What temp. should tyre be when you take pressure reading?

[ejohnh]

It was about -1C in my garage today when I checked tyre pressures. 25psi front 29psi back. Is that normal(re Charles' Law) for a dead cold tyre?

JohnH

[timwilky]

The combined gas laws would apply and as the volume of an inflated tyre is effectively constant then pressure is directly proportional to temperature.

So this would result in a perfect non leaking tyre seeing about a 2-3 lb loss as a result of a change in ambient temperature form a nice 16 to a chilly -1.


So you would appear to have lost a tad more. Add about 5lb only as once the tyre gets up to full working temperature you may find it otherwise over inflated.

[ejohnh]

The combined gas laws would apply and as the volume of an inflated tyre is effectively constant then pressure is directly proportional to temperature.

So this would result in a perfect non leaking tyre seeing about a 2-3 lb loss as a result of a change in ambient temperature form a nice 16 to a chilly -1.


So you would appear to have lost a tad more. Add about 5lb only as once the tyre gets up to full working temperature you may find it otherwise over inflated.

Thanks Prof. :shock:

[RandyO]

recommended pressures are for cold tires

[wheelnut]

recommended pressures are for cold tires

But what is a cold tyre?

A cold tyre in Tangiers might be 20degree C and in Glesga a cold tyre could be -5'c

[timwilky]

Yes, tyre pressure must always be checked on a cold tyre.

I was simply making the point that the pressure will change as a result of a major change in ambient temperature. Checking the pressure first thing in the morning during a frost is perhaps not a good time to do it if the temperature during the day will rise by about 8 degrees celcius.

As I said the combined gas law applies. there pv/t =c and assuming there is no change in volume then


We need to use absolute (Kelvin) temperature
P1/t1 = p2/t2. So assuming a starting -1 Celsius and an initial pressure of 36 psi.
p2= (36/271.15) * 279.15)

Then by the ambient temperature rising by 8 degrees during the day. a tyre having been inflated to 36 psi would become 37psi.

I know it is not alot. of change. However if the tyre is inflated in the depth of winter without any loss it may become seriously over inflated in the height of summer.

[ejohnh]

Yes, tyre pressure must always be checked on a cold tyre.

I was simply making the point that the pressure will change as a result of a major change in ambient temperature. Checking the pressure first thing in the morning during a frost is perhaps not a good time to do it if the temperature during the day will rise by about 8 degrees celcius.

As I said the combined gas law applies. there pv/t =c and assuming there is no change in volume then


We need to use absolute (Kelvin) temperature
P1/t1 = p2/t2. So assuming a starting -1 Celsius and an initial pressure of 36 psi.
p2= (36/271.15) * 279.15)

Then by the ambient temperature rising by 8 degrees during the day. a tyre having been inflated to 36 psi would become 37psi.

I know it is not alot. of change. However if the tyre is inflated in the depth of winter without any loss it may become seriously over inflated in the height of summer.

O dear, enough of the respect.

During a ride a tyre will achieve a temperature that is probably independent of the ambient. When Suzuki or mr rubber company give a recommended tyre pressure it is worked out on what the warmed up tyre pressure is likely to be.

What is the temperature at which the Suzuki given recommended pressures apply? Someone said 'cold'. What exactly is 'cold'?

Since pressure for a gas in a fixed volume is directly proportional to temperature it is surely obvious that for a given volume of air, a tyre will read a higher pressure at 16C than at 2C.

Does anybody know what the 'standard' temperature is? No more blinding(no information) science please! :o)

Happy new Year

JohnH

[Cam_73]

Tyre pressures are cold check.

As the temp change takes place over a very long period (in math/ engineering terms)

Assume the tyre volume is constant.

in short. the -1 deg. c doesn't really matter.

Cheers

[kwak zzr]

i really must pay more attention to my tyres :roll: if there pumped up around 35ish then that ok :oops:

[ejohnh]

Tyre pressures are cold check.

As the temp change takes place over a very long period (in math/ engineering terms)

Assume the tyre volume is constant.

in short. the -1 deg. c doesn't really matter.

Cheers

I had to check out the combined gas law on the net for this:
Assuming that the advised pressures are give for a 'cool' tyre (ie at 16C) then the pressure at -1C should be approximately 2 lbs less.

ie combined gas law is P1.V1/T1 = P2.V2/T2. Volume is constant so P/T is constant. T is kelvin so P2 = P1.T2/T1. So if front tyre pressure at 16C is 30psi then front tyre pressure at -1C = 30x272/289 = 28psi. Probably doesn't matter a toss.

John

what a way to spend Christmas!

[RandyO]

recommended pressures are for cold tires

But what is a cold tyre?

A cold tyre in Tangiers might be 20degree C and in Glesga a cold tyre could be -5'c



cold tire temp is the temp on tires that haven't been warmed up on any given day by riding on them

don't worry about ambient temperature

when tires are warmed up, they increase pressure by 4-6psi

[ejohnh]

recommended pressures are for cold tires

But what is a cold tyre?

A cold tyre in Tangiers might be 20degree C and in Glesga a cold tyre could be -5'c



cold tire temp is the temp on tires that haven't been warmed up on any given day by riding on them

don't worry about ambient temperature

when tires are warmed up, they increase pressure by 4-6psi

You cannot ignore ambient temperature because tyre pressure varies with it. A 17C difference in ambient temperature gives a 2psi (approx) diff in pre-warmup pressure. Probably splitting hairs if you are content to be 2psi out on your running pressure.

Happy New Year
John

[Alpinestarhero]

cold being around 15-20 degrees. Thats cold enough from optimum operating temp of 60-70 degrees!

Matt

[ejohnh]

cold being around 15-20 degrees. Thats cold enough from optimum operating temp of 60-70 degrees!

Matt

you are studying chemistry?

I studied applied heat. 15-20C approximates to 60-70F, the rest is what? Are you saying that tyres get up to 70C? If so I am amazed.

JohnH

[RandyO]

recommended pressures are for cold tires

But what is a cold tyre?

A cold tyre in Tangiers might be 20degree C and in Glesga a cold tyre could be -5'c



cold tire temp is the temp on tires that haven't been warmed up on any given day by riding on them

don't worry about ambient temperature

when tires are warmed up, they increase pressure by 4-6psi

You cannot ignore ambient temperature because tyre pressure varies with it. A 17C difference in ambient temperature gives a 2psi (approx) diff in pre-warmup pressure. Probably splitting hairs if you are content to be 2psi out on your running pressure.

Happy New Year
John

yes, IGNORE ambient temperture

what ever temperature it is when you start to ride, check your pressure before you ride, if the pressure doesn't meet recommended cold pressure, raise or lower it accordingly, regardless of temperature

[ejohnh]

Does anyone know what temp a tyre achieves when it is warmed up? Is it fairly constant?

[RandyO]

Does anyone know what temp a tyre achieves when it is warmed up? Is it fairly constant?


40°F-60°F above ambient temperature,