Tyre pressures, one for the boffins
Discussion
Reading this months Sprint (TVROC magazine) an article about tyres.
"Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
I am struggling with this, perhaps too much Christmas pud. Assuming the tyres are at ambient temperature, why would a change in temperature alter the pressure?
Have vague recollections of Boyd s Laws from many years ago not sure that this is relevant where the temp inside and outside the vessel (the Tyre) is the same.
If we were to be pedantic I think that perhaps a tyre pressure set at sea level would need to be be reduced to read the same at the top of a high mountain pass due to the reduced atmospheric pressure.
What do you all think, am I wrong ( not unusual) or have Sprint got it wrong?
"Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
I am struggling with this, perhaps too much Christmas pud. Assuming the tyres are at ambient temperature, why would a change in temperature alter the pressure?
Have vague recollections of Boyd s Laws from many years ago not sure that this is relevant where the temp inside and outside the vessel (the Tyre) is the same.
If we were to be pedantic I think that perhaps a tyre pressure set at sea level would need to be be reduced to read the same at the top of a high mountain pass due to the reduced atmospheric pressure.
What do you all think, am I wrong ( not unusual) or have Sprint got it wrong?
Go to your freezer. Open the door and let some warm air in, then close the door again.
The warm air will cool down and the pressure in the freezer will lower slightly, enough to make opening the door a bit more difficult°
Same thing happens with your car tyres.
°assuming there aren't any air leaks and there is enough room in the freezer for air to get to.
The warm air will cool down and the pressure in the freezer will lower slightly, enough to make opening the door a bit more difficult°
Same thing happens with your car tyres.
°assuming there aren't any air leaks and there is enough room in the freezer for air to get to.
Of course the pressure changes with ambient temperature. Easily tested empirically.
If you want the quick home test, take a jam jar, leave it in the freezer for half an hour (cold winter night in North Yorkshire) and take it out and put the lid on quickly before it warms up. Now put it in a basin of warm water for five minutes (representing hot day in some soft Southern climate). Now take the lid off and observe the puff of air come out as a result of the pressure having built up.
(Don't use boiling water as the glass may shatter)
Why? Check out Boyle's Law. (not Boyd's Law)
https://en.wikipedia.org/wiki/Boyle%27s_law
This part:
"If we were to be pedantic I think that perhaps a tyre pressure set at sea level would need to be be reduced to read the same at the top of a high mountain pass due to the reduced atmospheric pressure."
... Yes, you're right in principle though in practice it's not a very significant effect. Though it's not really "needed" as you would be unwise to go over 10,000 feet without oxygen for long, and that's only about 4 or 5 psi difference from sea level.
Also, at 10,000 feet it is would normally be about 20 degrees C colder than at sea level in the same general location, so that would reduce the difference (assuming cold tyres).
If you want the quick home test, take a jam jar, leave it in the freezer for half an hour (cold winter night in North Yorkshire) and take it out and put the lid on quickly before it warms up. Now put it in a basin of warm water for five minutes (representing hot day in some soft Southern climate). Now take the lid off and observe the puff of air come out as a result of the pressure having built up.
(Don't use boiling water as the glass may shatter)
Why? Check out Boyle's Law. (not Boyd's Law)
https://en.wikipedia.org/wiki/Boyle%27s_law
This part:
"If we were to be pedantic I think that perhaps a tyre pressure set at sea level would need to be be reduced to read the same at the top of a high mountain pass due to the reduced atmospheric pressure."
... Yes, you're right in principle though in practice it's not a very significant effect. Though it's not really "needed" as you would be unwise to go over 10,000 feet without oxygen for long, and that's only about 4 or 5 psi difference from sea level.
Also, at 10,000 feet it is would normally be about 20 degrees C colder than at sea level in the same general location, so that would reduce the difference (assuming cold tyres).
Edited by Lowtimer on Thursday 26th December 21:46
MethylatedSpirit said:
Go to your freezer. Open the door and let some warm air in, then close the door again.
