seat post failure analysis
07-29-20, 04:14 AM
#1
Senior Member
Thread Starter
seat post failure analysis
my riding style must be too harsh...bent the 35 cm steel post.
i only weight 140 pounds.
i only weight 140 pounds.
Last edited by mtb_addict; 07-29-20 at 04:51 AM.
07-29-20, 07:47 AM
#2
Junior Member
Cubewheels claim looks right. Also, the seat post looks rather long for this frame.
In the past, I’ve asked a metal fabricator to weld a 7/8” diameter (the size of the seat clamp) steel tube inside a 1” diameter one to build a (VERY) heavy, but tough, 450mm seat post. About 120mm of it was inside the frame, just for precaution.
I’m not using that anymore, but it held me at 345lb back then. Maybe that’s your solution.
In the past, I’ve asked a metal fabricator to weld a 7/8” diameter (the size of the seat clamp) steel tube inside a 1” diameter one to build a (VERY) heavy, but tough, 450mm seat post. About 120mm of it was inside the frame, just for precaution.
I’m not using that anymore, but it held me at 345lb back then. Maybe that’s your solution.
07-29-20, 08:26 AM
#3
Senior Member
Join Date: Jan 2009
Location: San Diego, CA
Posts: 3,661
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 836 Post(s)
Liked 1,058 Times
in
742 Posts
My guess is that it's just an inexpensive, weak seatpost. Not made to be extended that far out of the seat tube. Get any decent post with a clamp head for the seat on it and you should be OK. A few choices here for under $20. Measure how far the post you have extends from the frame clamp and add a minimum of 3"/75mm. Also make sure you know the correct diameter of the seatpost for your frame. https://www.google.com/search?ei=Y4U...sclient=psy-ab
Last edited by Crankycrank; 07-29-20 at 08:29 AM.
07-29-20, 08:44 AM
#4
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 14,949
Bikes: Tarmac Disc Comp Di2 - 2020
Mentioned: 51 Post(s)
Tagged: 0 Thread(s)
Quoted: 6176 Post(s)
Liked 4,794 Times
in
3,306 Posts
How much of the seat post is below the top of the seat tube?
Might be the picture angle, but it looks as if the top part of the seat post is a bigger diameter than the internal diameter of the seat tube. Was there something funky going on with that model seat post where it narrowed up at the bottom.
Might be the picture angle, but it looks as if the top part of the seat post is a bigger diameter than the internal diameter of the seat tube. Was there something funky going on with that model seat post where it narrowed up at the bottom.
07-29-20, 09:16 AM
#5
Banned
It's Mild steel , chosen for keeping cost low, bike cheap, not chrome-moly / 4130 that is stronger, but costs more..
07-29-20, 09:41 AM
#6
FLIR Kitten to 0.05C
Join Date: Sep 2014
Location: Lincoln, Nebraska
Posts: 5,331
Bikes: Roadie: Seven Axiom Race Ti w/Chorus 11s. CX/Adventure: Carver Gravel Grinder w/ Di2
Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 2349 Post(s)
Liked 406 Times
in
254 Posts
Cubewheels claim looks right. Also, the seat post looks rather long for this frame.
In the past, I’ve asked a metal fabricator to weld a 7/8” diameter (the size of the seat clamp) steel tube inside a 1” diameter one to build a (VERY) heavy, but tough, 450mm seat post. About 120mm of it was inside the frame, just for precaution.
I’m not using that anymore, but it held me at 345lb back then. Maybe that’s your solution.
In the past, I’ve asked a metal fabricator to weld a 7/8” diameter (the size of the seat clamp) steel tube inside a 1” diameter one to build a (VERY) heavy, but tough, 450mm seat post. About 120mm of it was inside the frame, just for precaution.
I’m not using that anymore, but it held me at 345lb back then. Maybe that’s your solution.
Also...the rusted Builder Bob bolt in place of a proper seatpost binder bolt is suspicious too...
07-29-20, 10:49 AM
#9
Senior Member
Join Date: Oct 2014
Location: Portland, OR
Posts: 12,890
Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder
Mentioned: 129 Post(s)
Tagged: 0 Thread(s)
Quoted: 4789 Post(s)
Liked 3,915 Times
in
2,546 Posts
Looks to me like a case of poor quality steel. I doubt the pinching at the back would have happened on a good post. I've never seen that and I've owned some funky bikes over the years.
Now that bend looks just like the bend my Hupel Rider post took (except yours is bent considerably more) when I hit a frost heave going >50 mph (80 kph) racing a mountain descent. Hupel Rider - a cheap post of soft aluminum. Replaced it with a Zeus post of much higher quality and had no more issue.
There are lots of steel posts like yours that are strong enough to have as much showing as yours and suffer all kinds of abuse. I've never heard of a Raleigh 3-speed post bending and some of those have seen epic abuse. If they bent, my dad would have passed on that story to me. He an d his buddies were some of those abusers. Measure up the diameter of your post and look for a new one.
Ben
Now that bend looks just like the bend my Hupel Rider post took (except yours is bent considerably more) when I hit a frost heave going >50 mph (80 kph) racing a mountain descent. Hupel Rider - a cheap post of soft aluminum. Replaced it with a Zeus post of much higher quality and had no more issue.
