Anyone know the typical tire deflation rate through osmosis?

[coolpeople]

I've got a GT300i with Pirellis front and rear. Does anyone know the typical tire deflation rate through osmosis when the tire does not have a hole or defect? I ride my bike several times per week at a minimum. I check the tire pressure monthly or more often and have noticed that it drops several PSI. I air both front and rear to 34 PSI. Thanks guys.

[Mr. Paul]

It is not unusual to lose that much pressure over a month or even less. I could be wrong but it sounds like you are running pressures higher than recommended.  The higher pressure will "squeeze" air out more rapidly until it gets a little closer to the atmospheric  pressure. I try to check mine once a week and it seems I usually put a couple of pounds in. In my experience new tires seem to leak the most.

[coolpeople]

It is not unusual to lose that much pressure over a month or even less. I could be wrong but it sounds like you are running pressures higher than recommended.  The higher pressure will "squeeze" air out more rapidly until it gets a little closer to the atmospheric  pressure. I try to check mine once a week and it seems I usually put a couple of pounds in. In my experience new tires seem to leak the most.

Thanks MP. You are right about the tire pressure being too high. I checked the service manual on cyclepedia, and for solo riding it should be 25.4 psi for both front and rear tires. For two riders the spec is 29 front 32 rear. Thanks for the heads up.

[Mr. Paul]

For solo riding, its 25/28.  Its on page 45 of the PDF. Hope that helps ya.



http://www.kymcousa.com/owners/onroad/People-GT200i-300i-Owners%20Manual.pdf

[Stig / Major Tom]

Three scooters and one motorcycle.....none of them ever lost air.
The only times I've had to add air was to replace the air that came out when fitting the gauge.
My two mechanic buddies confirm my thought that your air is leaking from poor rim   seal or poor valve stem seal. Neither are uncommon faults.
A bit too much air forces a tighter seal....nothing more. A lot more  air can cause a tire's structure to fail.
In short, they say: small leak is due to a small issue. Big leak, etc.
Stig

[Emil]

Just a remark: A tire is loosing air because something is not 100% tight.
Osmosis is the process of a lower concentrated liquid floating through a semi permeable membrane to a higher concentrated liquid.
Just sayin'

As for the air loss I have never found a reliable pattern. Sometimes the pressure would keep up for months, other times it goes down within a few days. That mostly seems to happen though when the temperature changes. I am now checking regularly every 2-3 weeks and after every big temp change, and when the bike stood in the sun for a while. Also 'squeezing' the wheel with the foot ahead of any ride gives me an idea if it's time again for a check.

Cheers,
E.

[Mr. Paul]

Just a remark: A tire is loosing air because something is not 100% tight.
Osmosis is the process of a lower concentrated liquid floating through a semi permeable membrane to a higher concentrated liquid.
Just sayin'

As for the air loss I have never found a reliable pattern. Sometimes the pressure would keep up for months, other times it goes down within a few days. That mostly seems to happen though when the temperature changes. I am now checking regularly every 2-3 weeks and after every big temp change, and when the bike stood in the sun for a while. Also 'squeezing' the wheel with the foot ahead of any ride gives me an idea if it's time again for a check.

Cheers,

I agree with your osmosis point. The air molecules find voids between the rubber and escapes the membrane. Increased pressure increases the evacuation of these molecules until an equilibrium is achieved between the inside and outside pressures. BTW the nitrogen tire inflation that was so popular a few years ago worked to a point because pure nitrogen molecules are larger than the mixed molecules in the ambient air that is usually pumped into a tire. Therefore, less leakage through the permeable layer.
 I have observed the same thing as you, my tires leak. My bicycle tires leak, my car tires leak, my scooter tires leak.

[Emil]

Actually everything is leaking. Memory, wallet, ... even time it seems.
With the scooter I also had the problem that my front valve was bad. Two times this summer my front tire was half flat in the evening.
The ride to the gas station was very interesting. Did you ever ride a scooter with half flat tire? It's ridiculous. Almost uncontrollable. Equivalent to drinking a bottle of Vodka I imagine. Pretty scary actually.