The warm air will cool down and the pressure in the freezer will lower slightly, enough to make opening the door a bit more difficult°
You are a clever lot, I always thought that was due to a magnetic strip in the door seal!!!!!! Oh dear, I appear to have had an excess of Christmas cheer, will look at your replies again in the morning when I can understand it all The warm air will cool down and the pressure in the freezer will lower slightly, enough to make opening the door a bit more difficult°
The air outside the tyre also gets colder, and therefore contracts, but its pressure is mainly set by the total weight of the atmosphere above it pushing down and so doesn't change much. The air in the tyre is a fixed amount (mass) of air in a fixed volume, and so PV=nRT applies with constant V, n and R and pressure is proportional to temperature (in degrees Kelvin)
Lowtimer said:
...Though it's not really "needed" as you would be unwise to go over 10,000 feet without oxygen for long...
Err... 10,000ft is only about 3000m, nowhere near high enough altitude to need supplemental oxygen. Double that and most people will take a while to acclimatise, above about 7500m (25,000ft) most mountaineers will be using supplemental oxygen.In one sense you're right though, you would be unwise to go without oxygen for long at any altitude
Science aside (and i am as literate as most above) if one does one's weekly checks one should be fine. Unless there is freak weather and a change of 10s of degrees in a week.
Let's consider tvr owners perhaps leave their cars a few weeks undriven at a time, and at this timr of year physics may catch out the unwary.
Let's consider tvr owners perhaps leave their cars a few weeks undriven at a time, and at this timr of year physics may catch out the unwary.
Science aside (and i am as literate as most above) if one does one's weekly checks one should be fine. Unless there is freak weather and a change of 10s of degrees in a week.
Let's consider tvr owners perhaps leave their cars a few weeks undriven at a time, and at this timr of year physics may catch out the unwary.
Let's consider tvr owners perhaps leave their cars a few weeks undriven at a time, and at this timr of year physics may catch out the unwary.
I park my F150 for 4 days at a time then bounce along the road for the first few miles because the air in the tires has frozen leaving a flatter spot at the bottom of the rim until the tire warms up.Plus 40c to minus 40c throughout our seasons and that can really screw with vehicles , helps if you can drive properly though .
TVR's
,don't see many .
TVR's
,don't see many .TVR keith said:
Reading this months Sprint (TVROC magazine) an article about tyres.
"Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
Bit slack not bothering to translate from degF to degC. (ETA: not the OP, but the author)"Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
27 degC to -29degC??? Get that a lot in the UK...
Of course, you could go from the upper end of that to ~freezing, but then (assuming their maths is correct) you're looking at a ~5 psi change. Daresay most of the motoring population wouldn't notice if their tyres were out by that.
Edited by LooneyTunes on Friday 27th December 07:58
TVR keith said:
Reading this months Sprint (TVROC magazine) an article about tyres.
"Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
Apart from him not living in the UK, and just c'n'p-ing some stateside rubbish, anybody who'd leave tyres for six months and not even bother checking the pressures is very much the kind of numpty to think they sound clueful by tautologically repeating the units in "lbs PSI"."Tyre pressures change with the outside temperature; tyre pressure decrease by approximately 1 1bs per square inch for every 10 degrees drop in the outside temperature. For example if your tyres were last checked in the summer when the temperature was 80 degrees and it is now winter time and the temperature has dropped to -20 degrees your tyres may well be under inflated by as much as 101bs PSI which would be very dangerous"
fttm said:
I park my F150 for 4 days at a time then bounce along the road for the first few miles because the air in the tires has frozen leaving a flatter spot at the bottom of the rim until the tire warms up.Plus 40c to minus 40c throughout our seasons and that can really screw with vehicles , helps if you can drive properly though .
TVR's,don't see many .
The air has not frozen, even at -40c.TVR's
,don't see many .fttm said:
I park my F150 for 4 days at a time then bounce along the road for the first few miles because the air in the tires has frozen leaving a flatter spot at the bottom of the rim until the tire warms up.Plus 40c to minus 40c throughout our seasons and that can really screw with vehicles , helps if you can drive properly though .
TVR's,don't see many .
ROFLMAOTVR's
,don't see many .GravelBen said:
Err... 10,000ft is only about 3000m, nowhere near high enough altitude to need supplemental oxygen. Double that and most people will take a while to acclimatise, above about 7500m (25,000ft) most mountaineers will be using supplemental oxygen.
In one sense you're right though, you would be unwise to go without oxygen for long at any altitude
The RAF used to recommend the use of oxygen from 10,000 feet in non-pressurised aircraft IIRC. Where's Eric or Ginetta Girl?In one sense you're right though, you would be unwise to go without oxygen for long at any altitude
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