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


Go Back   > >

Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

User Tag List

Reply
 
Thread Tools Search this Thread
Old 08-18-09, 10:24 AM   #1
calbob76
Senior Member
Thread Starter
 
Join Date: Aug 2009
Location: spfd mo
Bikes: big block
Posts: 486
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
tire air/pressure

I've had my masi fixed ltd for about a month now, and I was wondering about tire air. Can I just put some in when it feels low or do I need to measure pressure and stuff?
calbob76 is offline   Reply With Quote
Old 08-18-09, 10:29 AM   #2
ichitz
Nü-Fred
 
ichitz's Avatar
 
Join Date: Jul 2009
Location: Brooklyn, NY
Bikes: Torelli Tipo Uno (stolen), Peugeot Nice, Mercier Kilo TT
Posts: 1,517
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
read ur tires. It will tell u the recommended and max psi.

And u might want to read this.
http://sheldonbrown.com/tires.html
ichitz is offline   Reply With Quote
Old 08-18-09, 10:31 AM   #3
xB_Nutt
Get on your bikes & ride!
 
xB_Nutt's Avatar
 
Join Date: May 2006
Location: Lextown
Bikes: See signature (it varys day to day)
Posts: 1,070
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I reccomend getting a decent floor pump with a gauge and topping the tires off with air before every ride. High pressure, low volume tires will lose a considerable amount of air in a short period of time. The last thing you want to do is get a pinch flat because you didn't have enough air in your tire.
__________________
Litespeed Classic
Soma Double Cross DC
xB_Nutt is offline   Reply With Quote
Old 08-18-09, 10:39 AM   #4
GearsForFears
1. get on 2. pedal
 
Join Date: Jul 2008
Location: Milwaukee
Bikes: '08 Surly Cross-Check SS, '84 Raleigh Alyeska, '00 Mongoose Crossway
Posts: 274
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
When I started commuting rather than riding for leisure I was shocked at how many flats I got right off the bat, not knowing to top the tires. I now fill once a week and it's fine. Filling every ride is better but there's a limit to how much you can eff around every time you get on the bike when the bike is your main transportation.
GearsForFears is offline   Reply With Quote
Old 08-18-09, 10:46 AM   #5
xB_Nutt
Get on your bikes & ride!
 
xB_Nutt's Avatar
 
Join Date: May 2006
Location: Lextown
Bikes: See signature (it varys day to day)
Posts: 1,070
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Good point. If you ride everday then you probably don't need to air up each time. You will learn over time how much air your tires lose per day.
__________________
Litespeed Classic
Soma Double Cross DC
xB_Nutt is offline   Reply With Quote
Old 08-18-09, 10:48 AM   #6
jpdesjar
Guest
 
Bikes:
Posts: n/a
Mentioned: Post(s)
Tagged: Thread(s)
Quoted: Post(s)
I check the tires every week, they hold air pretty well.
  Reply With Quote
Old 08-18-09, 10:48 AM   #7
Ken Cox
King of the Hipsters
 
Join Date: Jan 2005
Location: Bend, Oregon
Bikes: Realm Cycles Custom
Posts: 2,128
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Get a floor pump that has built-in pressure guage, and pump your tires five pounds over pressure every night before you go to sleep.

"Over pressure" doesn't mean over the highest pressure listed on the side of the tire, but, rather, it means over the correct pressure for your body weight.

Let's assume you ride with 700 X 25mm tires.

I specified 25mm instead of 23mm because 25mm most closely corresponds to an inch, and it makes the math easier.

If you weigh 200 pounds, you need a total of 200 pounds of air pressure pushing against the pavement to hold your rims up and away from damaging objects that will pinch flat your tubes and dent your rims.

With a 25mm, or one inch tire, that means each tire should have 100 pounds of pressure pushing against that one inch of contact, so that two tires together would push with 200 pounds of pressure.

If you had a 50mm, or two inch tire, then you would use 50 pounds of pressure, so that two inches times 50 pounds would equal 100 pounds, and two times 100 pounds would equal 200 pounds, your body weight in this example.

Now, to complicate this a little, some of us, maybe most of us, ride with more weight on the rear tire than on the front tire.

For myself, I weigh 225 pounds, and I ride with 125 pounds in the rear and 100 pounds in front.

Every night before I go to sleep, I pump up my rear tire to 130 and my front to 105.

Most people ride with a 23mm tire; close enough to one inch for all the above to apply.
Ken Cox is offline   Reply With Quote
Old 08-18-09, 10:52 AM   #8
queerpunk
aka mattio
 
queerpunk's Avatar
 
Join Date: May 2005
Bikes:
Posts: 6,052
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 52 Post(s)
Quote:
Originally Posted by xB_Nutt View Post
I reccomend getting a decent floor pump with a gauge and topping the tires off with air before every ride. High pressure, low volume tires will lose a considerable amount of air in a short period of time. The last thing you want to do is get a pinch flat because you didn't have enough air in your tire.
Oh man, you're not kidding.

