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 09-26-12, 10:15 PM   #1
dabee1106
Member
Thread Starter
 
Join Date: Jun 2009
Bikes:
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Broken Seat Tube

So I was out riding today and the seat tube on my carbon hardtail 29er broke. Is it common for seat tubes to break? Anything that can be done to prevent them from breaking once I get a new frame? Which parts of the bike get stressed the most during riding?
Thanks for your help everyone
dabee1106 is offline   Reply With Quote
Old 09-26-12, 10:25 PM   #2
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 30,824
Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 858 Post(s)
9 out of 10 times (maybe more like 99 out of 100) when a seat tube breaks, it's because the seat post wasn't inserted deep enough. This is true regardless of the frame material.

Many people think that inserting a post up to the minimum insertion line is enough, but that isn't always the case. The min-insert line is related to the post flexing (camming) out of the frame, but doesn't address the needs of modern frame design where the seat tube extends above the top tube. The second consideration which is key to seat tube survival is that the seat post must extend deep enough to end below the bottom of the top tube, preferably an inch or so below that.

Seat tubes break when the post ends above the top tube joint, so all the post's stress is placed on the unsupported section of seat tube above the joint. To protect your next frame , get a longer post, make sure it fits well, and that way the post will buttress the seat tube and take it's fair share of the stress of the rider's shifting weight.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FBinNY is offline   Reply With Quote
Old 09-26-12, 10:47 PM   #3
dabee1106
Member
Thread Starter
 
Join Date: Jun 2009
Bikes:
Posts: 30
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I forgot to say that this seat tube broke below the top tube by about 3 inches.+
dabee1106 is offline   Reply With Quote
Old 09-26-12, 10:57 PM   #4
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 30,824
Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 858 Post(s)
Quote:
Originally Posted by dabee1106 View Post
I forgot to say that this seat tube broke below the top tube by about 3 inches.+
I did leave room for the 1 out of 10 (or 100) that failed for another reason.

There's no reason for a failure there except possibly if a post that ended there was carrying a very heavy rider, or had such a sloppy fit that the end scored the ID of the seat tube. It could also be a function of the details of construction, like if the seat tube had an aluminum liner which ended there, creating a stress riser.

Otherwise it's a fluke, possibly a structural defect, and you shouldn't worry about a repeat in a decent quality frame, unless you weigh upwards of 250#s and maybe shouldn't be riding a carbon frame in the first place.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FBinNY is offline   Reply With Quote
Old 09-27-12, 12:37 AM   #5
catonec 
Senior Member
 
catonec's Avatar
 
Join Date: Apr 2009
Location: burlington VT.
Bikes:
Posts: 2,472
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Quote:
Originally Posted by dabee1106 View Post
I forgot to say that this seat tube broke below the top tube by about 3 inches.+
whaaat?? never heard of that before, not from just riding, must have been a nasty crash caused a crack in the carbon and eventually it broke open.

I would say normally the seat tube between the top tube and BB take very little stress compared to the down tube and seatstays. If it was due to a crack then the frame did not fail, you did.
__________________
2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
1997 Trek ZX6000, 6061w/manitou spyder, xt/xtr, time atac
catonec is offline   Reply With Quote
Old 09-27-12, 04:24 AM   #6
speedy25
Senior Member
 
Join Date: Mar 2012
Location: NE oHIo
Bikes: Specialized, Trek, Diamondback, Schwinn, Peugeot
Posts: 630
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
And then there is a the problem facing us almost everyday in this modern world- Quality sucks! It may have broken just because it wasnt made right.Now that you have broken one, the chances of it happening again are next to nothing right? ( obscure refernce to: World according to Garp)-SP
speedy25 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 08:21 AM.