BOLTING EAR FAILURE ON IMPACT
Despite all the reputation that Thomson has in making reliable cycling components and giving the best cushions against catastrophic failures on impact, this person's Elite seatpost (in particular, one of the bolting ears that stick out sideways ) broke off like chalk piece after a fall. The bike was leaned on a wall when it tipped over and fell sideways. Hence, the owner was apparently not even seated on the bike at the time of impact. The seatpost ear broke as he straightened the bike and it dropped in his hand. You can read some back and forth question/answers between me and the owner of the post as you scroll down. That will give some background information into the incident.
Compare this to Thomson's marketing literature online. Among several other things, the company happens to generously regard itself as producing the only seatpost in the market incorporating a "bending fuse" against catastrophic failure.
Their website says :
"The Thomson seatpost design incorporates a bending fuse to prevent catastrophic failure. All brand-x seatposts we tested - every one of them - failed in catastrophic failure with the seat and clamp components - and sometimes pieces of the tube and head - flying off in all directions. This type of failure would dump the rider."And something about impact absorbing clamps :
"Impact absorbing clamps - clamps, head, and assembly will spread and flex on impact to protect seat, rails, seatpost and rider. Easy on seats - allows seat to survive heavy impact loads without bending rails."
The owner of the seatpost, however, had a contrasting experience. He wrote on his blog after the incident :
"Forget the hype! Despite the claim that their seatposts are over "40% stronger" on ultimate strength test than the strongest production seatposts on the market, the Thomson Elite seatpost is not tough enough to withstand even a simple fall. And here's proof of that! This four-year-old post on my GT broke in the upper tube area, which is apparently 'strong enough to withstand 350 foot-lbs of torque', when the bike took a tumble sideways while it was stationary. It didn't "bend slightly" on impact like what the Thomson folks had you believe would happen but just crumbled like a cookie at the top. Actually, the OEM seatpost that I was using before I got the Thomson in a moment of weight-weenie lunacy seemed to take much harder knocks! And it looks like it could take plenty more! So, if you've got an Elite seatpost on your bike, watch out mate! It could be a disaster waiting to happen. "
I'm not sure what went wrong at Thomson's end to cause the seatpost to be brittle, but I'm just going to have to drop this one in the "Marketing Mishaps" section for now. This doesn't mean your Elite seatpost has the same problem. But it won't hurt to be informed. Out of 1000 apples, its likely that 2 end up being bad and that's the nature of manufacturing. When those bad apples that dont meet the standards turn into the customer's hands, that's where the issue reveals its uglier side. If Thomson stands by their word, they should delve into this incident and redress the issue (i.e If they are responsible. Corrosion, or user over tightening cannot be ruled out at this stage).
Take note that the lighter weight Masterpiece seatpost is essentially a machined out Elite. Also note that I suspect some of the brittleness MAY be caused due to anodizing, since the anodized Aluminum Oxide on the surface of the substrate is pretty brittle, even though hard. When the part elastically deforms, the oxide layers starts cracking and it propagates down into the substrate metal. This will only reduce the part's fatigue strength. [Source : Aluminum And Aluminum Alloys by J.R Davis & Associates (ASM)]
* * *
UPDATE March 19 12:00 pm
A CONVERSATION WITH THE USER OF THE SEAT POST
TO THE BLOGGER OF KHABAR BIKE (and user of the seat post) :
Due to the number of requests I'm getting to dig further into this issue, I have to put you in the spot light by flexing my Bee Muscles (crunnch). Please tell us the following if you don't mind :
1) Did you over tighten the seat clamp outside limiting values specified in the product sheet?
Khabar Bike : Not as far as I'm aware of. And it's been untouched since I last changed out the saddle about a year ago.
2) Did you wash the seat post a number of times without letting drying it out? Or have you used the bike a good number of times in the rain?
Khabar Bike : Definitely not. And I hate riding in the rain.
3) Is this the first time that the seatpost fell, taking a hit on the same area on the post in question?
