Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

pumping air question

Notices
Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

pumping air question

Old 10-31-09, 07:17 PM
  #1  
Senior Member
Thread Starter
 
avduka's Avatar
 
Join Date: Feb 2009
Posts: 73
Likes: 0
Liked 0 Times in 0 Posts
pumping air question

I realize it might be a stupid question but I always wonder about it.
Whenever I put air in the tires and I am about to take off the head a lot of air escapes. PSHHHHHH
But I am not sure if this air is actually dropping down the PSI or it's just the air that is between the valve and the head. I get this same PSHHHHHH even if I don't break the seal and try to put air in there but have to take it off because no air is going in.

So basically I always put a few extra PSI just for good measure. I always try to take off the head lightning speed fast so less air escapes.

So if the air getting lost is dropping the PSI, how much extra air do you think is enough?
Discuss
avduka is offline  
Old 10-31-09, 07:42 PM
  #2  
Sputnik - beep beep beep
 
Wake's Avatar
 
Join Date: Oct 2008
Location: Louisville KY
Posts: 481

Bikes: '12 Jamis Coda Elite '09 Jamis Sputnik, '07 Jamis Eclipse, '13 Brompton M6R.

Likes: 0
Liked 1 Time in 1 Post
With presta valves, hardly any air escapes the tube. The air you hear comes from the pump hose. The pump doesn't push on and open the valve like a schrader pump does - it forces air through the valve by over coming the pressure inside the tube.
Wake is offline  
Old 10-31-09, 07:55 PM
  #3  
.....
 
Jynx's Avatar
 
Join Date: Aug 2006
Location: Long Island
Posts: 4,816

Bikes: 2006 Cannondale CAAD8

Likes: 0
Liked 3 Times in 3 Posts
it is air from the pump hose and not the tube.
__________________
Weight Listing Index (Feel Free to add to it!)

Buy your bike parts here
Jynx is offline  
Old 10-31-09, 08:30 PM
  #4  
B+ roadie I guess?
 
acaurora's Avatar
 
Join Date: Jul 2009
Location: Roseville, CA
Posts: 1,287

Bikes: 2013 BMC GranFondo GF01 Ui2

Likes: 0
Liked 0 Times in 0 Posts
That wooshing of air, as everyone said, is the air coming from your pump, not the tire. It shouldn't be substantial, and therefore is very minor.
acaurora is offline  
Old 10-31-09, 11:37 PM
  #5  
Senior Member
Thread Starter
 
avduka's Avatar
 
Join Date: Feb 2009
Posts: 73
Likes: 0
Liked 0 Times in 0 Posts
awesome thanks
avduka is offline  
Old 12-04-09, 10:07 AM
  #6  
Senior Member
 
Megiddo's Avatar
 
Join Date: Sep 2009
Location: HdG, MD
Posts: 197
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Wake
The pump doesn't push on and open the valve like a schrader pump does - it forces air through the valve by over coming the pressure inside the tube.
I was looking (search feature worked!) for why my pump wouldn't add air? I just got my new bike last night and only put 100lbs in the tires intending to add the next 20lbs today. Well, dang the pump seemed stuck (like it does on schrader valves). Being new to presta valves, I was stuck!

Thanks WAKE for the tip!
Megiddo is offline  
Old 12-04-09, 10:14 AM
  #7  
Primate
 
Metzinger's Avatar
 
Join Date: Jan 2006
Location: gone
Posts: 2,579

Bikes: Concorde Columbus SL, Rocky Mountain Edge, Sparta stadfiets

Likes: 0
Liked 5 Times in 5 Posts
If the pump had no valve before the hose, the air in the hose would push the handle back up after the bottom of each stroke.
Metzinger is offline  
Old 12-04-09, 10:42 AM
  #8  
Senior Member
 
Megiddo's Avatar
 
Join Date: Sep 2009
Location: HdG, MD
Posts: 197
Likes: 0
Liked 0 Times in 0 Posts
The handle didn't pop back up, but it had that strange feeling like schrader valves do when you don't have it connected correctly. It didn't behave correctly until I went past the 100lbs which I had done the previous night.

