Not having driven for 4 hours has appeared in more than one owners manual.
"Cold" tire pressure.
- Thread starter Jarpin
- Start date
The reason people push nitrogen is that it is more temperature stable.
They started using it about the time vehicles came out with TPMS's.
Pretty sure dealers started doing it just to get rid of the nuisance low tire warnings ( and s***w people out of the typical $29.00 charge)
From what I have seen. A tire that has sat overnight around 32f should be good at 32psi..... believe it or not.
I try to set mine in warmer weather and will go 35psi ~70-80f.
Driving on the highway in the summer I can see 39-40 psi after they heat up... at highway speed....about 30min.
Measuring cold pressure is for reason , that its the most reliable. Goal of recomended pressure, is to give the tire a warm pressure, so deflection , that wont overheat any part of tire, when driving the speed its determined for.
But warm is unreliable to measure, howmuch has it cooled down already since you stopped, and what speed did you drive.
Cold pressure is when the temperature of the gascompound ( air or more Nitrogen) is the same as outside the tire, so ambiënt temperature.
at the end when temp in and out tire are almost the same, cooling down goes verry slow, because of low temp differences.
Now this not driven for hours has become the criterium in time, but that in and out tire same temp still is the goal.
Reason is that with temperature change the pressure changes.
But a few degr higher in tire then outside, wont give that much other pressure, so use your own common sense for that.
Now recomended pressure is for ambiënt temperature meanth to be filled, is the general rule.
But my idea is that its for an average ambiënt temperature meanth, and I keep it at 68 degrF/20 degr.
So on a hot day of say 100degrF you need higher pressure to give lesser deflection, so lesser heatproduction at same speed. Because cooling down of tire is also less because of lesser temperature difference between rubber and in and outside tire gascompound.
So you must never lower the pressure to recomended on a 100degrF day, you risk overheated tires, and only once is enaugh to give little internal cracks, that can cource in time tire failure.
Its the temperature of rubber that destroys the tire, not the high pressure.
Tires are desighned and tested to can stand a pressure of 2 to 3 times the reference-pressure,( SL P-tire 35 or 36psi, Extraload /reinforced/XL 41 or 42 psi referencepressure)
on a cold day of say 40 degrF, the other way around, more heatproduction , but also more cooling down, so rubber still wont reach it critical temperature.
then the lower pressure does not need to be highened up for reasons of safety, but you may do it for roadhandling and fuelsaving.
Nature aranges this itself, warmer temp in tire gives higher pressure, and that is most likely enaugh.
Made a list in wich you can search back the pressure you determined to fill( at 68 degrF),and the degrF change / psi. Then those who have tmps can remember that for their pressure used, and calculate by head accurate enauch for the goal, the temperature in tire whhile driving to check the temperature reading, external sensors temp-reading is not accurate because it measures the temp at the end of the valve.
But you can also use it to compensate the recomended pressure at different temp then 68 degrF. O r to play with in this topic, to see what the effect is on the pressure-reading, on a not totally cooled down tire.
This is my idea, and already found some confirmation on internet, but was burned down on it on RV forum, especially about the lower pressure allowed for lower temperature.
So read and yudge it using your own common sense.
Here it is, rounded to 0.5 degrF, because acurate enaugh, and easyer to remember.
Pressure at 68degrF/ degrF/psi
20 psi/ 15,5F/psi
21 psi/ 15F/psi
22 psi/ 14,5F/psi
23 psi/ 14 F/psi
24 psi/ 13,5F/psi
25 psi/ 13,5F/psi
26 psi/ 13 F/psi
27 psi/ 12,5 F/psi
28 psi/ 12,5 F/psi
29 psi/ 12 F/psi
30 psi/ 12 F/psi
31 psi/ 11,5 F/psi
32 psi/ 11,5 F/psi
33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/
But warm is unreliable to measure, howmuch has it cooled down already since you stopped, and what speed did you drive.