There are lots of steel posts like yours that are strong enough to have as much showing as yours and suffer all kinds of abuse. I've never heard of a Raleigh 3-speed post bending and some of those have seen epic abuse. If they bent, my dad would have passed on that story to me. He an d his buddies were some of those abusers. Measure up the diameter of your post and look for a new one.
Ben
07-31-20, 12:14 PM
#10
Senior Member
Thread Starter
the diameter is 25.4".
i noticed in reviews on Taobao that some little kiddie bikes very long seat post with 25.4.
so, this could explain it...this long seat post I got is actually for kids bikes...not designed to take the weight of an adult.
i noticed in reviews on Taobao that some little kiddie bikes very long seat post with 25.4.
so, this could explain it...this long seat post I got is actually for kids bikes...not designed to take the weight of an adult.
Last edited by mtb_addict; 07-31-20 at 12:24 PM.
07-31-20, 12:36 PM
#11
Banned
I bought a 1" ChroMoly seat post Imported thru Seattle Bike Supply under their Red Line BMX brand.
it worked fine with a foot extending out of the frame..
Wald is a purveyor of a similar diameter post but of mild steel..
it worked fine with a foot extending out of the frame..
Wald is a purveyor of a similar diameter post but of mild steel..
08-03-20, 12:20 PM
#14
Banned
what about "stainless steel"? & i assume aluminum 25.4 seat post is no good?
You have to be specific , as to alloys the ones like Kalloy are rather thick wall because its not a high strength alloy ..
6061- T 6 is stronger , so is adequate though the tube wall is thinner , so weighs less ..
some companies broach out the hole so tube wall thicker in alignment with the stresses applied. ..
likewise stainless steel what alloy in specific.. ?
Last edited by fietsbob; 08-03-20 at 12:24 PM.
08-04-20, 05:13 AM
#15
Senior Member
Join Date: Sep 2004
Location: Chicago area
Posts: 2,546
Bikes: Airborne "Carpe Diem", Motobecane "Mirage", Trek 6000, Strida 2, Dahon "Helios XL", Dahon "Mu XL", Tern "Verge S11i"
Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 980 Post(s)
Liked 580 Times
in
398 Posts
08-04-20, 07:05 AM
#16
Senior Member
Join Date: Feb 2012
Location: Rochester, NY
Posts: 18,056
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4194 Post(s)
Liked 3,837 Times
in
2,295 Posts
Do others see a bent seat tube, centered at the dropped "top tube"? It might be optical distortion from the camera but I've seen enough bent STs on ladies frames to not look for this too. This hinge point is why mixte frames are so much stiffer, their "top tubes" go past the ST and to the rear drop outs which move the compressive forces from a ST bending type to a drop out one. Andy
__________________
AndrewRStewart
AndrewRStewart
Likes For Andrew R Stewart:
08-04-20, 09:17 AM
#17
Banned
Top picture shows the buckling deformation of the type seen on the underside of top & down-tubes
On 'totaled' bikes suffering front end crash damage..
On 'totaled' bikes suffering front end crash damage..
08-04-20, 11:18 AM
#18
Senior Member
Join Date: Mar 2019
Posts: 1,606
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 581 Post(s)
Liked 921 Times
in
518 Posts
Probably caused by cheap steel seatpost, plus the clamp on the low-cost frame not being perfectly round.
THe other problem is that if you are resorting to an extra long seatpost, the frame is probably too small.
THe other problem is that if you are resorting to an extra long seatpost, the frame is probably too small.
08-08-20, 03:50 AM
#19
Senior Member
Thread Starter
08-08-20, 05:37 AM
#20
Senior Member
Join Date: May 2013
Location: Kips Bay, NY
Posts: 2,212
Bikes: Ritchey Swiss Cross | Teesdale Kona Hot | Haro Extreme | Specialized Stumpjumper Comp | Cannondale F1000 | Shogun 1000 | Cannondale M500 | Norco Charger | Marin Muirwoods 29er | Shogun Kaze | Breezer Lightning
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 576 Post(s)
Liked 1,001 Times
in
488 Posts
Many years ago I rode a vintage Schwinn 3sp frequently as a townie; I used to go into the vintage schwinn shop about 3 times a year to replace the bent seatpost.
08-08-20, 08:41 AM
#22
Disco Infiltrator
Join Date: May 2013
Location: Folsom CA
Posts: 13,446
Bikes: Stormchaser, Paramount, Tilt, Samba tandem
Mentioned: 72 Post(s)
Tagged: 0 Thread(s)
Quoted: 3126 Post(s)
Liked 2,102 Times
in
1,366 Posts
Just shear bad luck.
__________________
Genesis 49:16-17
Genesis 49:16-17
08-08-20, 09:14 AM
#23
Occam's Rotor
Join Date: Jul 2013
Posts: 7,248
Mentioned: 61 Post(s)
Tagged: 0 Thread(s)
Quoted: 2366 Post(s)
Liked 2,331 Times
in
1,164 Posts
Nice bike.