Khabar Bike : Yes, as far as I can remember. And this is the first time I've ever had a broken seapost in the 12 years I've been a serious bike buff, with seven bikes including a lugged steel Pinarello, an old Trek bonded/carbon road bike and a 12-year-old Gary Fisher hardtail. They have a Syncros, ITM or OEM seatpost.
4) Did you buy the post from a recognized Thomson dealer? Brick and mortar shop? Online? Ebay? The possibility of a knock-off cannot be ruled out.
Khabar Bike : Yes. My LBS is one of the most reputable in the area. And the seatpost (paid about $70 for it) came with Thomson's unique but pretty useless bag and folded manual. I also have another Thomson seatpost (with layback), on my hardtail, which has been holding up fine for more than three years.
5) Pretty Useless Bag... the manual was in this useless bag. Did you read it?
Khabar Bike : Yes, I did and didn't find it useless at all.
6) Do you recall how the bike fell (orientation)?
Khabar Bike : It fell sideways. I picked it up by handlebar and the saddle and the back part broke off in my left hand.
7) Were you riding it when this happened (added weight) or did it free fall as it tipped over (just the bike weight)?
Khabar Bike : It was leaning against the wall when it tipped over.
8) Did the seatpost also have the saddle attached during that time?
Khabar Bike : Yes, the clamp was secure and undamaged, and still attached to the saddle.
Finally, I'd just like to say that I'm not as upset about the whole thing as I would've been a few years back when I was really into lightweight products. These days, anything that doesn't cost and arm and a leg and lasts is just fine with me.
Thank you.
* * *
THIS IS A WELL REGARDED SEAT POST AND MANY CONSIDER IT TO BE AMONG THE BEST DESIGNS.
KNOWN FACTS ARE GIVEN IN BLUE FONT. ANY EXTERNAL REFERENCES TO LINKS ARE IN RED.
This is the patent for the Thomson seatpost in question. The patent is titled "Lightweight High Strength Bicycle Seat Post And Associated Clamp Including Seat Angle Indicating Indicia". The main idea behind the intention was to provide a lightweight, strong seat post that has a wide range of adjustment and adequate cushion against catastophic failure.
The product is made from a 7000 series (Zn added) Al alloy and marketing materials claim that it is "40% stronger in ultimate strength tests, and has twice the fatigue life of 75 of the most strongest production seat posts on the market." The post also seems to have what is an obvious anodized black finish.
According to Thomson : "The head is not pressed or bonded in. This allows for superior strength and minimum weight, allowing higher strength at low weights."
One of the apparent design goals was to make this seat post able to withstand 350 in. lbs of torque, with bending taking place at 250 in. lbs of torque. There appears to be shoulder fillet at the tube-head interface (machined). The bigger the fillet radius, the more the stress concentration factor is reduced. Thomson designers should have selected the fillet radius for a desired stress concentration factor for this shaft for the particular loading case (torsion, tension, bending etc). The critical numbers here are the D/d ratio and the r/d ratio which can be referenced to known and published charts to find the stress concentration factor (you can work backwards in design as well). See Peterson's Stress Concentration Factors by Walter Pilkey for more information.
When you first feel the seatpost in your hand, you'll come across the sharp features at the sides of the head. At the edges as shown, chamfer radii appear to be very small, hardly noticeable. See picture below.
This isn't a circular cross-section, as you can see. Thomson says : "Natural ellipse bore inside tube for optimum strength to weight ratio." The thickness is higher on the front and rear end of the seat post, corresponding with the directions of the bolt locations on the head above it.
Moment of Inertia (or Second Moment of Area) of a hollow elliptical section beam about a horizontal axis passing through the center of gravity. Practically, it is the measure of the capacity of a cross-section to resist bending. See The Design Of Structures By Samuel Anglin, C.E
The same for a circular hollow cross section
If you look carefully to the tube body section under the light close to the logo, you'll see some fine marks/grooves that extends throughout the length of the tube. Is this a deliberate feature to prevent slippage of the post when clamped at the seat tube? Its pretty nice.
Here's the top and bottom clamp together with the swivel nuts inside. This arrangement on the tube supposedly allows the claim : "Infinite tilt adjustment minus 5° and plus 29°."