Cold pressure is when the temperature of the gascompound ( air or more Nitrogen) is the same as outside the tire, so ambiënt temperature.
at the end when temp in and out tire are almost the same, cooling down goes verry slow, because of low temp differences.
Now this not driven for hours has become the criterium in time, but that in and out tire same temp still is the goal.
Reason is that with temperature change the pressure changes.
But a few degr higher in tire then outside, wont give that much other pressure, so use your own common sense for that.
Now recomended pressure is for ambiënt temperature meanth to be filled, is the general rule.
But my idea is that its for an average ambiënt temperature meanth, and I keep it at 68 degrF/20 degr.
So on a hot day of say 100degrF you need higher pressure to give lesser deflection, so lesser heatproduction at same speed. Because cooling down of tire is also less because of lesser temperature difference between rubber and in and outside tire gascompound.
So you must never lower the pressure to recomended on a 100degrF day, you risk overheated tires, and only once is enaugh to give little internal cracks, that can cource in time tire failure.
Its the temperature of rubber that destroys the tire, not the high pressure.
Tires are desighned and tested to can stand a pressure of 2 to 3 times the reference-pressure,( SL P-tire 35 or 36psi, Extraload /reinforced/XL 41 or 42 psi referencepressure)
on a cold day of say 40 degrF, the other way around, more heatproduction , but also more cooling down, so rubber still wont reach it critical temperature.
then the lower pressure does not need to be highened up for reasons of safety, but you may do it for roadhandling and fuelsaving.
Nature aranges this itself, warmer temp in tire gives higher pressure, and that is most likely enaugh.
Made a list in wich you can search back the pressure you determined to fill( at 68 degrF),and the degrF change / psi. Then those who have tmps can remember that for their pressure used, and calculate by head accurate enauch for the goal, the temperature in tire whhile driving to check the temperature reading, external sensors temp-reading is not accurate because it measures the temp at the end of the valve.
But you can also use it to compensate the recomended pressure at different temp then 68 degrF. O r to play with in this topic, to see what the effect is on the pressure-reading, on a not totally cooled down tire.
This is my idea, and already found some confirmation on internet, but was burned down on it on RV forum, especially about the lower pressure allowed for lower temperature.
So read and yudge it using your own common sense.
Here it is, rounded to 0.5 degrF, because acurate enaugh, and easyer to remember.
Pressure at 68degrF/ degrF/psi
20 psi/ 15,5F/psi
21 psi/ 15F/psi
22 psi/ 14,5F/psi
23 psi/ 14 F/psi
24 psi/ 13,5F/psi
25 psi/ 13,5F/psi
26 psi/ 13 F/psi
27 psi/ 12,5 F/psi
28 psi/ 12,5 F/psi
29 psi/ 12 F/psi
30 psi/ 12 F/psi
31 psi/ 11,5 F/psi
32 psi/ 11,5 F/psi
33 psi/ 11 F/psi
34 psi/ 11 F/psi
35 psi/ 10,5 F/psi
36 psi/ 10,5 F/psi
37 psi/ 10 F/psi
39 psi/ 10 F/ps
40 psi/ 9,5 F/psi
42 psi/ 9,5 F/psi
43 psi/ 9 F/psi
45 psi/ 9 F/psi
46 psi/ 8,5 F/psi
49 psi/ 8,5 F/psi
50 psi/ 8 F/psi
53 psi/ 8 F/psi
54 psi/ 7,5 F/psi
58 psi/ 7,5 F/psi
59 psi/ 7 F/psi
63 psi/ 7 F/psi
64 psi/ 6,5 F/psi
70 psi/ 6,5 F/psi
71 psi/ 6 F/psi
77 psi/ 6 F/psi
78 psi/ 5,5 F/psi
86 psi/ 5,5 F/psi
87 psi/ 5 F/psi
96 psi/ 5 F/
Allow me to answer the second question first: Why is the proper inflation pressure not tied to temperature? Why is it always at ambient temperature?
