tyre pressures, what causes the loss?

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tyre pressures, what causes the loss?

Postby DoubleSpeeded » Sat Sep 21, 2013 2:48 pm

HI guys

im curious... not that its a big problem... as tyre pressure should be checked and re adjusted/pumped prior to every ride.

23mm Tyres, i noticed loses more air pressure than larger tyres im assuming due to less air volume

say 110psi... few days it can go down to about 95psi.


but where is it lost?... the Schrader/presta valves?...
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Re: tyre pressures, what causes the loss?

Postby Tornado » Sat Sep 21, 2013 3:07 pm

I'm guessing with higher pressures it is easier for it to bleed through the rubber.
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Re: tyre pressures, what causes the loss?

Postby darkelf921 » Sat Sep 21, 2013 3:11 pm

The air simply escapes through the tube (slowly). The air molecules are simply smaller than the rubber molecules. This can be seen by filling your tube with a CO2 canister. Those molecules are even smaller so the tyre goes flat, quicker. You notice it more on the 23s as there is greater pressure. Just think of a balloon. It holds the air when blown up but eventually the balloon will lose all of the air.

This is normal. Part of your safety check before riding should be to check the tyre pressure. I simply push my thumb into the tyre to check it. You get used to what is right.
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Re: tyre pressures, what causes the loss?

Postby DoubleSpeeded » Sat Sep 21, 2013 3:25 pm

darkelf921 wrote:The air simply escapes through the tube (slowly). The air molecules are simply smaller than the rubber molecules. This can be seen by filling your tube with a CO2 canister. Those molecules are even smaller so the tyre goes flat, quicker. You notice it more on the 23s as there is greater pressure. Just think of a balloon. It holds the air when blown up but eventually the balloon will lose all of the air.

This is normal. Part of your safety check before riding should be to check the tyre pressure. I simply push my thumb into the tyre to check it. You get used to what is right.



fairdinkum

thats interesting..

goes through the microscopic pores of the rubber...

learn something new every day.


but then again what about tubeless?
a car tyre holds pressure very well, when its clinched with a steel or alloy rim?
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Re: tyre pressures, what causes the loss?

Postby Mulger bill » Sat Sep 21, 2013 4:37 pm

Car tyres are built from much thicker rubber would be my guess.
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Re: tyre pressures, what causes the loss?

Postby visrealm » Sat Sep 21, 2013 5:11 pm

It's a combination of pressure and low volume. If a bigger tyre lost the same volume of air, it wouldn't affect the pressure nearly as much. Think about a car tyre losing the entire volume of a bike tyre, it would make two tenths of bugger all difference to the pressure.

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Re: tyre pressures, what causes the loss?

Postby foo on patrol » Sat Sep 21, 2013 7:23 pm

darkelf921 wrote:The air simply escapes through the tube (slowly). The air molecules are simply smaller than the rubber molecules. This can be seen by filling your tube with a CO2 canister. Those molecules are even smaller so the tyre goes flat, quicker. You notice it more on the 23s as there is greater pressure. Just think of a balloon. It holds the air when blown up but eventually the balloon will lose all of the air.

This is normal. Part of your safety check before riding should be to check the tyre pressure. I simply push my thumb into the tyre to check it. You get used to what is right.


The strips/tubs of 30yr ago would lose up to 30psi in two days. It all boils down to porous rubber and seal of valve stem. :wink:

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Re: tyre pressures, what causes the loss?

Postby bychosis » Sat Sep 21, 2013 8:37 pm

I thought it was the gremlins that come out at night and steal single socks and pens, if you haven't got any pens or pairs of socks they let a bit of air out of your tyres.
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Re: tyre pressures, what causes the loss?

Postby BianchiCam » Sat Sep 21, 2013 11:42 pm

^ Well buggaar me, I never..
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Re: tyre pressures, what causes the loss?

Postby DavidI » Tue Sep 24, 2013 11:02 am

bychosis wrote:I thought it was the gremlins that come out at night and steal single socks and pens, if you haven't got any pens or pairs of socks they let a bit of air out of your tyres.

Maybe it's the Underpants Gnomes?
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Re: tyre pressures, what causes the loss?

Postby il padrone » Tue Sep 24, 2013 11:27 am

DoubleSpeeded wrote:but then again what about tubeless?
a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

I believe that tubeless tyres have a different treatment to the inner surface to reduce seepage. Added to this bicycle tubeless tyres are used with a sealant compound inside them.

