Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

how to measure a top tube diameter?

Notices
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.

how to measure a top tube diameter?

Old 07-23-20, 07:33 AM
  #1  
erbfarm
Senior Member
Thread Starter
 
Join Date: Aug 2007
Location: Portland, OR
Posts: 426
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
Liked 1 Time in 1 Post
how to measure a top tube diameter?

Hi all

I'm swapping cantis for V brakes on my 1990's mountain bike and need to do some cable re-routing by adding a cable stop to my frame. How do I measure the diameter of the top tube so I know which size to buy? The options for the cable stop are 31.8 or 34.9.

Thanks!
erbfarm is offline  
Old 07-23-20, 07:38 AM
  #2  
billridesbikes
Senior Member
 
Join Date: Nov 2019
Posts: 220
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 69 Post(s)
Liked 133 Times in 78 Posts
Um, calipers?

If you don’t have calipers measure around the tube with a tape measure and divide by 3.14, that is also the diameter.
billridesbikes is offline  
Likes For billridesbikes:
Old 07-23-20, 07:40 AM
  #3  
Phil_gretz
Journeyman Bike Commuter
 
Phil_gretz's Avatar
 
Join Date: Aug 2009
Location: Alexandria, VA
Posts: 5,903

Bikes: '71 Jeunet 640, '74 Fuji Special Road Racer, '79 Peugeot PXN10LE, '88 Fuji Saratoga, '13 Motobecane Fantom29 HT, '16 Motobecane Turino Pro Disc, '16 Motobecane Gran Premio Elite, '18 Velobuild VB-R-022

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 979 Post(s)
Liked 627 Times in 354 Posts
Digital calipers. A 1990s mountain bike could be anything from 28.6mm upward. Photo?
Phil_gretz is offline  
Old 07-23-20, 07:42 AM
  #4  
dedhed
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 6,815

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400

Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 1302 Post(s)
Liked 707 Times in 487 Posts
Are the tubes round?
dedhed is offline  
Old 07-23-20, 07:44 AM
  #5  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,790

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1039 Post(s)
Liked 241 Times in 178 Posts
Originally Posted by Phil_gretz View Post
Digital calipers. A 1990s mountain bike could be anything from 28.6mm upward. Photo?
Hey, Phil, they don't have to be digital! One could use a dial or even an old vernier caliper, some of which were more accurate than the current ChinCom offerings at Harbor Fright.

I own an old Starrett 123 Vernier Caliper. Very accurate. Looks like the one below:


WizardOfBoz is offline  
Likes For WizardOfBoz:
Old 07-23-20, 07:46 AM
  #6  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 13,783

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2496 Post(s)
Liked 567 Times in 438 Posts
If you don't have a caliper then take a piece of paper and cut out a square from one edge. The square might be 1", 1 1/8" or 1 1/4". Then place this gage over the tube and see which fits right. That's the tube's diameter.

Or wrap a piece of paper around the tube and mark on it where it meets back up with the start of the piece. This is the tube's circumference. Measure this with a ruler and divide by Pi (3.1415) So a 1" tube has a circumference of 3,1415", a 1 1/18" tube is 3.53" and a 1 1/14" tube will be about 3.93".

This is simple 8th grade math. Andy.
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 07-23-20, 07:47 AM
  #7  
HillRider
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 32,253

Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!

Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 1438 Post(s)
Likes: 0
Liked 260 Times in 209 Posts
If you don't have a metric caliper or even a metric ruler these are the inch equivalents:

1-1/8" = 28.6 mm
1-1/4" = 31.8 mm
1-3/8" = 34.9 mm

As long as your top tube is round it is very likely to be one of these three diameters.
HillRider is offline  
Old 07-23-20, 07:50 AM
  #8  
HillRider
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 32,253

Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!

Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 1438 Post(s)
Likes: 0
Liked 260 Times in 209 Posts
Originally Posted by Andrew R Stewart View Post
This is simple 8th grade math. Andy.
Andy, it was when we were in 8th grade. Maybe not so much any more.
HillRider is offline  
Likes For HillRider:
Old 07-23-20, 08:10 AM
  #9  
Koyote
Senior Member
 
Join Date: Sep 2017
Posts: 1,968
Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1076 Post(s)
Liked 1,098 Times in 528 Posts
Originally Posted by billridesbikes View Post
Um, calipers?

If you donít have calipers measure around the tube with a tape measure and divide by 3.14, that is also the diameter.
Originally Posted by Andrew R Stewart View Post
If you don't have a caliper then take a piece of paper and cut out a square from one edge. The square might be 1", 1 1/8" or 1 1/4". Then place this gage over the tube and see which fits right. That's the tube's diameter.

Or wrap a piece of paper around the tube and mark on it where it meets back up with the start of the piece. This is the tube's circumference. Measure this with a ruler and divide by Pi (3.1415) So a 1" tube has a circumference of 3,1415", a 1 1/18" tube is 3.53" and a 1 1/14" tube will be about 3.93".

