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 05-24-08, 10:38 PM   #1
drainyoo
Senior Member
Thread Starter
 
Join Date: Oct 2007
Location: NYC
Bikes: Capo
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Inconsistent tire pressure

My road tires seem like they can't hold their pressure. I will pump them up to about 110psi and then two days later the pressure is around 80psi. It seems like I have to pump it up before every ride. Is this normal?
drainyoo is offline   Reply With Quote
Old 05-24-08, 10:57 PM   #2
Bill Kapaun
Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.
Posts: 9,496
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 125 Post(s)
Yep
Bill Kapaun is offline   Reply With Quote
Old 05-25-08, 12:32 AM   #3
wmodavis
Bill
 
Join Date: May 2007
Location: HIGHLANDS RANCH, CO
Bikes: Specialized Globe Sport, Specialized Stumpjumper FSR Pro
Posts: 630
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
High pressure, low volume, it doesn't take much require refil. It's really not that hard, just make it a habit to check before each ride.
wmodavis is offline   Reply With Quote
Old 05-25-08, 01:44 AM   #4
markjenn
Senior Member
 
Join Date: Aug 2006
Bikes:
Posts: 929
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
30 psi loss in two days is outside normal leakdown rates in my book. Are you sure you're really losing this much? On low-volume road tires, it's pretty hard to check a tire without losing 5-10 psi.

I lose about 20 psi over two weeks or so.

- Mark
markjenn is offline   Reply With Quote
Old 05-25-08, 02:05 AM   #5
Ziemas
Senior Member
 
Ziemas's Avatar
 
Join Date: Nov 2004
Location: Riga, Latvia
Bikes:
Posts: 10,082
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Check that the valve cores are screwed in tight. Recently I've come across a bunch of tubes in which were leaking air from the valves. A spit test should tell you if they are leaking. I fixed mine with some blue LokTite on the threads of the valve core and none of them have leaked since.
Ziemas is offline   Reply With Quote
Old 05-25-08, 07:04 AM   #6
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: 29,117
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 179 Post(s)
How are you determining the tire pressure? As mentioned, high pressure/low volume of bike tires can lose significant pressure just from using the pressure gauge.

It's the "Heisenberg Uncertainty Principle" applied to bikes; the more you look, the less you know.
HillRider is offline   Reply With Quote
Old 05-25-08, 07:52 AM   #7
Longfemur
Senior Member
 
Join Date: Aug 2005
Bikes:
Posts: 1,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Yes. It depends on the tubes. Lighter tubes seem to lose pressure more quickly.
Longfemur is offline   Reply With Quote
Old 05-25-08, 08:07 AM   #8
sch
Senior Member
 
Join Date: May 2003
Location: Mountain Brook. AL
Bikes:
Posts: 3,086
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 42 Post(s)
Butyl hold air much better than latex. That is a normal to slow leak rate for latex
tubes. Butyl vary a lot, new ones on our tandem lose less than a #/day, others
in the stable with more mileage can lose 3-5#/day. You may have a micro pinhole.
Doesn't take much of a hole to lose at 10-15#/day. Or a leaky valve.
sch is offline   Reply With Quote
Old 05-25-08, 02:23 PM   #9
RussB
Senior Member
 
RussB's Avatar
 
Join Date: Sep 2006
Location: Millis, MA
Bikes: 2015 Trek Domane 5.2
Posts: 296
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I typically lose pressure from 110 to 80 psi in about 4 days (both tires). This is because of the porous nature bike tubes and the high pressure.
RussB is offline   Reply With Quote
Old 05-25-08, 03:12 PM   #10
drainyoo
Senior Member
Thread Starter
 
Join Date: Oct 2007
Location: NYC
Bikes: Capo
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
To check the pressure I use a floor pump which as a gauge included. The valve cores are always screwed in tight. I'll keep an eye on it some more but what is a normal amount of lose for 2 days?
drainyoo is offline   Reply With Quote
Old 05-25-08, 03:17 PM   #11
Geoff326
Senior Member
 
Geoff326's Avatar
 
Join Date: Apr 2005
Location: Alameda, CA
Bikes: Cannondale CAAD7
Posts: 1,093
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I always wondered how much air pressure u lose just by attaching the pump to your valve.