Because load carrying capacity of tires is tied to the stiffness of the sidewalls - and that stiffness is tied to inflation pressure, not temperature - and since you ALWAYS want enough load carrying capacity, you always want the inflation pressure adequate for whatever ambient conditions you are operating at. Ergo, set the pressures for the ambient conditions the tire is going to be operated in.
Another tidbit: Inflation pressure isn't all the critical, but it is better to be high than low.
So onto the second question: How quickly does inflation pressure build up? Even 10 minutes of normal driving will elevate pressures - and it takes about an hour and a half for tires to cool - BUT AGAIN, it is not that critical! If you driving 10 minutes and set the pressure 2 or 3 psi too high, NOTHING BAD IS GOING TO HAPPEN! You can later set the pressures back down if you want to.
As was stated above, normal pressure build from cold to hot is supposed to be no more than 10%. On a passenger car tire that is 3 psi, but on an 80 psi truck or trailer tire that's 8 psi.
And just so you know, the burst pressure of tires is many times the max pressure - meaning that passenger car tires burst at over 100 psi and 80 psi truck and trailer tires burst over 200 psi. So going over the max pressure isn't as big a deal as some people make it out to be.
So why do folks say not to exceed the max pressure? Because they don't want idiots inflating 35 psi passenger car tires to 80 psi truck and trailer tire pressures thinking that will be OK!
Now the bit about changes in pressure due to ambient temperature. The rule of thumb for passenger car tires is 1 psi for every 10°F. For truck and trailer tires that rule is 2% for every 10°F.
So if you are setting the pressure for your car in a 70°F garage and it's going to be 20°F tomorrow, set them 5 psi high. For an 80 psi truck or trailer tire, that would be 8 psi high.
When I say nothing bad is going to happen if you set the pressures too high, I'm talking about 10% or so high. I'm also saying that nothing terrible is going to happen to the traction, handling or wear. Just as an example, tire wear is more affected by alignment than it is inflation pressure. Even driving style has more affect on tire wear than inflation pressure does.
Hope this clears things up.
Because load carrying capacity of tires is tied to the stiffness of the sidewalls - and that stiffness is tied to inflation pressure, not temperature - and since you ALWAYS want enough load carrying capacity, you always want the inflation pressure adequate for whatever ambient conditions you are operating at. Ergo, set the pressures for the ambient conditions the tire is going to be operated in.
Another tidbit: Inflation pressure isn't all the critical, but it is better to be high than low.
So onto the second question: How quickly does inflation pressure build up? Even 10 minutes of normal driving will elevate pressures - and it takes about an hour and a half for tires to cool - BUT AGAIN, it is not that critical! If you driving 10 minutes and set the pressure 2 or 3 psi too high, NOTHING BAD IS GOING TO HAPPEN! You can later set the pressures back down if you want to.
As was stated above, normal pressure build from cold to hot is supposed to be no more than 10%. On a passenger car tire that is 3 psi, but on an 80 psi truck or trailer tire that's 8 psi.
And just so you know, the burst pressure of tires is many times the max pressure - meaning that passenger car tires burst at over 100 psi and 80 psi truck and trailer tires burst over 200 psi. So going over the max pressure isn't as big a deal as some people make it out to be.
So why do folks say not to exceed the max pressure? Because they don't want idiots inflating 35 psi passenger car tires to 80 psi truck and trailer tire pressures thinking that will be OK!
Now the bit about changes in pressure due to ambient temperature. The rule of thumb for passenger car tires is 1 psi for every 10°F. For truck and trailer tires that rule is 2% for every 10°F.
So if you are setting the pressure for your car in a 70°F garage and it's going to be 20°F tomorrow, set them 5 psi high. For an 80 psi truck or trailer tire, that would be 8 psi high.
When I say nothing bad is going to happen if you set the pressures too high, I'm talking about 10% or so high. I'm also saying that nothing terrible is going to happen to the traction, handling or wear. Just as an example, tire wear is more affected by alignment than it is inflation pressure. Even driving style has more affect on tire wear than inflation pressure does.
