fishnsled Posted October 3, 2011 Report Share Posted October 3, 2011 The other day I took a pressure reading on my trailer tires and they were down a bit. Didn't think it was too bad and drove to a gas station that was easy to get into about a 1/2 hour away. Once there there pressure reading was double what it was previously. Does tire pressure normally change that much? Should you fill your tires to the maximum cold rating? Just curious as I've never see that before and it certainly wasn't a hot summer day. Link to comment Share on other sites More sharing options...
craigdritchie Posted October 3, 2011 Report Share Posted October 3, 2011 You usually inflate to max cold pressure. Air pressure (and temp) will increase once you drive a few kilometres, but it seems excessive to double. My truck uses nitrogen rather than straight air. It doesn't vary in pressure, regardless of the air temp. Link to comment Share on other sites More sharing options...
Billy Bob Posted October 3, 2011 Report Share Posted October 3, 2011 The old nitrogen scam is still alive and well....... Link to comment Share on other sites More sharing options...
mercman Posted October 3, 2011 Report Share Posted October 3, 2011 Nitrogen is used most often when you have tire pressure sending units installed on the tires.There is less pressure variance than air, and less condensation formation, that can affect the senders. But yes, and under inflated tire creates more friction against the ashphalt, causeing them to heat more, therefore expand more.Double? not sure. I guess it depends on what they were before driving on them Link to comment Share on other sites More sharing options...
irishfield Posted October 3, 2011 Report Share Posted October 3, 2011 I wouldn't believe double Will... even if you climbed all the way to the top of the Powder Mountain Pass in Washington State and then took a reading. Link to comment Share on other sites More sharing options...
registerfly Posted October 3, 2011 Report Share Posted October 3, 2011 that sort of rise does seem out of whack. Maybe one of the readings you got was from a faulty gauge unless you used the same both times. should only go up maybe 20% tops. And yes it is normal for tires to fluctuate from 1st thing in the morning, and only takes 10-15 min to reach proper operating temps. Link to comment Share on other sites More sharing options...
lew Posted October 3, 2011 Report Share Posted October 3, 2011 The old nitrogen scam is still alive and well....... But the nitrogen filled tires on my F-150 sure do look purty with the fancy green valve caps. Link to comment Share on other sites More sharing options...
Billy Bob Posted October 3, 2011 Report Share Posted October 3, 2011 Nitrogen is used most often when you have tire pressure sending units installed on the tires. All newer vehicles in the USA have tire pressure sending units because of the Ford Explorer/Firestone Tire fiasco.....but none of these tires as far as I know have nitrogen in them....however, there is one tire dealer here that advertises the great gas savings nitrogen give your vehicle when they add it to their tires upon purchase from them... You would think after all these great gas saving devices that I would have to actually drain gas from my tank....LOL Link to comment Share on other sites More sharing options...
SBCregal Posted October 3, 2011 Report Share Posted October 3, 2011 were you using the same gauge at both places? gas station air pressure gauges are notoriously inaccurate. ryan Link to comment Share on other sites More sharing options...
Billy Bob Posted October 3, 2011 Report Share Posted October 3, 2011 were you using the same gauge at both places? gas station air pressure gauges are notoriously inaccurate. ryan But I'm told they make a great pizza.... Link to comment Share on other sites More sharing options...
SBCregal Posted October 3, 2011 Report Share Posted October 3, 2011 Link to comment Share on other sites More sharing options...
Billy Bob Posted October 3, 2011 Report Share Posted October 3, 2011 http://ontariofishingcommunity.com/forums/index.php?showtopic=57427&pid=627332&st=0entry627332 Link to comment Share on other sites More sharing options...
muskymike Posted October 3, 2011 Report Share Posted October 3, 2011 But I'm told they make a great pizza.... :rofl2: Link to comment Share on other sites More sharing options...
John Bacon Posted October 3, 2011 Report Share Posted October 3, 2011 Actually, Air is 80% nitrogen. Nitrogen does indeed change pressure with temperature, that's a law of all gases. What pure nitrogen helps with is pressure loss due to diffusion - nitrogen leaks less quickly through rubber than oxygen, so hence 100% Nitrogen loses pressure less quickly than 80% Nitrogen/20% Oxygen...at least that's what the guys who sell the nitrogen say! If that is true then when my tire lost pressure would it be because the oxygen leaked out... and the nitrogen would still remain? If so, would the nitrogen content increase and approach 100% as I continnually replaced the lost oxygen content with and 80/20 nitrogen/oxygen mixture? That would be cheaper than actually paying for the nitrogen. Just asking. Link to comment Share on other sites More sharing options...
BillM Posted October 3, 2011 Report Share Posted October 3, 2011 No way the pressure doubled. You might see a few psi at most (10% as mentioned before) when hot vs cold. Link to comment Share on other sites More sharing options...
