Reference temp for recommended tyre pressure
Discussion
Swbimmer said:
so you are basically saying as we go towards winter and temperatures keep dropping (and thus pressure drops), we need to keep topping up the pressure every so often?
Yes, as you say, the pressure drops and therefore won’t be correct.In reality, check them every week or two and you’ll be fine.
As " pigheaded Dutch selfdeclared tyrepressure-specialist" I go for 18 degr C, but 20 drgr C gives that marginal difference that its not worth the discussion, who is right.
Pressure advice cold is given , to give the tyre a warm pressure, so deflection, that wont overheat any part of tyre, when driving the speed constantly, for wich it is calculated.
But warm pressure is verry inacurate to determine, how warm did the tire inside have gotten, an howmuch it already cooled down, between stopping and measuring.
Cold pressure is simply when inside- and outside-tyre temperature is the same.
When ambiënt temp is for instance 37 degrC, cold pressure is higher then at 18 degr C, wich gives lesser tempdifference between rubber and in and outside tyre aire when warm wich gives lesser cooling down of tyre-rubber.
But then lesser deflection by higher pressure, wich gives lesser heatproduction,.
For 10 degrC the other way around.
So within a certain range of ambiënt temperature, cooling down and heating up of tyre is in ballance, so no part of tyre reaches the critical temperature, at wich it hardens and beginning crackes are made.
My estimation is up to 35 degr C .
Then calculate back the pressure to 18 degr C , and compare that to the advice.
When 10 degrC you then dont need to highen up the pressure to advice for safety, but may do it for roadhandling.
At 37 degrC , never bleed air to the 18 degr advice pressure, and if it then gives discomfort , so be it, the tyre needs the lesser deflection to give the lesser heatproduction.
Here a list for psi, the degr C at the back, and F at front, can also give it in Bar/kPa.
Pressure advice cold is given , to give the tyre a warm pressure, so deflection, that wont overheat any part of tyre, when driving the speed constantly, for wich it is calculated.
But warm pressure is verry inacurate to determine, how warm did the tire inside have gotten, an howmuch it already cooled down, between stopping and measuring.
Cold pressure is simply when inside- and outside-tyre temperature is the same.
When ambiënt temp is for instance 37 degrC, cold pressure is higher then at 18 degr C, wich gives lesser tempdifference between rubber and in and outside tyre aire when warm wich gives lesser cooling down of tyre-rubber.
But then lesser deflection by higher pressure, wich gives lesser heatproduction,.
For 10 degrC the other way around.
So within a certain range of ambiënt temperature, cooling down and heating up of tyre is in ballance, so no part of tyre reaches the critical temperature, at wich it hardens and beginning crackes are made.
My estimation is up to 35 degr C .
Then calculate back the pressure to 18 degr C , and compare that to the advice.
When 10 degrC you then dont need to highen up the pressure to advice for safety, but may do it for roadhandling.
At 37 degrC , never bleed air to the 18 degr advice pressure, and if it then gives discomfort , so be it, the tyre needs the lesser deflection to give the lesser heatproduction.
Here a list for psi, the degr C at the back, and F at front, can also give it in Bar/kPa.
Edited by Jadatis on Tuesday 1st September 21:58
Edited by Jadatis on Tuesday 1st September 22:06
Resurrecting this old thread about "cold" tyre pressure and whether to adjust for the ambient in which the pressures are measured. I would love to find something definitive on this.
20 years ago technical liaison at Michelin told me that cold pressure was (then) measured at 17° C and it would change buy 0.01 bar for each 1°C.
eg. If a tyre was 2.2 bar at 17° then at at 37° it would be at 2.4 bar. (0.01 x 20)
Similarly if was measured at 7° then that same tyre would be at 2.1 bar.
Ideally the tyres should be adjusted to the correct cold pressure in a garage at 17° and then they will be right, if you have to set them in ambient temperature that is different the cold pressure that you use should be adjusted for this.