The product sheet says : "All Thomson seatposts are designed with positive metal to metal stops. These positive stops and bolt lengths are designed to work together to allow a maximum 5 upto 29 degree down tilt. This means the tilt adjustment of the clamps will be stopped by the positive stop before the back bolt runs out of the nut. This prevents damage to bolts, nuts, ears, and clamps that may otherwise occur with over adjustment."
On the product sheet, Thomson mentions very clearly : "Never tighten the front bolt hard against the positive stop. Make sure that bolts are tightened against each other. Always tighten the back bolt to 60 inch lbs of torque. If the front bolt is tightened hard against the front ear, the force created by that tightening will be subtracted from the bolt's available force to withstand high impact loads. If the front bolt is tightened hard against the stop and not against the rear bolt, the rear bolt could loosen during the impact loads."
Recommended torque values have been set in the product sheet to 60 inch lbs for each bolt.
A warning in the product sheet cautioning that if the clamp lip touches the tube, the seatpost could dimple during clamp tightening.
Another warning that post is for use with 7mm seatrails only.
Thomson says : "The Thomson seatpost design incorporates a bending fuse to prevent catastrophic failure. All brand-x seatposts we tested - every one of them - failed in catastrophic failure with the seat and clamp components - and sometimes pieces of the tube and head - flying off in all directions. This type of failure would dump the ride."
Finally, the highlight of the Thomson marketing is this statement :
What remains to be researched is how the bike with the seat post and saddle fell, validate the claims of the user (see above) when he replied that he did not overtighten any of the two bolts, validate the claims of the presence of a bending fuse and the actual strength of the product from the manufacturer, do a small paper and pencil analysis of the forces and stresses encountered and compare this with known the known design limits of the seat post.
The owner has made it known to us that for about a year, he did not have to change the saddle on the seat post. It is likely that during this time, he may have lost notice of the critical areas of the seat post. A stress riser may have led to the formation and propogation of a tiny crack, which, upon the post striking the ground in this fall, led to the severing of one of the bolting spots from the tube due to the torsional shear stresses encountered.
What was nice from writing this post so far has been the fact that this issue has been exposed to the world. Users must remain careful of how they install and use cycling products. At the same time, competition in the cycling industry is cutthroat. Over the years, we've seen an increasing number of bad designs with bold marketing claims and promises. Few have stood the test of time.
A reader notified me of another Thomson seatpost failure incident, only this time it was a setback post and the failure occurred on the post body itself, very close the bolting ears. These pictures were shown on Mtbr.com Forums, by user Apacherider. Incidents like these are not safe and opens up a range of possibilities for injury. Since the above incident and this new one is not very far apart in occurence date, Thomson must really dig into the backgrounds of the causes. It seems to me as if these posts are in need of more reinforcing in the areas around the bolting ears, including the ears themselves.
UPDATE March 25
DESIGN FEATURES OF THOMSON ELITE SEATPOST.
DESIGN FEATURES OF THOMSON ELITE SEATPOST.
THIS IS A WELL REGARDED SEAT POST AND MANY CONSIDER IT TO BE AMONG THE BEST DESIGNS.
KNOWN FACTS ARE GIVEN IN BLUE FONT. ANY EXTERNAL REFERENCES TO LINKS ARE IN RED.
This is the patent for the Thomson seatpost in question. The patent is titled "Lightweight High Strength Bicycle Seat Post And Associated Clamp Including Seat Angle Indicating Indicia". The main idea behind the intention was to provide a lightweight, strong seat post that has a wide range of adjustment and adequate cushion against catastophic failure.
The product is made from a 7000 series (Zn added) Al alloy and marketing materials claim that it is "40% stronger in ultimate strength tests, and has twice the fatigue life of 75 of the most strongest production seat posts on the market." The post also seems to have what is an obvious anodized black finish.
According to Thomson : "The head is not pressed or bonded in. This allows for superior strength and minimum weight, allowing higher strength at low weights." 