That really is the last thing I want to do.
queerpunk is offline   Reply With Quote
Old 08-18-09, 10:59 AM   #9
Fugazi Dave
Beausage is Beautiful
 
Fugazi Dave's Avatar
 
Join Date: Oct 2003
Location: Chicago, IL
Bikes: 2006 Langster, which I actually like.
Posts: 5,457
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Unneeded pinch flats blow. Even when you maintain your pressure they can happen thanks to ****ty roads. Pinch-flatted at 120 psi the other night on the exposed edge of a manhole cover I couldn't dodge thanks to another crappy bus driver.

A decent floor pump with a gauge is worth the investment and then some. Easy to use and fills a very important need exceptionally well.
Fugazi Dave is offline   Reply With Quote
Old 08-18-09, 12:48 PM   #10
Zachee
DRUNKDRIVER
 
Zachee's Avatar
 
Join Date: Aug 2008
Location: MKE, WI
Bikes: Kilo TT custom
Posts: 315
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
One of the only benefits of weighing only 170 lbs.
Zachee is offline   Reply With Quote
Old 08-18-09, 12:52 PM   #11
GearsForFears
1. get on 2. pedal
 
Join Date: Jul 2008
Location: Milwaukee
Bikes: '08 Surly Cross-Check SS, '84 Raleigh Alyeska, '00 Mongoose Crossway
Posts: 274
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
It does depend on your tires. The ones in my bikes lose 5-10 psi over the week which is manageable with one fill. You will also, over time, learn innate flat-avoiding skills, like scanning the road surface ahead of you for danger spots, and unweighting your saddle and pulling up on the bars when you hit bumps.
GearsForFears is offline   Reply With Quote
Old 08-19-09, 02:59 AM   #12
Fugazi Dave
Beausage is Beautiful
 
Fugazi Dave's Avatar
 
Join Date: Oct 2003
Location: Chicago, IL
Bikes: 2006 Langster, which I actually like.
Posts: 5,457
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Zachee View Post
One of the only benefits of weighing only 170 lbs.
140 here. Definitely a plus.
Fugazi Dave is offline   Reply With Quote
Old 08-19-09, 06:04 AM   #13
Syscrush
Senior Member
 
Syscrush's Avatar
 
Join Date: Feb 2009
Bikes:
Posts: 740
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Quote:
Originally Posted by Ken Cox View Post
I specified 25mm instead of 23mm because 25mm most closely corresponds to an inch, and it makes the math easier.
What really makes the math easier is the way you did it 100% wrong. If you don't know the difference between an inch and a square inch you probably shouldn't be doing your own pressure calculations. According to Sheldon Brown, you're running your tires without enough pressure:

http://www.sheldonbrown.com/tires.html

To the OP, YES you have to "measure pressure and stuff". When you're dealing with high pressure, low volume tires, you can not go by feel. Just top it up once or twice a week with a good floor pump w/integrated gauge and you'll be good to go.
Syscrush is offline   Reply With Quote
Old 08-19-09, 07:28 AM   #14
Ken Cox
King of the Hipsters
 
Join Date: Jan 2005
Location: Bend, Oregon
Bikes: Realm Cycles Custom
Posts: 2,128
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Syscrush
What really makes the math easier is the way you did it 100% wrong. If you don't know the difference between an inch and a square inch you probably shouldn't be doing your own pressure calculations. According to Sheldon Brown, you're running your tires without enough pressure:
Thanks for the link to Sheldon.

I've read what Sheldon has to say on the subject before now, and upon revisiting, what I read confirms that I have exactly the right pressure in my tires.

Perhaps Syscrush can help me see how I misunderstood Sheldon, assuming I misunderstood Sheldon.

By the way, what pressure does Syscrush think I should have in my tires?

I weigh 225 pounds and I have a total, front plus rear, of 225lbs of pressure, and I have this distributed over two one inch contact patches.

I think I did it exactly right.
Ken Cox is offline   Reply With Quote
Old 08-24-09, 06:35 AM   #15
Syscrush
Senior Member
 
Syscrush's Avatar
 
Join Date: Feb 2009
Bikes:
Posts: 740
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
First of all, equating your weight in pounds to tire pressure in psi - and you certainly can't add the pressure in your tires and compare it to your weight.

If your weight is 225 lbs, that's over 100 lbs per wheel, and the link shows that for 100 lbs on a 25mm tire you should be running 110 psi - 120 for a 23mm tire. For ~112 lbs/wheel, your pressure should be more like 135 psi for both wheels if you're running 23's.