Motor vehicle tyres are a much thicker rubber construction, with a very tight clincher seal on the rim. They also generally run at much lower pressures than a bike tyre. Lower pressure = lower air loss.
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Re: tyre pressures, what causes the loss?

Postby HappyHumber » Tue Sep 24, 2013 12:34 pm

DavidI wrote:
bychosis wrote:I thought it was the gremlins that come out at night and steal single socks and pens, if you haven't got any pens or pairs of socks they let a bit of air out of your tyres.
Maybe it's the Underpants Gnomes?

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Re: tyre pressures, what causes the loss?

Postby Hamster » Tue Sep 24, 2013 8:32 pm

darkelf921 wrote:The air simply escapes through the tube (slowly). The air molecules are simply smaller than the rubber molecules. This can be seen by filling your tube with a CO2 canister. Those molecules are even smaller so the tyre goes flat, quicker.


A CO2 molecule is considerably larger than either O2 or N2 which are the major constituents of air. A tyre inflated with CO2 loses pressure because CO2 is actually soluble in butyl rubber (the most common material used for tubes) and is thus not constrained to normal permeation loss.
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Re: tyre pressures, what causes the loss?

Postby DoubleSpeeded » Tue Sep 24, 2013 8:46 pm

Hamster wrote:
darkelf921 wrote:The air simply escapes through the tube (slowly). The air molecules are simply smaller than the rubber molecules. This can be seen by filling your tube with a CO2 canister. Those molecules are even smaller so the tyre goes flat, quicker.


A CO2 molecule is considerably larger than either O2 or N2 which are the major constituents of air. A tyre inflated with CO2 loses pressure because CO2 is actually soluble in butyl rubber (the most common material used for tubes) and is thus not constrained to normal permeation loss.


What about Nitrogen filled tyres like The Nissan R35 GT-R?

il padrone wrote:
DoubleSpeeded wrote:but then again what about tubeless?
a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

I believe that tubeless tyres have a different treatment to the inner surface to reduce seepage. Added to this bicycle tubeless tyres are used with a sealant compound inside them.

Motor vehicle tyres are a much thicker rubber construction, with a very tight clincher seal on the rim. They also generally run at much lower pressures than a bike tyre. Lower pressure = lower air loss.


make sense..

HappyHumber wrote:
DavidI wrote:
bychosis wrote:I thought it was the gremlins that come out at night and steal single socks and pens, if you haven't got any pens or pairs of socks they let a bit of air out of your tyres.
Maybe it's the Underpants Gnomes?

God forbid they should ever cross polinate with the Puncture Fairy.


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Re: tyre pressures, what causes the loss?

Postby bychosis » Tue Sep 24, 2013 9:20 pm

It appears I have upset the puncture fairy, flat on my second commute in about 3 weeks. Pressure was ok when I left, then ...
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Re: tyre pressures, what causes the loss?

Postby Hamster » Wed Sep 25, 2013 1:38 pm

As stated before bicycle types filled with CO2 lose pressure because the CO2 dissolves into the butyl rubber rather than simply passing through the rubber.

As regards N2 there is really little difference from using plain old air which is 80% N2. N2 is used in aircraft tyres and race cars because it guarantees that the inflation gas will be free of water vapour. Using a poorly maintained compressor may result in an excessive amount of water vapour being included with the inflation gas. When cold the water will condense but when hot it will become a gas with the result that tyre pressures will greatly increase. With tyres already operating near their design tolerances such as with aircraft this is something to be avoided as blown tyres may result.

As regards ordinary passenger vehicles using N2 is largely hype and a means of charging money for an otherwise free service. The only claimed advantages that MAY have merit are the guarantee that water vapour is excluded and that because the inflation gas does not contain the 20% O2 of air that oxidation of the rim and of the inside of the tyre will be reduced. However, the outside of the tyre is exposed to the air plus normal wear so protecting the inside seems fairly pointless. As regards oxidation of the rim, again the outside of the rim is exposed to the air so again is probably pointless.

Whilst I am not convinced that using N2 in an ordinary car travelling at legal speeds is of any benefit there may be some advantage so if recommended by the manufacturer it would be wise to continue using N2 realizing that it’s probably unnecessary.
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Re: tyre pressures, what causes the loss?

Postby casual_cyclist » Wed Sep 25, 2013 1:41 pm

DoubleSpeeded wrote:a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

Mine don't :evil: I have to check them every couple of months and most of the time they have gone down a little.
I don't check my bike tyres enough and I hate riding on soft tyres. I have had them so soft it was like riding on a bouncy castle but not enough to bottom out... that would be worse but still :evil:
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Re: tyre pressures, what causes the loss?

