Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-22-09, 09:41 AM   #1
PatrickJIV
Senior Member
Thread Starter
 
PatrickJIV's Avatar
 
Join Date: Mar 2009
Location: Mobile, AL
Bikes: Schwinn Sidewinder
Posts: 75
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Where does the air go?

Can't understand why my tires leak air. Lose about 10#psi per month. Both tires are slime filled, valve is not leaking at all....so....where does the air go?
PatrickJIV is offline   Reply With Quote
Old 10-22-09, 09:43 AM   #2
garysol1 
Senior Member
 
garysol1's Avatar
 
Join Date: Apr 2005
Location: K-Zoo Michigan
Bikes:
Posts: 10,139
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
10psi loss per month is nothing. The air especially when under pressure simply finds its way through the rubber tube and is released. Perfectly normal.
__________________
Trek Emonda SLR8 USA Built
Trek Stache 7 Its a hoot!
Specialized AWOL Mile Muncher
Specialized Fatboy Trail Miles of Smiles
Kona Jake The Snake Cross
garysol1 is offline   Reply With Quote
Old 10-22-09, 09:51 AM   #3
prathmann
Senior Member
 
Join Date: Nov 2008
Location: Bay Area, Calif.
Bikes:
Posts: 6,224
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 150 Post(s)
Yes, there's a slow diffusion of air molecules through the walls of the rubber tubes. Heavier, thicker tubes will lose air more slowly. CO2 will diffuse through much quicker than regular air. And if you're really concerned then you could use pure nitrogen which escapes a little slower than the oxygen in the air (21% oxygen, 78% nitrogen, 1% argon and others - plus a variable amount of water vapor).
prathmann is offline   Reply With Quote
Old 10-22-09, 09:52 AM   #4
old and new
Senior Member
 
Join Date: Mar 2007
Bikes:
Posts: 3,134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Porosity ... Tubes, though they hold air very effectively, seep air. Air sneaks out through the bead occassionally too going over bumps.
10 lbs. is about avg. per month, better than.. if you frequently ride.
I've had bikes idle for many months and had only a little loss. Others required routine topping-off. In which case, tubes were changed.
There IS a point though where the air escapes at a reduced rate.
Cars are a good example; less pressure (especially when u.infl.) with plenty of volume. Bikes have Hi-Press, low volume. Golf Carts have neither.
If you routinely kept your bike tires too low, they would lose less.
old and new is offline   Reply With Quote
Old 10-22-09, 12:50 PM   #5
PatrickJIV
Senior Member
Thread Starter
 
PatrickJIV's Avatar
 
Join Date: Mar 2009
Location: Mobile, AL
Bikes: Schwinn Sidewinder
Posts: 75
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Very informative answers from all, and I thank everyone!
PatrickJIV is offline   Reply With Quote
Old 10-23-09, 03:59 AM   #6
griftereck
Senior Member
 
Join Date: Jun 2008
Location: angus scotland
Bikes: Grifter BSA 20
Posts: 600
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Ive taken tubes from cheap bikes. checked them in a bucket of water for leaks.
the tubes take on a silvery sheen as theres lots of cracks in the tube. where the airs escaping. Its not big enough holes to do big bubbles that escape quickly.
griftereck is offline   Reply With Quote
Old 10-23-09, 06:21 AM   #7
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 29,113
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 178 Post(s)
Quote:
Originally Posted by old and new View Post
Air sneaks out through the bead occassionally too going over bumps.
Only if you use tubeless tires. Innertubes don't leak from bumps unless they are severe enough to cause a "snakebite" puncture.

Quote:
Originally Posted by old and new View Post
There IS a point though where the air escapes at a reduced rate. Cars are a good example; less pressure (especially when u.infl.) with plenty of volume.
The other thing car tires have is a much longer diffusion path since the tread and side walls are much thicker than a bike innertube. The further the air molecules have to go the slower they diffuse out.
HillRider is offline   Reply With Quote
Old 10-23-09, 08:36 AM   #8
neil0502
My bike's better than me!
 
neil0502's Avatar
 
Join Date: Feb 2005
Location: Northern Colorado
Bikes: (2) Moots Vamoots, (1) Cannondale T2000 tourer, (1) Diamondback Response Comp mtb
Posts: 2,041
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
It's a well-known fact that the air goes to Fresno, California.

HTH.
neil0502 is offline   Reply With Quote
Old 10-25-09, 11:52 AM   #9
CloudyBright
Back on Bikes at 53!
 
Join Date: Apr 2009
Bikes:
Posts: 33
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
All very good reasons why one shouldn't simply apply test results of how nitrogen works in car tires, to bicycle tires.

Bicycles tires have: 1. A much smaller volume of air for the rubber surface area
2. Thinner rubber
3. Higher pressures, except perhaps for the largest "balloon" type tires

For myself, all my bike tires are in the 35-47mm range, 80psi tops in the rears, I just pump up with air. If I had nitrogen around for some other reason, I'd use it, but won't go to the trouble & expense just for the bikes
CloudyBright is offline   Reply With Quote
Old 10-25-09, 08:46 PM   #10
Al1943
Senior Member
 
Join Date: Feb 2005
Location: Oklahoma
Bikes: Trek 5500, Colnago C-50
Posts: 9,433
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by PatrickJIV View Post
Can't understand why my tires leak air. Lose about 10#psi per month. Both tires are slime filled, valve is not leaking at all....so....where does the air go?
A 10 pound loss in a couple of days is normal for high pressure road bike tires. They need to be fully inflated before each ride.

Al
Al1943 is offline   Reply With Quote
Old 10-26-09, 07:55 AM   #11
SlimAgainSoon
Senior Member
 
SlimAgainSoon's Avatar
 
Join Date: Sep 2006
Location: Down South
Bikes:
Posts: 1,261
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
10-lbs. a month -- a lose more air than that in a week.

You must have good tubes.
SlimAgainSoon is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 07:24 AM.