If you're going on the assumption that your rear wheel is loaded more heavily (say a 55/45 split), then you'd want something like 120 psi for the front (101 lbs load) and 148 psi (123 lbs load) for the rear. Which would suggest that you may want to step up from the 23's to 25's so you could run 110 front / 136 rear.
Syscrush is offline   Reply With Quote
Old 08-24-09, 07:51 AM   #16
rogwilco
snob
 
rogwilco's Avatar
 
Join Date: Jul 2009
Location: Vienna
Bikes:
Posts: 1,178
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I used to only have a hand pump and just pumped up my tires as much as I could. Then I bought a floor pump and found out that I hadn't put even close to enough pressure into my tires.
rogwilco is offline   Reply With Quote
Old 08-24-09, 09:28 AM   #17
JacoKierkegaard
Fixed-gear roadie
 
JacoKierkegaard's Avatar
 
Join Date: Dec 2008
Location: Wilmington, NC
Bikes: 2008 Masi Speciale Fixed
Posts: 1,048
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
You should use a pump with a gauge. I keep my 700x23's at 140 psi (Clyde here), and by the time they've lost enough air for me to really feel a difference by squeezing the tire they're usually down to about 80. That's nearly half the air gone!
JacoKierkegaard is offline   Reply With Quote
Old 08-24-09, 12:32 PM   #18
t2t2
Member
 
Join Date: May 2009
Bikes:
Posts: 31
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
i remember reading somewhere there's a formula to calculate the best psi base on your weight..anyone remember that?
t2t2 is offline   Reply With Quote
Old 08-24-09, 12:44 PM   #19
ianjk
:)
 
Join Date: Nov 2006
Location: duluth
Bikes: '07 Pista, '09 Fantom Cross Uno, '8? Miyata, '67 Stingray, '0? Zoo mod trials, Tallbike, Chopper, '73 Schwinn Collegiate, '67 Triumph Chopper, '69 CB350, '58 BSA Spitfire, '73 CB450
Posts: 3,392
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by t2t2 View Post
i remember reading somewhere there's a formula to calculate the best psi base on your weight..anyone remember that?
If ride too soft/slow psi++

If ride too hard/rough psi--

If pinch flats occur often psi++

If random catastrophic tube failures psi--

Pretty easy to figure out, IMO way more accurate than some random internet formula.
ianjk is offline   Reply With Quote
Old 08-24-09, 12:49 PM   #20
JacoKierkegaard
Fixed-gear roadie
 
JacoKierkegaard's Avatar
 
Join Date: Dec 2008
Location: Wilmington, NC
Bikes: 2008 Masi Speciale Fixed
Posts: 1,048
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by ianjk View Post
If ride too soft/slow psi++

If ride too hard/rough psi--

If pinch flats occur often psi++

If random catastrophic tube failures psi--

Pretty easy to figure out, IMO way more accurate than some random internet formula.
That's a good way to get things fine tuned, although the internet formulas will give you a good ballpark figure.
JacoKierkegaard is offline   Reply With Quote
Old 08-24-09, 12:52 PM   #21
j3ffr3y
chickenosaurus
 
j3ffr3y's Avatar
 
Join Date: Sep 2008
Location: Boston, MA
Bikes: 2010 Motobecane Team Track, 1997 GT Edge, 2012 Kilo TT Stripper
Posts: 1,189
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by t2t2 View Post
i remember reading somewhere there's a formula to calculate the best psi base on your weight..anyone remember that?
that gives me an idea! I'll write one tonight.
(anyone with windows/a c/c++ compiler can do cross compiles for me?)
j3ffr3y is offline   Reply With Quote
Old 08-24-09, 01:58 PM   #22
Abe Froman
Sausage King
 
Join Date: Feb 2008
Bikes: 2008 Specialized Langster, Kilo WT, 1986 Dahon Classic Folder, 1986 Panasonic Mountain Cat
Posts: 150
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by j3ffr3y View Post
that gives me an idea! I'll write one tonight.
(anyone with windows/a c/c++ compiler can do cross compiles for me?)
Make it an iPhone app!
Abe Froman is offline   Reply With Quote
Old 08-24-09, 02:20 PM   #23
j3ffr3y
chickenosaurus
 
j3ffr3y's Avatar
 
Join Date: Sep 2008
Location: Boston, MA
Bikes: 2010 Motobecane Team Track, 1997 GT Edge, 2012 Kilo TT Stripper
Posts: 1,189
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Abe Froman View Post
Make it an iPhone app!
I don't have an iphone, any willing testers. I'm certainly going to try!
edit: objective cocoa-c? I'll have a look, but I've never used cocoa before.

Last edited by j3ffr3y; 08-24-09 at 02:25 PM.
j3ffr3y is offline   Reply With Quote
Old 08-24-09, 04:18 PM   #24
j3ffr3y
chickenosaurus
 
j3ffr3y's Avatar
 
Join Date: Sep 2008
Location: Boston, MA
Bikes: 2010 Motobecane Team Track, 1997 GT Edge, 2012 Kilo TT Stripper
Posts: 1,189
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
anyone want to build this for windows. I feel that the numbers that I used gives a pretty decent value for a good pressure.
Its really super simple, just plugging in your values to a formula, but w/e, also, it is only for road tires.


EDIT: added to latest post due to error

Last edited by j3ffr3y; 08-24-09 at 05:25 PM.
j3ffr3y is offline   Reply With Quote
Old 08-24-09, 04:41 PM   #25
Syscrush
Senior Member
 
Syscrush's Avatar
 
Join Date: Feb 2009
Bikes:
Posts: 740
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Is that equation correct? It will indicate a lower pressure for a narrower tire, and vice-versa.
Syscrush 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 01:10 AM.