Hope this clears things up.
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On my 2002 Jaguar XKR just a slight increase of tire pressure does significantly affect the tire wear.
The factory manual gives two cold specifications for tire pressure:
1) 26 F / 28 R - maximum comfort
(& under 100 mph)
or
2) 32F / 34 R - labeled “normal”
(for speeds over 100 mph)
If using the “normal”, and higher specified tire pressure most owners report that the tires will prematurely wear first in the middle of the tread. A classic sign of over-inflation.
So, as a group, most owners are dialing down the tire pressure to a midpoint between the two factory specifications. That has cured the early wear in the center of the tread for me, and others have reported similar results. Most owners are using the same brand and type of tires that came as standard equipment when new, the Michelin Pilot Sport. I’ve experimented with several other brands and have settled on the Michelins.
By the way, The car is pretty heavy for a small vehicle, 4,431 lb fully loaded.
Back to the “cold temperature” topic, I have an inexpensive tire temperature monitoring system installed. Independent of ambient air temperature the tire temperature will generally change upward after 2 or 3 miles of driving. But it takes a hour or more of driving to max out.
If there has been a dramatic ambient air temperature shift I’ll check and adjust the tire pressure before the days first drive. Otherwise I just check it via the monitoring system occasionally
Z
The factory manual gives two cold specifications for tire pressure:
1) 26 F / 28 R - maximum comfort
(& under 100 mph)
or
2) 32F / 34 R - labeled “normal”
(for speeds over 100 mph)
If using the “normal”, and higher specified tire pressure most owners report that the tires will prematurely wear first in the middle of the tread. A classic sign of over-inflation.
So, as a group, most owners are dialing down the tire pressure to a midpoint between the two factory specifications. That has cured the early wear in the center of the tread for me, and others have reported similar results. Most owners are using the same brand and type of tires that came as standard equipment when new, the Michelin Pilot Sport. I’ve experimented with several other brands and have settled on the Michelins.
By the way, The car is pretty heavy for a small vehicle, 4,431 lb fully loaded.
Back to the “cold temperature” topic, I have an inexpensive tire temperature monitoring system installed. Independent of ambient air temperature the tire temperature will generally change upward after 2 or 3 miles of driving. But it takes a hour or more of driving to max out.
If there has been a dramatic ambient air temperature shift I’ll check and adjust the tire pressure before the days first drive. Otherwise I just check it via the monitoring system occasionally
Z
Actually, on the newer G series BMW, it is tied to temperature. The door jamb sticker is only because it’s required. We go by the settings in the iDrive which accounts for different tire sizes, max vehicle speed, and temperature.
I love my that new Indian Ford has readout graphic per tire. I look at that before setting off so I don't have to perform a walk around
visual check. Yes I do this every trip. With the advent of cold weather, I leave my tires a bit low. Smooths the ride and traction seems improved in snow and ice as the oil in the shocks is very viscous when cold.
Yesterday, with ambient at 26deg F, the DIC readout was 29psig starting out and the tires were at 31psig when i got to the grocery store 7 miles away down a hilly and winding road. It will be 14 deg F this morning. Maybe stay in
ps: I would never attemp to set the tires to placard pressure at such a low ambient. But I would not set them to a corrected STP - 5psig either - , maybe an in between fudge factor, as I don't like to see below 27 or 28psig in a unladen vehicle. - Ken
And when are we going to stop with this Nitrogen nonsense?
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This is my white whale. To get all 4 tires to show the same. Not only the same, but as they heat up to change to the next higher psi at the same time. Futility I know. My brain also tells me the sensors could very well be off and my gauge is more accurate. One more thing to keep me up at nights, that **** left front is .65 psi too high
.My right front reads 1 psig higher starting outThis is my white whale. To get all 4 tires to show the same. Not only the same, but as they heat up to change to the next higher psi at the same time. Futility I know. My brain also tells me the sensors could very well be off and my gauge is more accurate. One more thing to keep me up at nights, that **** left front is .65 psi too high
Can you make me wiser about the temperature BMW includes in their I-drive .