All is good now.
Megiddo is offline  
Old 12-04-09, 12:29 PM
  #9  
Senior Member
 
Mansram01's Avatar
 
Join Date: May 2007
Location: Los Angeles, CA
Posts: 1,344

Bikes: '17 Trek Emonda, '16 Yeti ASR5, '14 Cdale F29 '08 Orbea Orca.

Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Wake
With presta valves, hardly any air escapes the tube. The air you hear comes from the pump hose. The pump doesn't push on and open the valve like a schrader pump does - it forces air through the valve by over coming the pressure inside the tube.
Good info, Wake. I already knew that the air was from the hose but didn't know how exactly the valve on a Presta worked. Cool deal.
Mansram01 is offline  
Old 12-04-09, 01:03 PM
  #10  
ride lots be safe
 
Creakyknees's Avatar
 
Join Date: Jan 2007
Location: Texas
Posts: 5,224
Likes: 0
Liked 1 Time in 1 Post
/ idly wondering when / if riders will ever figure out that more pressure is not better...
Creakyknees is offline  
Old 12-04-09, 01:07 PM
  #11  
Galveston County Texas
 
10 Wheels's Avatar
 
Join Date: Nov 2007
Location: In The Wind
Posts: 33,280

Bikes: 02 GTO, 2011 Magnum

Liked 1,255 Times in 631 Posts
Originally Posted by Creakyknees
/ idly wondering when / if riders will ever figure out that more pressure is not better...
Max PSI is more efficient.
__________________
Fred "The Real Fred"

10 Wheels is offline  
Old 12-04-09, 01:12 PM
  #12  
Type 1 Racer
 
rydaddy's Avatar
 
Join Date: Apr 2006
Location: Davis, CA
Posts: 2,579

Bikes: A dozen or so.

Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by 10 Wheels
Max PSI is more efficient.
Here we go again...

Last edited by rydaddy; 12-04-09 at 01:17 PM.
rydaddy is offline  
Old 12-04-09, 01:20 PM
  #13  
Galveston County Texas
 
10 Wheels's Avatar
 
Join Date: Nov 2007
Location: In The Wind
Posts: 33,280

Bikes: 02 GTO, 2011 Magnum

Liked 1,255 Times in 631 Posts
Originally Posted by rydaddy
Here we go again...
Simple test for simple people.
Take basketball, bounce it with low psi, then bounce it with high psi.
Which gives more bounce? Which take Less Effort to get a high bounce?
__________________
Fred "The Real Fred"

10 Wheels is offline  
Old 12-04-09, 01:23 PM
  #14  
Type 1 Racer
 
rydaddy's Avatar
 
Join Date: Apr 2006
Location: Davis, CA
Posts: 2,579

Bikes: A dozen or so.

Likes: 0
Liked 0 Times in 0 Posts
Your simple minded approach is flawed. I don't bounce my wheels very often anyway.
rydaddy is offline  
Old 12-04-09, 01:25 PM
  #15  
Galveston County Texas
 
10 Wheels's Avatar
 
Join Date: Nov 2007
Location: In The Wind
Posts: 33,280

Bikes: 02 GTO, 2011 Magnum

Liked 1,255 Times in 631 Posts
Originally Posted by rydaddy
Your simple minded approach is flawed.
Take the same test and see how far a basketball will roll down a flat road.
__________________
Fred "The Real Fred"

10 Wheels is offline  
Old 12-04-09, 01:28 PM
  #16  
Type 1 Racer
 
rydaddy's Avatar
 
Join Date: Apr 2006
Location: Davis, CA
Posts: 2,579

Bikes: A dozen or so.

Likes: 0
Liked 0 Times in 0 Posts
The higher psi ball will bounce higher. Just like an overly inflated tire will bounce more off road imperfections, making it less efficient. Shocking, I know.
rydaddy is offline  
Old 12-04-09, 01:33 PM
  #17  
Galveston County Texas
 
10 Wheels's Avatar
 
Join Date: Nov 2007
Location: In The Wind
Posts: 33,280

Bikes: 02 GTO, 2011 Magnum

Liked 1,255 Times in 631 Posts
Originally Posted by rydaddy
The higher psi ball will bounce higher. Just like an overly inflated tire will bounce more off road imperfections, making it less efficient. Shocking, I know.
Not True. It takes less effort to bounce a ball with high PSI.

Find a long gradual down hill.
Start at the top with your bike with Max PSI in the tires.
Start with a small push.
Do the same with Low PSI.

