Setting tyre pressures in cold weather
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Hi,
I checked my tyre pressures yesterday morning with my trusty hand gauge, and they were quite low (24-26Psi). I assume that this was due to low ambient temperatures overnight.
My question is this - is there a 'standard' temperature for the tyre pressues on the door sticker?. I know that tyre pressures are measured when cold, but I imagine that boyles law would mean that the tyres will be over inflated when they are at working temperature if filled to the recommended pressures when very cold.
My engineering ruler is calibrated at 20c - is there a similar datum for the tyre pressures?.
Rgds,
Alex
I checked my tyre pressures yesterday morning with my trusty hand gauge, and they were quite low (24-26Psi). I assume that this was due to low ambient temperatures overnight.
My question is this - is there a 'standard' temperature for the tyre pressues on the door sticker?. I know that tyre pressures are measured when cold, but I imagine that boyles law would mean that the tyres will be over inflated when they are at working temperature if filled to the recommended pressures when very cold.
My engineering ruler is calibrated at 20c - is there a similar datum for the tyre pressures?.
Rgds,
Alex
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Alex
I was wondering exactly the same thing myself this morning. I'll be setting my tyre pressures tonight for Donington (spectator, white knuckle rider hopefully!) and following Rally GB and I'm a bit concerned about setting them at low temperature and then having them over-inflated when up to working temperature.
Someone out there must know the answer....
Regards
Nigel A
PS Has anyone else found petrol station tyre gauges to be inaccurate? My local Texaco showed a pressure of 32 lb/sqin when my hand held gauge showed 26!
I was wondering exactly the same thing myself this morning. I'll be setting my tyre pressures tonight for Donington (spectator, white knuckle rider hopefully!) and following Rally GB and I'm a bit concerned about setting them at low temperature and then having them over-inflated when up to working temperature.
Someone out there must know the answer....
Regards
Nigel A
PS Has anyone else found petrol station tyre gauges to be inaccurate? My local Texaco showed a pressure of 32 lb/sqin when my hand held gauge showed 26!
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Nigel,
I think the question should be 'has anyone found an accurate forecourt tyre pressure gauge'. The design everyone uses in the UK is complete rubbish anyway - In French Autoroute service stations, the hose is secured onto the valve by a spring loaded clip, and you have a nice big accurate gauge with buttons to increase or decrease pressure. No squatting down on the ground trying to read a gauge which is usually filled with condensation in the dark, and is woefully inaccurate at the best of times..
And to add insult to injury, most garages now seem to charge for the privilege!.
Rgds,
Alex
I think the question should be 'has anyone found an accurate forecourt tyre pressure gauge'. The design everyone uses in the UK is complete rubbish anyway - In French Autoroute service stations, the hose is secured onto the valve by a spring loaded clip, and you have a nice big accurate gauge with buttons to increase or decrease pressure. No squatting down on the ground trying to read a gauge which is usually filled with condensation in the dark, and is woefully inaccurate at the best of times..
And to add insult to injury, most garages now seem to charge for the privilege!.
Rgds,
Alex
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It is (or should be!) well known that garage pressure gauages are hopelessly inaccurate, unless you are lucky enough to get there just as it has been calibrated! Just think of all the moisture,diesel, kickings these guages get?
Get yourself a pencil guage from Halfors and keep it in the glovebox. These have been shown to be the cheapest, most precise/accurate guages out there for the price. For a couple of quid get one and renew it once a year.
Dave
Get yourself a pencil guage from Halfors and keep it in the glovebox. These have been shown to be the cheapest, most precise/accurate guages out there for the price. For a couple of quid get one and renew it once a year.
Dave
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Hi Dave,
Halfords do a nice rotary dial gauge for around a tenner. It is graduated in 0.5psi markings and is BS approved, so it will be reasonably accurate and is easier to read than the pencil type. I usually over inflate the tyres slightly, and reduce the pressure with the gauge until it is spot on.
Cheers,
Alex
Halfords do a nice rotary dial gauge for around a tenner. It is graduated in 0.5psi markings and is BS approved, so it will be reasonably accurate and is easier to read than the pencil type. I usually over inflate the tyres slightly, and reduce the pressure with the gauge until it is spot on.
