joined: Jun 2018
Posts: 460
Likes: 87
From: SF Bay Area, CA
In my experience the construction of the tire very much affected the rate of pressure loss. On the same vehicle and size high load rate LT tires lost less pressure than P rated tires, but the again the thread and sidewalls were much beefier than the P.
Rock Crawling
Joined: Jul 2007
Posts: 448
Likes: 79
From:
Sorry but that's a myth.
Nitrogen is supposed to be slower at leaking through the pores of the rubber so it might be less likely to lose pressure over time, but that's negligible.
It still expands and contracts with temperature. PV=nRT. Can't change the laws of physics. As T (temperature) decreases, either P (pressure) or V(volume) must decrease regardless of the gas involved. Since Volume is constant, then Pressure must decrease.
Also, what you get when you pay for nitrogen is a little bit of nitrogen: Air is already 78 percent nitrogen so maybe you'd get 22 percent. But that's only if you removed all the air from the tire before filling with nitrogen and I doubt tire stores are doing that. And, if you ever top up your tires in the future, you have to do it with nitrogen otherwise you end up with less and less proportion of nitrogen.
You'd be better off to spend your money on a tire gauge and maybe a small compressor and check or top off your tires monthly. Especially in the fall as temperatures drop. In the spring and summer you might be able to just let a little air out each month.
Nitrogen is supposed to be slower at leaking through the pores of the rubber so it might be less likely to lose pressure over time, but that's negligible.
It still expands and contracts with temperature. PV=nRT. Can't change the laws of physics. As T (temperature) decreases, either P (pressure) or V(volume) must decrease regardless of the gas involved. Since Volume is constant, then Pressure must decrease.
Also, what you get when you pay for nitrogen is a little bit of nitrogen: Air is already 78 percent nitrogen so maybe you'd get 22 percent. But that's only if you removed all the air from the tire before filling with nitrogen and I doubt tire stores are doing that. And, if you ever top up your tires in the future, you have to do it with nitrogen otherwise you end up with less and less proportion of nitrogen.
You'd be better off to spend your money on a tire gauge and maybe a small compressor and check or top off your tires monthly. Especially in the fall as temperatures drop. In the spring and summer you might be able to just let a little air out each month.
Of course it’s technically a myth. We could say water compresses, because technically it does, but practically it doesn’t. We are talking in the context of several PSI changes and nitrogen does not change pressure based on temp by any practical standards. It’s why we put it in the tires of our jets. Going from zero to 180kts at high altitude could heat up and blow tires much easier with air. As could rejected takeoffs where there’s massive heat generation. Our takeoff performance would also be much more affected. We use nitrogen for a reason. The shocks of your car??? Nitrogen. Why? Takes heat much better without fluctuations that matter.
We own Land Rovers here. If the $8 for nitrogen is an issue you’re in the wrong spot.
Rock Crawling
Joined: Jul 2007
Posts: 448
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Three Wheeling
Joined: May 2016
Posts: 79
Likes: 7
From: Virginia Beach, VA
TD: you need to go back to school. It is called Boyles LAW for a reason. Pressure changes with temperature for any gas! Nitrogen is a gas. It follows the LAW. Yes, nitrogen is preferred over air, but ambient air is still nearly 80 percent nitrogen. When filling shocks, it is just as easy to load with nitrogen, preferred for the reasons you note, over air. But gas filled shocks are superior because they are better built (to stop gas escape), not just because of nitrogen fill.
Air pressure loss -- not due to change in temperature -- in today's tires is mostly due to quality of the tires and the wheels. Years ago -- a lot of years ago -- I had a brand new BMW 1600 with Continental radials that lost three pounds every week. Frustrated, I insisted that Auto Service Germany in Honolulu replace them with the Pirellis they had in stock (was made easy since I worked there part-time as a tune up tech): problem solved, never had to add air in the Pirellis until the temp dropped below 60*F (doesn't get very cold in HI).
Air pressure loss -- not due to change in temperature -- in today's tires is mostly due to quality of the tires and the wheels. Years ago -- a lot of years ago -- I had a brand new BMW 1600 with Continental radials that lost three pounds every week. Frustrated, I insisted that Auto Service Germany in Honolulu replace them with the Pirellis they had in stock (was made easy since I worked there part-time as a tune up tech): problem solved, never had to add air in the Pirellis until the temp dropped below 60*F (doesn't get very cold in HI).
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