Which PSI will coast the farthest?
__________________
Fred "The Real Fred"

10 Wheels is offline  
Old 12-04-09, 01:36 PM
  #18  
Type 1 Racer
 
rydaddy's Avatar
 
Join Date: Apr 2006
Location: Davis, CA
Posts: 2,579

Bikes: A dozen or so.

Likes: 0
Liked 0 Times in 0 Posts
I'm speechless.
rydaddy is offline  
Old 12-04-09, 01:51 PM
  #19  
Elite Fred
 
mollusk's Avatar
 
Join Date: Aug 2005
Location: Edge City
Posts: 10,945

Bikes: 2009 Spooky (cracked frame), 2006 Curtlo, 2002 Lemond (current race bike) Zurich, 1987 Serotta Colorado, 1986 Cannondale for commuting, a 1984 Cannondale on loan to my son

Liked 43 Times in 19 Posts
Originally Posted by 10 Wheels
Not True. It takes less effort to bounce a ball with high PSI.

Find a long gradual down hill.
Start at the top with your bike with Max PSI in the tires.
Start with a small push.
Do the same with Low PSI.

Which PSI will coast the farthest?
So, why don't you ride on solid rubber tires?
mollusk is offline  
Old 12-04-09, 02:01 PM
  #20  
slow up hills
 
kudude's Avatar
 
Join Date: Mar 2006
Location: Seattle, WA
Posts: 4,931

Bikes: Giant TCR, Redline CX, Ritchey Breakaway, Spec S-works epic

Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by 10 Wheels
Not True. It takes less effort to bounce a ball with high PSI.

Find a long gradual down hill.
Start at the top with your bike with Max PSI in the tires.
Start with a small push.
Do the same with Low PSI.

Which PSI will coast the farthest?
you get more leniency since you ride more than anyone else (I'm thinking of the right guy, yeah?)

On a wooden velodrome, by all means, pump 'em up to 160psi. In the real world of chipseal and asphalt, rydaddy's right. Yes, there seems to be more rolling resistance (by a tiny fraction), but forcing your body to absorb every single pebble is NOT the reason for pneumatic tubes.

edit: I'm advocating for ~100psi as opposed to 140psi. I'm not in favor of 75 or anything like that for 23c tires
kudude is offline  
Old 12-04-09, 02:17 PM
  #21  
umd
Banned
 
umd's Avatar
 
Join Date: Sep 2005
Location: Santa Barbara, CA
Posts: 28,387

Bikes: Specialized Tarmac SL2, Specialized Tarmac SL, Giant TCR Composite, Specialized StumpJumper Expert HT

Likes: 0
Liked 3 Times in 3 Posts
Originally Posted by 10 Wheels
Simple test for simple people.
Take basketball, bounce it with low psi, then bounce it with high psi.
Which gives more bounce? Which take Less Effort to get a high bounce?
Epic fail
umd is offline  
Old 12-04-09, 02:33 PM
  #22  
¯\_(ツ)_/¯
 
Ygduf's Avatar
 
Join Date: Jun 2008
Location: Redwood City, CA
Posts: 10,978

Bikes: aggressive agreement is what I ride.

Likes: 0
Liked 4 Times in 4 Posts
Originally Posted by 10 Wheels
Not True. It takes less effort to bounce a ball with high PSI.

Find a long gradual down hill.
Start at the top with your bike with Max PSI in the tires.
Start with a small push.
Do the same with Low PSI.

Which PSI will coast the farthest?
Know what has less rolling resistance than a rubber tire? An alloy rim. Why do you think train wheels are metal?
Ygduf is offline  
Old 12-04-09, 05:26 PM
  #23  
umd
Banned
 
umd's Avatar
 
Join Date: Sep 2005
Location: Santa Barbara, CA
Posts: 28,387

Bikes: Specialized Tarmac SL2, Specialized Tarmac SL, Giant TCR Composite, Specialized StumpJumper Expert HT

Likes: 0
Liked 3 Times in 3 Posts
Originally Posted by kudude
you get more leniency since you ride more than anyone else (I'm thinking of the right guy, yeah?)
If his bikejournal profile is correct we are pretty much even.
umd is offline  

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Your Privacy Choices -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.