One of the apparent design goals was to make this seat post able to withstand 350 in. lbs of torque, with bending taking place at 250 in. lbs of torque. There appears to be shoulder fillet at the tube-head interface (machined). The bigger the fillet radius, the more the stress concentration factor is reduced. Thomson designers should have selected the fillet radius for a desired stress concentration factor for this shaft for the particular loading case (torsion, tension, bending etc). The critical numbers here are the D/d ratio and the r/d ratio which can be referenced to known and published charts to find the stress concentration factor (you can work backwards in design as well). See Peterson's Stress Concentration Factors by Walter Pilkey for more information.
When you first feel the seatpost in your hand, you'll come across the sharp features at the sides of the head. At the edges as shown, chamfer radii appear to be very small, hardly noticeable. See picture below.
This isn't a circular cross-section, as you can see. Thomson says : "Natural ellipse bore inside tube for optimum strength to weight ratio." The thickness is higher on the front and rear end of the seat post, corresponding with the directions of the bolt locations on the head above it.
Moment of Inertia (or Second Moment of Area) of a hollow elliptical section beam about a horizontal axis passing through the center of gravity. Practically, it is the measure of the capacity of a cross-section to resist bending. See The Design Of Structures By Samuel Anglin, C.E
The same for a circular hollow cross section
If you look carefully to the tube body section under the light close to the logo, you'll see some fine marks/grooves that extends throughout the length of the tube. Is this a deliberate feature to prevent slippage of the post when clamped at the seat tube? Its pretty nice.
Here's the top and bottom clamp together with the swivel nuts inside. This arrangement on the tube supposedly allows the claim : "Infinite tilt adjustment minus 5° and plus 29°."
The product sheet says : "All Thomson seatposts are designed with positive metal to metal stops. These positive stops and bolt lengths are designed to work together to allow a maximum 5 upto 29 degree down tilt. This means the tilt adjustment of the clamps will be stopped by the positive stop before the back bolt runs out of the nut. This prevents damage to bolts, nuts, ears, and clamps that may otherwise occur with over adjustment."
On the product sheet, Thomson mentions very clearly : "Never tighten the front bolt hard against the positive stop. Make sure that bolts are tightened against each other. Always tighten the back bolt to 60 inch lbs of torque. If the front bolt is tightened hard against the front ear, the force created by that tightening will be subtracted from the bolt's available force to withstand high impact loads. If the front bolt is tightened hard against the stop and not against the rear bolt, the rear bolt could loosen during the impact loads." 
Recommended torque values have been set in the product sheet to 60 inch lbs for each bolt.
A warning in the product sheet cautioning that if the clamp lip touches the tube, the seatpost could dimple during clamp tightening.
Another warning that post is for use with 7mm seatrails only.
Thomson says : "The Thomson seatpost design incorporates a bending fuse to prevent catastrophic failure. All brand-x seatposts we tested - every one of them - failed in catastrophic failure with the seat and clamp components - and sometimes pieces of the tube and head - flying off in all directions. This type of failure would dump the ride." What stumps me is that for all that marketing on their website, there is actually no bending fuse description on the instruction sheet. I'd actually like to see a description of this and how it works. Is this incorporated into the top and bottom clamp design somehow, and not mentioned? What say, Thomson?
Finally, the highlight of the Thomson marketing is this statement :
"The Thomson seatpost has a clamp, head, and upper tube strong enough to withstand 350 foot-lbs of torque. The tube will start to yield and bend at the seat tube clamp at about 250 foot-lbs of torque. Remember all brand-x posts we tested flew apart at less than 150 foot-lbs of torque. Under severe impact the Thomson seatpost would bend slightly and allows the rider to come to a safe stop or finish the ride. The ride could continue."
My thoughts on this statement are that putting this alongside with what was actually observed by the user who broke his seat post (see top picture of failure), the tube did not withstand the force and there was no observation of bending. It appears that the impact forces approached ultimate strength for the broken area in question and broke catastrophically. It looks like the rider was not injured in any serious fashion.What remains to be researched is how the bike with the seat post and saddle fell, validate the claims of the user (see above) when he replied that he did not overtighten any of the two bolts, validate the claims of the presence of a bending fuse and the actual strength of the product from the manufacturer, do a small paper and pencil analysis of the forces and stresses encountered and compare this with known the known design limits of the seat post.