Postby VRE » Wed Sep 25, 2013 1:55 pm

I think nitrous oxide filled tyres are the way to go. At least then if a leak develops, you can have a bit of a giggle about it :wink: .
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Re: tyre pressures, what causes the loss?

Postby gorilla monsoon » Wed Sep 25, 2013 4:38 pm

HappyHumber wrote:
DavidI wrote:
bychosis wrote:I thought it was the gremlins that come out at night and steal single socks and pens, if you haven't got any pens or pairs of socks they let a bit of air out of your tyres.
Maybe it's the Underpants Gnomes?

God forbid they should ever cross polinate with the Puncture Fairy.


There's puncture fairies? :shock: Damn, I thought it was invisible rats!
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Re: tyre pressures, what causes the loss?

Postby gorilla monsoon » Wed Sep 25, 2013 4:39 pm

casual_cyclist wrote:
DoubleSpeeded wrote:a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

Mine don't :evil: I have to check them every couple of months and most of the time they have gone down a little.
I don't check my bike tyres enough and I hate riding on soft tyres. I have had them so soft it was like riding on a bouncy castle but not enough to bottom out... that would be worse but still :evil:


You check your car tyres once every two months? You should be checking them once a week. Do you know the financial and safety issues of running under-inflated tyres?
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Re: tyre pressures, what causes the loss?

Postby il padrone » Wed Sep 25, 2013 6:20 pm

casual_cyclist wrote:
DoubleSpeeded wrote:a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

Mine don't :evil: I have to check them every couple of months and most of the time they have gone down a little.
I don't check my bike tyres enough and I hate riding on soft tyres. I have had them so soft it was like riding on a bouncy castle but not enough to bottom out... that would be worse but still :evil:

Chances are you are probably OK, and many cyclists are riding over-inflated tyres. At least going by Frank Berto and the 15% drop ideal. Check your wheel loads and tyre pressure to get 15% drop. You may well be surprised.

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Re: tyre pressures, what causes the loss?

Postby casual_cyclist » Wed Sep 25, 2013 6:51 pm

gorilla monsoon wrote:
casual_cyclist wrote:
DoubleSpeeded wrote:a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

Mine don't :evil: I have to check them every couple of months and most of the time they have gone down a little.
I don't check my bike tyres enough and I hate riding on soft tyres. I have had them so soft it was like riding on a bouncy castle but not enough to bottom out... that would be worse but still :evil:


You check your car tyres once every two months? You should be checking them once a week. Do you know the financial and safety issues of running under-inflated tyres?

At the amount of kilometres I drive... zero. I primarily cycle, catch public transport or walk. Driving is a last resort for me.
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Re: tyre pressures, what causes the loss?

Postby casual_cyclist » Wed Sep 25, 2013 6:54 pm

il padrone wrote:
casual_cyclist wrote:
DoubleSpeeded wrote:a car tyre holds pressure very well, when its clinched with a steel or alloy rim?

Mine don't :evil: I have to check them every couple of months and most of the time they have gone down a little.
I don't check my bike tyres enough and I hate riding on soft tyres. I have had them so soft it was like riding on a bouncy castle but not enough to bottom out... that would be worse but still :evil:

Chances are you are probably OK, and many cyclists are riding over-inflated tyres. At least going by Frank Berto and the 15% drop ideal. Check your wheel loads and tyre pressure to get 15% drop. You may well be surprised.

Gaa! That doesn't help! I am running 32's and my bike and me are close to the 100kg mark. I run mine around 80 psi which is lower than the chart recommends. :(
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Re: tyre pressures, what causes the loss?

Postby kb » Thu Sep 26, 2013 8:33 am

casual_cyclist wrote:Gaa! That doesn't help! I am running 32's and my bike and me are close to the 100kg mark. I run mine around 80 psi which is lower than the chart recommends. :(

You may have forgotten to split your weight over two wheels.
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Re: tyre pressures, what causes the loss?

Postby VRE » Thu Sep 26, 2013 8:48 am

kb wrote:
casual_cyclist wrote:Gaa! That doesn't help! I am running 32's and my bike and me are close to the 100kg mark. I run mine around 80 psi which is lower than the chart recommends. :(

You may have forgotten to split your weight over two wheels.

Plus it's about a 60% rear vs 40% front split, so the pressures to use on the 2 tyres will typically be different.
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