Fisherman Posted October 3, 2011 Report Share Posted October 3, 2011 I'm guessing they like to use nitrogen for tires/wheels using tpms for the sole reason that there's no oxygen to speed up the corrosion inside the tire for the tpms components. Other than that, maybe a nitrogen molecule is larger in size and can't leak out as easy as an oxygen molecule. Link to comment Share on other sites More sharing options...
mercman Posted October 3, 2011 Report Share Posted October 3, 2011 Don't mind the 'merican. Is that what he is I call him a gun toting redneck, but he likes it when i call him that. Link to comment Share on other sites More sharing options...
bigbuck Posted October 3, 2011 Report Share Posted October 3, 2011 SCAM!!! The nitrogen used is between 90-95% pure nitrogen. The rest is good old oxygen and trace gases. The air we breathe is between 78-80% nitrogen so really, I would not pay for it, if it was free, they can knock themselves out. Link to comment Share on other sites More sharing options...
fishnsled Posted October 4, 2011 Author Report Share Posted October 4, 2011 I have a digital tire gauge and it was at 39psi. Went to the gas station and use the gauge on hose and read just shy of 80psi. Grabbed my gauge and checked both tires on trailer and one was 77psi and the other was 76psi. I usually run the tires at 45psi and are cold rated at 50psi. Some good info guys and a few laughs. Link to comment Share on other sites More sharing options...
vinnimon Posted October 4, 2011 Report Share Posted October 4, 2011 No way the pressure doubled. You might see a few psi at most (10% as mentioned before) when hot vs cold. I just had this discussion today with one one of our brokers. Variance in tire perssure, from season to season and cold versus hot tire pressure(just coming off the rd) For example the tires(commercial wise 11 r 22.5) is rated at 105 t0 110 cold max presure. A few I know will down rate them to 95 psi cold in the warm weather. After coming back from a trip, there is a 10 to 12% increase. In the cold part of the season its usually brought to 100 to 105 psi. The most extreme pressure reading ive come across, at hot pressure was 135. During some of the hottest days of the year. I variate tire pressures pending the seasons and longevity of the trip im on. But never seen double. Link to comment Share on other sites More sharing options...
Stumps Posted October 4, 2011 Report Share Posted October 4, 2011 I have a digital tire gauge and it was at 39psi. Went to the gas station and use the gauge on hose and read just shy of 80psi. Grabbed my gauge and checked both tires on trailer and one was 77psi and the other was 76psi. I usually run the tires at 45psi and are cold rated at 50psi. Some good info guys and a few laughs. Good possibility the Digital was stuck or reading a saved reading . Tire gauges are never very accurate . Link to comment Share on other sites More sharing options...
BillM Posted October 4, 2011 Report Share Posted October 4, 2011 Any chance the OP was reading Kpa and not PSI on the tire gauge? :) Link to comment Share on other sites More sharing options...
fishnsled Posted October 4, 2011 Author Report Share Posted October 4, 2011 Any chance the OP was reading Kpa and not PSI on the tire gauge? :) Checked for that as well but it was at psi. My buddy that was with me drives trucks for a living and has never seen that kind of a difference before in his 20+ years of driving either. Checked with a buddy who is a mechanic and he's scratching his head too. Thought I'd put it up here and see what the experts had to say. Link to comment Share on other sites More sharing options...
Rattletrap2 Posted October 4, 2011 Report Share Posted October 4, 2011 Actually, Air is 80% nitrogen. Nitrogen does indeed change pressure with temperature, that's a law of all gases. What pure nitrogen helps with is pressure loss due to diffusion - nitrogen leaks less quickly through rubber than oxygen, so hence 100% Nitrogen loses pressure less quickly than 80% Nitrogen/20% Oxygen...at least that's what the guys who sell the nitrogen say! Sorry, But I have to disagree! The reasoning behind using Nitrogen in tires is directly linked to it's "inert" properties. While not purely inert, it is virtually so at the temperatures and pressures used in tires. The air we breath is considered to be 78% Nitrogen, 20.9% oxygen, and the remainder (approx. 1%)is other gases such as CO2, Argon, etc. Commercial Aircraft have always used Nitrogen in their tires so that the pressure at 40,000 feet would not be that much different from the pressure on the runway in Saudi Arabia. The "scam" part comes from the tire shops that have discovered it fashionable to sell it to people at inflated prices. Those of us with a "ready" access to it have been filling our tires, blowing out drains, and many other uses for decades! Another scam is when they try to sell you "Extra Dry" grade at the gas suppliers! They charge a premium price and guaranty the moisture content or lack there of. The responsibility is on the customer to prove it! In most cases, these cylinders are filled off the same header as all the rest. Without laboratory analysis, how can you tell? Link to comment Share on other sites More sharing options...
Billy Bob Posted October 4, 2011 Report Share Posted October 4, 2011 Don't mind the 'merican. Ya, never mind the 'merican but it takes 29+ posts for you Cunuks to figure out how much air to put in your tires....... Us Rednecks don't even need a gauge to do that.... Link to comment Share on other sites More sharing options...
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