The owner has made it known to us that for about a year, he did not have to change the saddle on the seat post. It is likely that during this time, he may have lost notice of the critical areas of the seat post. A stress riser may have led to the formation and propogation of a tiny crack, which, upon the post striking the ground in this fall, led to the severing of one of the bolting spots from the tube due to the torsional shear stresses encountered.
What was nice from writing this post so far has been the fact that this issue has been exposed to the world. Users must remain careful of how they install and use cycling products. At the same time, competition in the cycling industry is cutthroat. Over the years, we've seen an increasing number of bad designs with bold marketing claims and promises. Few have stood the test of time.
UPDATE APRIL 12, 2009
A reader notified me of another Thomson seatpost failure incident, only this time it was a setback post and the failure occurred on the post body itself, very close the bolting ears. These pictures were shown on Mtbr.com Forums, by user Apacherider. Incidents like these are not safe and opens up a range of possibilities for injury. Since the above incident and this new one is not very far apart in occurence date, Thomson must really dig into the backgrounds of the causes. It seems to me as if these posts are in need of more reinforcing in the areas around the bolting ears, including the ears themselves.
* * *
Posts
Did he follow up with Thomson? What did they have to say about it?
ReplyDeleteAlso, as the owner of some components that I have seen counterfeited (like Zipp), you can't rule that out. Are we all 100% sure that this post was genuine and passed factory spec?
I expect to hear follow-up about this one, I'm very surprised.
what on earth is a bending fuse. sounds like a cousin of electrical fuse. to think all that's under my bottom....
ReplyDeleteThat is a funny looking fracture path. I wonder if after four years and a little corrosion, that a stress riser had formed and the shock of the fall caused the failure?
ReplyDeleteI see a lot of corrosion in places that have air pollution. For instance, I see much more in Dallas than in San Antonio.
Thanks for your great posts!
I'd be careful making too many assumptions about what happened and why until such time as all of the facts were gathered. While it's possible that the post may have had a manufacturing defect or simply failed as purported, what's not addressed are things such as how much torque was applied to the seat clamp bolts: it's only 60 in lbs for the Elite and a mere 45 in lbs for the Masterpiece. Just looking at the break, and lacking other reports of similar failures, I'd be more inclined to suspect the torque spec for a seat clamp bolt was exceeded.
ReplyDeleteWhen I saw your reference to a failure rate of 2 in 1,000, I think of the doctor telling his patient that this particular operation has a mortality rate of 1% and is very safe.
ReplyDelete"That's fine, but if you are the 1%, you are 100% dead."
Could it have been over tightened? That would be my guess.
ReplyDeleteGuys,
ReplyDeleteI put an update on this post asking the user to follow up on how he installed it and in what conditions he used the product.
ron : it would be nice to have a closeup pic of the fracture site as well.
ReplyDeleteAnon : I can't produce that picture because this seat post is not mine. We'll see if any more updates follow.
ReplyDeleteInterestingly, I checked the personal reviews of this seatpost on MTB Review.
Among several good reviews, there were a bunch of those who experienced creaking sounds, slippages, broken clamp screws and crimping.
The bike fell, end of story for any high $ weight weenie component. You hit it just right it will break. How long do we expect this thing to last anyways? Or what abuse should it be made to suffer?
ReplyDeleteSteven : Thanks for your comment. But its not an intelligent comment. Far too often, replies such as yours have been the defacto response from observers of other people's plight. This isn't about making something to last your life. This is about the fashion in which it fell, and the promises of the company in terms of the torque and fatigue loads it can expect to withstand. Nowhere does Thomson make a comment that their seatposts are strictly made for 4 years. "Sorry buddy, after that whatever happens to your beloved items is not our fault". I don't feel this is the way Thomson thinks.