This is simple 8th grade math. Andy.
And yet, the vast majority of adults would have no idea what you guys are talking about...Which is a sad commentary.
Koyote is offline  
Likes For Koyote:
Old 07-23-20, 09:14 AM
  #10  
Retro Grouch 
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 29,930

Bikes: Catrike 559 I own some others but they don't get ridden very much.

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1446 Post(s)
Liked 356 Times in 218 Posts
Originally Posted by erbfarm View Post
The options for the cable stop are 31.8 or 34.9.
Those are your options so you don't have to be super accurate, you only have to know which (if either) will fit your bike.

If you have a big Crescent wrench, tighten it loosely around your tube like you would a caliper and measure the distance between the jaws. It'll be accurate enough for your needs.

Where did you find V-brakes these days? When I was looking a couple of weeks ago, everybody was out of stock.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.
Retro Grouch is offline  
Likes For Retro Grouch:
Old 07-23-20, 09:39 AM
  #11  
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 7,562

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1155 Post(s)
Liked 541 Times in 392 Posts
Originally Posted by HillRider View Post
Andy, it was when we were in 8th grade. Maybe not so much any more.
Who knew math could be so complicated?
dsbrantjr is offline  
Old 07-23-20, 09:41 AM
  #12  
Phil_gretz
Journeyman Bike Commuter
 
Phil_gretz's Avatar
 
Join Date: Aug 2009
Location: Alexandria, VA
Posts: 5,903

Bikes: '71 Jeunet 640, '74 Fuji Special Road Racer, '79 Peugeot PXN10LE, '88 Fuji Saratoga, '13 Motobecane Fantom29 HT, '16 Motobecane Turino Pro Disc, '16 Motobecane Gran Premio Elite, '18 Velobuild VB-R-022

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 979 Post(s)
Liked 627 Times in 354 Posts
Originally Posted by WizardOfBoz View Post
Hey, Phil, they don't have to be digital! One could use a dial or even an old vernier caliper, some of which were more accurate than the current ChinCom offerings at Harbor Fright.

I own an old Starrett 123 Vernier Caliper. Very accurate. Looks like the one below:


Yes!! I remember working with these. Unless you're over 60 years old or a trained machinist, it's unlikely that you can read any non-digital device.
Phil_gretz is offline  
Old 07-23-20, 09:59 AM
  #13  
dedhed
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 6,815

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400

Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 1302 Post(s)
Liked 707 Times in 487 Posts
Originally Posted by Phil_gretz View Post
Yes!! I remember working with these. Unless you're over 60 years old or a trained machinist, it's unlikely that you can read any non-digital device.
My problem as a 60 YO who uses calipers regularly, is my eyes don't let me read a vernier anymore, so everything I own is dial or digital.
I can't imagine reading my vernier transit anymore.
dedhed is offline  
Old 07-23-20, 10:04 AM
  #14  
dedhed
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 6,815

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400

Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 1302 Post(s)
Liked 707 Times in 487 Posts
We use these all the time at work because over 150 years of burying pipe in the water business, diameters have changed and repair parts have to fit.
Mostly the vendors or manufacturer reps give them out as swag.
Come in imperial and metric.

https://www.tigersupplies.com/Produc...217-6653-.aspx
dedhed is offline  
Old 07-23-20, 10:06 AM
  #15  
bikeme
Senior Member
 
Join Date: May 2001
Location: Sunny so. cal.
Posts: 817
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 110 Post(s)
Liked 38 Times in 17 Posts
Originally Posted by billridesbikes View Post
Um, calipers?

If you donít have calipers measure around the tube with a tape measure and divide by 3.14, that is also the diameter.
Math? Who knew it's so handy?! This is a wonderful application of that formula.
bikeme is offline  
Old 07-23-20, 10:13 AM
  #16  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,790

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1039 Post(s)
Liked 241 Times in 178 Posts
The Turnbull circumference tape is nice. I'm familiar with the (very expensive, machinist-oriented) Pi Tape. The tape is has linear measurements (times pi) etched on it. There's an offset and the witness line has verniers. You can read the diameter directly. Work great, but they cost hundreds of bucks. In use:

WizardOfBoz is offline  
Old 07-23-20, 11:15 AM
  #17  
dedhed
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 6,815

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400

Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 1302 Post(s)
Liked 707 Times in 487 Posts
Originally Posted by WizardOfBoz View Post
The Turnbull circumference tape is nice. I'm familiar with the (very expensive, machinist-oriented) Pi Tape. The tape is has linear measurements (times pi) etched on it. There's an offset and the witness line has verniers. You can read the diameter directly. Work great, but they cost hundreds of bucks. In use:
I only need to get to 1/100 of inch so these are close enough especially when measuring crusty old buried stuff. I have a 20' Lufkin tree tape that will let me get to 60" pipe.
https://www.crescenttool.com/measuri...e-measure.html
dedhed is offline  
Old 07-23-20, 12:26 PM
  #18  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,281 Times in 799 Posts
General Tool # 723 calipers are under $10.