Cheers,
Alex
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Alex
The tyre pressures should be set to their "cold" value at whatever the ambient temperature is.
When the tyres heat up they do so by a given increment not to an absolute value, and so although the pressure increase will not be exactly linear (because Boyle's law uses degrees Kelvin; 273k = 0 degC) it is near enough.
Put another way - the tyre pressure is there to support the car over a given contact patch area. The weight of the car dosn't change with outside temperature, so neither should the tyre pressures no matter if the day is hot or cold.
Alternatively move to Aberdeen where it's miserable and cold all the time and you can leave your tyres alone all year !!
Russ
The tyre pressures should be set to their "cold" value at whatever the ambient temperature is.
When the tyres heat up they do so by a given increment not to an absolute value, and so although the pressure increase will not be exactly linear (because Boyle's law uses degrees Kelvin; 273k = 0 degC) it is near enough.
Put another way - the tyre pressure is there to support the car over a given contact patch area. The weight of the car dosn't change with outside temperature, so neither should the tyre pressures no matter if the day is hot or cold.
Alternatively move to Aberdeen where it's miserable and cold all the time and you can leave your tyres alone all year !!
Russ
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Thanks Russ - that is what I had suspected.
I should check my tyres again to see what pressure they are as it has been **slightly** warmer of late. It was near freezing when I last set the pressure.
Rgds,
Alex
I should check my tyres again to see what pressure they are as it has been **slightly** warmer of late. It was near freezing when I last set the pressure.
Rgds,
Alex
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russell, stop talking *****.
If the weather is cold the pressure will drop as the gas in the tyre is colder.
Why do you think race cars have their tyre presures checked after every run. Because tyre temperature and external track temp have an effect on the temp and pressure of the gas.
The main reason that tyre presures change with temperature is due to the expansion of the water molecules in the air in the tyre.
If you want to minimise this effect you would use a pure gas to inflate the tyres and not a water vapour filled air charge.
set your tyre pressures on a warm day, then check them on a cold day, they will be different.
If the weather is cold the pressure will drop as the gas in the tyre is colder.
Why do you think race cars have their tyre presures checked after every run. Because tyre temperature and external track temp have an effect on the temp and pressure of the gas.
The main reason that tyre presures change with temperature is due to the expansion of the water molecules in the air in the tyre.
If you want to minimise this effect you would use a pure gas to inflate the tyres and not a water vapour filled air charge.
set your tyre pressures on a warm day, then check them on a cold day, they will be different.
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I second (most) of that John!
Russell probably doesn't get to see as much temperature difference as more southerly based individuals. He probably doesn't get to notice the lovely increase in GO when the weather gets cooler either!
Moray
(Got to go now, it's cold and dark outside and Ive got to go home!
)
Russell probably doesn't get to see as much temperature difference as more southerly based individuals. He probably doesn't get to notice the lovely increase in GO when the weather gets cooler either!
Moray
(Got to go now, it's cold and dark outside and Ive got to go home!
)
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John and Moray
You have totally misread and misunderstood what I said !!!!
Of course they deflate when the temperature drops.
If you'd read my second paragraph you'll see that I am quite conversant with Boyle's law (bloody well hope so - I design oil and gas wells in the North Sea !)
I said that the tyre pressures should be set to whatever value you are using (say 33/28) whatever the AMBIENT temperature is.
So when you get up in the morning to check your pressures and it's 0 degC, you set them at 33/28.
When you get up the next morning and it's 20 degC, the tyre pressures will have increased, and so you need to bleed them back to 33/28.
What you don't do is set them at 33/28 at a "standard" temperature and then leave them to fluctuate with ambient.
Russ
You have totally misread and misunderstood what I said !!!!
Of course they deflate when the temperature drops.
If you'd read my second paragraph you'll see that I am quite conversant with Boyle's law (bloody well hope so - I design oil and gas wells in the North Sea !)
I said that the tyre pressures should be set to whatever value you are using (say 33/28) whatever the AMBIENT temperature is.
So when you get up in the morning to check your pressures and it's 0 degC, you set them at 33/28.
When you get up the next morning and it's 20 degC, the tyre pressures will have increased, and so you need to bleed them back to 33/28.
What you don't do is set them at 33/28 at a "standard" temperature and then leave them to fluctuate with ambient.
Russ
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