Since then the standard temperature for "cold" tyres has been changed to 20°
Some time later another technical guy, this time at Pirelli, said that this was wrong. he said the cold temperature should be at the current ambient, and you should adjust your tyre pressures depending upon the weather. So if my tyres were correct (say 2.2) when inflated in a warm garage, but then parked outside in the cold at 0° I would have to increase the pressures by 0.2 bar to bring them back up. I have read other advice that says the same thing, adjust them for the ambient you will use them in.
Now my current car (Porsche) has TPMS system, which seems accurate. The pressure displayed concur with my gauges and the calibrated gauge at the Porsche Centre.
But the on board computer has a function to tell you how much to adjust the tyre pressures, and the manual is clear that it is this display that should be observed, not the pressures displayed whilst driving. It states that the "Fill info" is adjusted for temperature.
Currently my tyres are at 2.2 bar, the correct cold pressure which the manual lists as being at 20°C. But it is cold outside - not much above 0 currently.
The fill info on the TPMS display says that my tyres needed to be reduced by 0.2 bar.
I guess that Porsche agree with what the Michelin guy said all those years ago.
20 years ago technical liaison at Michelin told me that cold pressure was (then) measured at 17° C and it would change buy 0.01 bar for each 1°C.
eg. If a tyre was 2.2 bar at 17° then at at 37° it would be at 2.4 bar. (0.01 x 20)
Similarly if was measured at 7° then that same tyre would be at 2.1 bar.
Ideally the tyres should be adjusted to the correct cold pressure in a garage at 17° and then they will be right, if you have to set them in ambient temperature that is different the cold pressure that you use should be adjusted for this.
Since then the standard temperature for "cold" tyres has been changed to 20°
Some time later another technical guy, this time at Pirelli, said that this was wrong. he said the cold temperature should be at the current ambient, and you should adjust your tyre pressures depending upon the weather. So if my tyres were correct (say 2.2) when inflated in a warm garage, but then parked outside in the cold at 0° I would have to increase the pressures by 0.2 bar to bring them back up. I have read other advice that says the same thing, adjust them for the ambient you will use them in.
Now my current car (Porsche) has TPMS system, which seems accurate. The pressure displayed concur with my gauges and the calibrated gauge at the Porsche Centre.
But the on board computer has a function to tell you how much to adjust the tyre pressures, and the manual is clear that it is this display that should be observed, not the pressures displayed whilst driving. It states that the "Fill info" is adjusted for temperature.
Currently my tyres are at 2.2 bar, the correct cold pressure which the manual lists as being at 20°C. But it is cold outside - not much above 0 currently.
The fill info on the TPMS display says that my tyres needed to be reduced by 0.2 bar.
I guess that Porsche agree with what the Michelin guy said all those years ago.
Edited by Wollemi on Tuesday 7th February 13:10
I found a pdf from RIMEX, for earthmovers, and they use 20 degrC is 68 degrF. They call it indexed temperature.
But another belgian firm for trucktires uses 15 degrC
18vdegrC / I also saw mentioned.
Now busy with making a spreadsheet in wich begin temperature and pressure given first.
Then change temperature, and see how pressure changes in case of absolutely dry air, and if water enaugh in tire.
Last part is to give changed pressure, and it gives new temperature if dry, not yet for wet, but figuring it out.
If you want to try, mail me at my hotmail.com adress with username jadatis, and I will send it to you.
Like this to prefent spamm, so combine yourselfes.
But another belgian firm for trucktires uses 15 degrC
18vdegrC / I also saw mentioned.
Now busy with making a spreadsheet in wich begin temperature and pressure given first.
Then change temperature, and see how pressure changes in case of absolutely dry air, and if water enaugh in tire.
Last part is to give changed pressure, and it gives new temperature if dry, not yet for wet, but figuring it out.
If you want to try, mail me at my hotmail.com adress with username jadatis, and I will send it to you.
Like this to prefent spamm, so combine yourselfes.
I would like a copy of the pressure part of Porche manuall, so I can read about the reference temperature.
But already completed my spreadsheet calculator for wet and dry gascompound.
For who is interested, mail me at my hotmail. com adress with username jadatis, and I will send it back in return.
But already completed my spreadsheet calculator for wet and dry gascompound.
For who is interested, mail me at my hotmail. com adress with username jadatis, and I will send it back in return.
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