I guess you could find out by pumping up ur tire, noting the pressure, removing the pump, then reattaching it to see what the pressure is then.
Geoff326 is offline   Reply With Quote
Old 05-25-08, 04:26 PM   #12
markjenn
Senior Member
 
Join Date: Aug 2006
Bikes:
Posts: 929
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
I think the leakdown rate varies a lot, but 15% a day is excessive and not normal, at least not with the common tubes and tires I've been using for decades. I did a little math based on my experience where a tire with 110 psi will be down into the 80's in a week or so and it comes out something like 3% per day.

Again, you lose a lot of air just checking with gauge, or hooking up a pump, so unless you do some experiments to correct for this, I think you always tend to over-estimate the loss. A typical scenario is that a person gets ready to go for a ride and the bike has been sitting a few days. They check the tires by hand and they feel slightly soft (they're down maybe 5-10 psi), so they hook up the floor pump and in the process of doing so, they lose more air and the gauge on the pump reads 80. That doesn't mean they lost 30 psi.

But if riding the bike with the tires down that 5-10 psi matters to you, then you do probably need to fill them every few days which may mean every ride.

Personally, I've found that the tradeoff between ride quality and rolling resistance is about an even one for me, so I don't mind if the tires are down 10 psi on a given ride - I just pedal slightly harder and enjoy the better ride.

- Mark
markjenn is offline   Reply With Quote
Old 05-25-08, 08:08 PM   #13
ScrubJ
Senior Member
 
Join Date: Apr 2006
Location: Vero Beach FL
Bikes:
Posts: 1,102
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Would be normal in my book
ScrubJ is offline   Reply With Quote
Old 05-25-08, 08:34 PM   #14
DieselDan
Senior Member
 
DieselDan's Avatar
 
Join Date: Mar 2003
Location: Beaufort, South Carolina, USA and surrounding islands.
Bikes: Cannondale R500, Motobecane Messenger
Posts: 8,521
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Normal. Don't expect the laws of chemistry to change for you. If topping off tire pressure is too much, then consider something other then cycling.
DieselDan is offline   Reply With Quote
Old 05-25-08, 08:58 PM   #15
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)
I think it's close to normal. I ride at about 118 in the rear tire and 110 in the front and my wife rides at 5 pounds less than that due to her lighter weight. We'll lose 10 pounds in the first day, then 5 the second, and gradually lose less and less with more time. I always top off our tires immediately before each and every ride. It's easy to damage a presta valve by tightening it too much. All you need to do is snug the nut down to keep the dirt out. The pressure inside the tire should keep the valve closed.

Al
Al1943 is offline   Reply With Quote
Old 05-25-08, 09:24 PM   #16
Longfemur
Senior Member
 
Join Date: Aug 2005
Bikes:
Posts: 1,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
You shouldn't lose any pressure just by putting the pump head on a Presta valve, unless you're pushing the valve down or bending it sideways as you're doing it (poor technique). That's the whole purpose of Prestas. The valve doesn't actually open until you put some air pressure on it.
Longfemur is offline   Reply With Quote
Old 05-26-08, 09:09 AM   #17
drainyoo
Senior Member
Thread Starter
 
Join Date: Oct 2007
Location: NYC
Bikes: Capo
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by DieselDan View Post
Normal. Don't expect the laws of chemistry to change for you. If topping off tire pressure is too much, then consider something other then cycling.
I have no problems filling up my tires before each ride. I just wanted to see if it was normal or not.
drainyoo is offline   Reply With Quote
Old 05-26-08, 03:46 PM   #18
Artmo
Senior Member
 
Join Date: Feb 2005
Location: SW Florida
Bikes: '04 Trek 2300; '06 Bianchi Pista; '57 Maclean; '10 Scott CR1 Pro; 2005 Trek 2000 Tandem; '09 Comotion Macchiato Tandem; 199? Novara Road; 2014 Cannondale T2 tandem
Posts: 1,294
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 16 Post(s)
Quote:
Originally Posted by drainyoo View Post
My road tires seem like they can't hold their pressure. I will pump them up to about 110psi and then two days later the pressure is around 80psi. It seems like I have to pump it up before every ride. Is this normal?
I find the same. It's much worse if you pump with a CO2 cartridge because CO2 permeates
butyl rubber much faster than N2 which is the main component of air. If you don't want to keep inflating your tires, use pure nitrogen as some car tire fitters do.
Artmo 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 04:19 AM.