Mayby I can use it to prove my statement about that lower ambiënt temperature can do with lower pressure. But more important at higher ambiënt temperature you need higher pressure. As described in post # 23.
Can do it by PM or on my hotmail.com adres with username jadatis ( combine yourselves, spamm robots cant this way)
Also did research on Nitrogen filling, and came to same conclusion as you did.
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- Nov 29, 2021
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Check all 4 cold or within less than 1 mile for uniformity.
Having the caps off before taking the readings helps immensely.
Having the caps off before taking the readings helps immensely.
^^YUP^^
I walk around the car removing the valve caps. Think of the hood ornament as 12 o'clock. RF tire is #1, RR is #2, LR is #3 and LF is #4.
Take pressures before the Sun hits any of them.
Adjust as needed.
Replace the caps.
Aaaaaaand because so many people can't do this we have to buy TPMS systems. Thanks to every person who won't bend in the middle or is convinced they can't understand things.
The Mazda3 was going on a 800 mile errand last Summer.
36 psi (normal) + 10% for highway driving = 39.6 psi....so I gave it 40.
A friend went on and on about me blowing up tires on the highway.
I wish CapriRacer's post (thanks CR) was in my head at that time.
I walk around the car removing the valve caps. Think of the hood ornament as 12 o'clock. RF tire is #1, RR is #2, LR is #3 and LF is #4.
Take pressures before the Sun hits any of them.
Adjust as needed.
Replace the caps.
Aaaaaaand because so many people can't do this we have to buy TPMS systems. Thanks to every person who won't bend in the middle or is convinced they can't understand things.
The Mazda3 was going on a 800 mile errand last Summer.
36 psi (normal) + 10% for highway driving = 39.6 psi....so I gave it 40.
A friend went on and on about me blowing up tires on the highway.
I wish CapriRacer's post (thanks CR) was in my head at that time.
I got extra set of green caps in Wal Mart. I am all set
I know mine have been set to door placard at cold, not driven on, usually first thing in the AM or later at night after sitting many hours.
I have found that just sitting in the sun brings them up 1-2 psi. but only on the 1-2 where the sun hits. Shady side stays at cold inflation pressure.
I have found that just sitting in the sun brings them up 1-2 psi. but only on the 1-2 where the sun hits. Shady side stays at cold inflation pressure.
I run different pressures in the winter months compared to other times of the year.
Temperature swings in the winter around here are crazy. It can be in the 40's-50's then drop in to the teens for a few days, then go back in to the 30-40's, etc. In the winter I wait until the first 30 degree day, and then set the pressures 2-3psi above the placard. That gives me a 20-30 degree "swing" where the tires will not drop below the recommended pressure and set the TPMS. Then a few months later when the temps start to go back to "normal", I will adjust them to 1-2psi over the recommended pressure since the temperature swings aren't as severe.
We had a cold snap yesterday where it went down to 15 degrees. My tires were at 35-36 (recommended is 35) so the TPMS was perfectly happy. After driving 24 miles to work, they were reading 37-38. Again, pretty normal.
Temperature swings in the winter around here are crazy. It can be in the 40's-50's then drop in to the teens for a few days, then go back in to the 30-40's, etc. In the winter I wait until the first 30 degree day, and then set the pressures 2-3psi above the placard. That gives me a 20-30 degree "swing" where the tires will not drop below the recommended pressure and set the TPMS. Then a few months later when the temps start to go back to "normal", I will adjust them to 1-2psi over the recommended pressure since the temperature swings aren't as severe.
We had a cold snap yesterday where it went down to 15 degrees. My tires were at 35-36 (recommended is 35) so the TPMS was perfectly happy. After driving 24 miles to work, they were reading 37-38. Again, pretty normal.
guy bought 2018 mitsubishi asx, has tpms, but can´t see any numbers... pretty stupid system imho.