https://www.grainger.com/product/54G...1102900020694!
fietsbob is offline  
Old 07-23-20, 01:48 PM
  #19  
vane171
Senior Member
 
Join Date: May 2020
Posts: 153
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 79 Post(s)
Liked 22 Times in 16 Posts
Originally Posted by WizardOfBoz View Post
The Turnbull circumference tape is nice. I'm familiar with the (very expensive, machinist-oriented) Pi Tape. The tape is has linear measurements (times pi) etched on it. There's an offset and the witness line has verniers. You can read the diameter directly. Work great, but they cost hundreds of bucks. In use:

This interesting gizmo I take it you don't need to wrap around a pipe, it is enough to have access to just a part of the pipe's curved body, right?

From the preceding, I like most the spanner wrench method. That's exact enough to make you decide which of the two kinds of diameter you have.

As to calipers, everybody should have one of those cheap plastic ones at minimum that sell for several dollars. I picked up ones with mechanical readout on round dial gradated 1/64th inches, because it was on sale but having grown up in metric world, I still have problems with imperial readouts. Takes me some time squaring it in my head and sometimes I can't make it LOL. Next time I see some good sale on digital, I will get it.

Last edited by vane171; 07-23-20 at 01:58 PM.
vane171 is offline  
Old 07-23-20, 02:17 PM
  #20  
WizardOfBoz
Generally bewildered
 
WizardOfBoz's Avatar
 
Join Date: Aug 2015
Location: Eastern PA, USA
Posts: 2,790

Bikes: 2014 Trek Domane 6.9, 1999 LeMond Zurich, 1978 Schwinn Superior

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1039 Post(s)
Liked 241 Times in 178 Posts
Originally Posted by vane171 View Post
This interesting gizmo I take it you don't need to wrap around a pipe, it is enough to have access to just a part of the pipe's curved body, right?
No, it's a tape measure that you wrap around the object to be measured. The tape is offset (shaped like a "Z") and the scale on the main part of the tape and a Vernier scale on one end. This allows you to get a precision circumference. The circumference is marked in pi(3.14159) inches or centimeters, and so reads directly as diameter.

WizardOfBoz is offline  
Old 07-23-20, 02:42 PM
  #21  
vane171
Senior Member
 
Join Date: May 2020
Posts: 153
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 79 Post(s)
Liked 22 Times in 16 Posts
I can see it would be expensive. If you don't need to be too exact, perhaps there are some devices that estimate the pipe size from a portion of its curved surface. Like if you dig out a pipe only partly and or don't have access to wrap the tape around it.

In past I also resorted to measuring smaller pipe diameter by squeezing two sticks to the sides of it while spreading the free ends with the other hand, so the sticks would be parallel and then measure the distance between the sticks right near the pipe. That give good enough result in most cases but it is handy to have more than two hands... or you can use a rubber band to hold the sticks against the pipe to free one hand for measuring.
vane171 is offline  
Old 07-23-20, 03:28 PM
  #22  
madpogue 
Senior Member
 
Join Date: Jan 2004
Location: Madison, WI USA
Posts: 5,043
Mentioned: 32 Post(s)
Tagged: 0 Thread(s)
Quoted: 1611 Post(s)
Liked 667 Times in 510 Posts
Originally Posted by HillRider View Post
Andy, it was when we were in 8th grade. Maybe not so much any more.
Funny how we've lost our 8th grade math, but we seem to have retained or 8th grade humor.

Originally Posted by dsbrantjr View Post
Who knew math could be so complicated?
madpogue is online now  
Old 07-23-20, 04:34 PM
  #23  
_ForceD_
Senior Member
 
_ForceD_'s Avatar
 
Join Date: Jul 2015
Location: Rhode Island
Posts: 1,389

Bikes: Several...from old junk to new all-carbon.

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 600 Post(s)
Liked 144 Times in 95 Posts
I have calipers. But in lieu of calipers you could do this...then measure across the wrench opening. (Maybe some masking tape on the wrench jaws so you don't scratch your paint.)

Dan

Last edited by _ForceD_; 07-23-20 at 04:40 PM.
_ForceD_ is offline  
Likes For _ForceD_:
Old 07-24-20, 05:56 PM
  #24  
Fissile
Senior Member
 
Fissile's Avatar
 
Join Date: Nov 2007
Posts: 611
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 32 Post(s)
Liked 13 Times in 13 Posts
Originally Posted by _ForceD_ View Post
I have calipers. But in lieu of calipers you could do this...then measure across the wrench opening. (Maybe some masking tape on the wrench jaws so you don't scratch your paint.)

Dan
Redneck calipers! I've done this many times. This method works just fine to measure tube diameter.
Fissile 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


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.