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Discussion Starter · #1 ·
I'm OK, which is the main thing. Seriously, if I had not been riding on smooth concrete, this would have been a compete disaster. Added help was that I have a small Cannondale seatbag for a spare tube under my seat with small velcro loop that goes around the post in addition to the seat rails. That's the only thing that saved me from an aluminun colonoscopy. I have 5 Thomson seatposts and never had an issue with any of them till today. Across those posts I have over 100,000 care free miles. Owned this particular post 10 months and about 2000 miles. It's a Thomson Setback 31.6 410mm I have been using in Cannondale Caffeine framesets. The post has never been dropped, wrecked, knock over or even put in a repair stand.

Frankly I did not think this was possible because I read that the bolts are supposed to break before the seatpost. I have not even heard of a Thomson failure before.





 

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pedal pusher
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Wow, that sucks. Although, not everyone can brag about breaking a Thomson, so at least you have that much going for you.
 

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Discussion Starter · #7 ·
Jerk_Chicken said:
Ever hit a garage?
Nope. Don't even own a roof rack. Don't even own a garage.

Had to ride 18 miles home standing. That gets a little old after awhile. But not too bad. The weather was nice and I had the wind at my back.
 

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apacherider said:
Nope. Don't even own a roof rack. Don't even own a garage.

Had to ride 18 miles home standing. That gets a little old after awhile. But not too bad. The weather was nice and I had the wind at my back.
Wow, that is just nuts...looks like something absolutely catastrophic happened there. 18mi...no cell phone? I called the wife today to come and rescue me with the truck because I flatted on the road bike a 2nd time 15 miles from home, grrr.
 

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Is this even common for any kind of kind of seat post, including non name brands? Just thinking about the potential injury from taking that up the rear is disturbing.
 

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Any chance of getting a macro close up of the cross section on both ends? I'd love to see a close up of the damage.

I had a post fail on me on the trainer. But the funny part was that I was on the trainer b/c I had a broken collar bone so I couldn't use my arm/ride outside.

When the post broke, I collapsed to the floor banging my arm/shoulder into pretty much everything, that really hurt. But kinda funny now....:)
 

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Discussion Starter · #13 ·
civil said:
Any chance of getting a macro close up of the cross section on both ends? I'd love to see a close up of the damage.



That's about as good a photo as I can get with my crummy camera. I know nothing about metal or fatigue. The front side is the clean break side, the rear is the jagged side. From what I understand, the seatpost has an elliptical build to it with more material on the front/back rather than the sides. Does it look like the rear end lacks some material or is that just a result of the deforming when it broke?

In the photo below, see all the little teeny tiny fractures? They are on the rear facing side of the seat post. I don't know if they occured over time and I did not notice or if they occured as a result of the post at the moment it broke.

 

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Well, I'll make some generalizations here, but here's a quick guess..

Judging by the pic (I can't really tell b/c I can't see enough detail), it looks like a crack may have initiated here (arrow) and slowly propagated outward towards the line. Every loading cycle would cause the crack to propagate further. (front side of post in Tension and back side in Compression, cracks propagated through tension side due to opening and closing of crack from loading cycles)

The surface looks smooth up until the line, indicating the area that the fatigue crack propagated through.

To the right of the line, the remaining material wasn't strong enough to hold the stress and a shear failure (rough surface indicates this) occured, which would have deformed the rear end of the surface. The little wrinkles on the back of the post could be some straining due to the final shearing.

Do I'll chalk it up to a fatigue failure due to some stress riser/imperfection.

*edit* Glad you were OK ;)
 

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Geez that scares the crap out of me, and its a 31.6mm post too!

I guess I will be examining my 31.6mm straight post tonight real careful. From the lack of shiny rub points in the fracture zone it looks like it happened more or less all at once, sure looks thin on the relieved side.

Thanks for sharing with us, you may have saved someone elses rectum if they have a similar post issue. Glad you weren't hurt, it could have been real nasty.:eek:

Kinda makes me rethink the weight savings from these seat posts, for the small amount of weight a straight gauge tube sure sounds safer.
 

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Can't say I've seen a report of anything like the OP experienced FWIW. Everyone's gonna have a problem here and there. I think you can usually rely on Thomson's products more than many others in any case...
 

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RookieBeotch said:
Is this even common for any kind of kind of seat post, including non name brands? Just thinking about the potential injury from taking that up the rear is disturbing.
I've broken a post, and I don't think there is a huge danger of getting sodomized by the post. When it breaks you have the seat between your a$$ and the top of the post. Now, if you forget about it as you ride on, that's a different story.
 

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It's about showing up.
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Thompson will want to see this.

I'd send it to them for science alone. Now whether you want to see if they will cover it, that is another issue but I don't sense that you feel they are obliged
 

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Also looks to me like a MFR issue.
Just goes to show ALL parts need a regular check.

Oh, I would not have expected it to fail at that point. Should have been more flex further down the shaft. I would be very sure this was a fault from production.
 
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