ReplyDeleteSeems like there could be a stress riser in that area just by the shape of the machining of the clamp area. A tiny flaw could start a crack which would spread quickly. There's just not a lot of metal there.
ReplyDeleteI used to run Avocet seatposts in the early 1980s. They used two thin clamp bolts from below. Periodically the head would pop off of one of them. It happened in a race once. I finished the course with the saddle all afloat. The uneven strain caused by continuing to ride with a broken bolt started a crack in the head of the post itself.
The rider is the heaviest part of the bike. The seat post is one of the smaller parts. It's surprising there aren't more failures.
Thanks for taking up this issue in your blog. Didn't really expect anyone other than the Thomson folks to notice it. And sorry about the shabby Vox comments section. As for your questions:
ReplyDelete1) Did you over tighten the seat clamp outside limiting values specified in the product sheet?
Not as far as I'm aware of. And it's been untouched since I last changed out the saddle about a year.
2) Did you wash the seat post a number of times without letting drying it out? Or have you used the bike a good number of times in the rain?
Definitely not. And I hate riding in the rain.
3) Is this the first time that the seatpost fell, taking a hit on the same area on the post in question?
Yes, as far as I can remember. And this is the first time I've ever had a broken seapost in the 12 years I've been a serious bike buff, with seven bikes including a lugged steel Pinarello, an old Trek bonded/carbon road bike and a 12-year-old Gary Fisher hardtail. They have a Syncros, ITM or OEM seatpost.
4) Did you buy the post from a recognized Thomson dealer? Brick and mortar shop? Online? Ebay? The possibility of a knock-off cannot be ruled out.
Yes. My LBS is one of the most reputable in the area. And the seatpost (paid about $70 for it) came with Thomson's unique but pretty useless bag and folded manual. I also have another Thomson seatpost (with layback), on my hardtail, which has been holding up fine for more than three years.
Finally, I'd just like to say that I'm not as upset about the whole thing as I would've been a few years back when I was really into lightweight products. These days, anything that doesn't cost and arm and a leg and lasts is just fine with me.
KHABAR BIKE
Archtop :
ReplyDeleteThanks for the replies. I appreciate it.
Evaluating your responses, my feeling is that this could be an issue originating in the upstream manufacturing phase from Thomson. I won't say this is a poor design, and it seems like more people have said good things about this seatpost than any other that I can possibly think of. Now whether the design of the Elite has changed over the last 4-5 years, I do not know. Certainly competition makes you do some risky things. That risk may be involved in changing the shape and dimensions of the design, which may add secondary problems that may be overlooked such as...well, a stress riser.
What do others think from his response?
my feeling is that the failure was caused due to a number of problems as opposed to one. it all comes down like a deck of cards. in this instance it seems to be a defect, but then what you do with the product down the line adds injury after injury and finally, the darn thing just gives up.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteP.S. An alloy nipple on a five-year-old self-built rear wheel failed while I was riding my single-speed yesterday. Luckily, the wheel remained true enough for me to ride back home (5km). Another lesson learned: No more aluminium nipples!
ReplyDeleteKHABAR BIKE
[i][b]1) Did you over tighten the seat clamp outside limiting values specified in the product sheet?[/b]
ReplyDeleteNot as far as I'm aware of.
[b]What do others think from his response?[/b][/i]
IMHO, over torque remains high on my list of contributing, if not root cause. Relative torque is just not a safe bet on any lighter weight alloy, alum or carbon components. The fall and impact was likely the coup de grace on a pre-existing condition (preloading the seat post mast well beyond spec) much the same way carbon handlebars and seat posts that are over torqued and damaged during installation will eventually fail a result from debonds in the crush zone.
If returned to Thomson (or taken to another precision machined parts manufacturer with full QA / NDI assets and MEs on staff) I'm sure they would be more than happy to conduct an objective fracture analysis that would remove all doubt as to nature of the break.
IMHO, over torque remains high on my list of contributing, if not root cause. Relative torque is just not a safe bet on any lighter weight alloy, alum or carbon components. The fall and impact was likely the coup de grace on a pre-existing condition (preloading the seat post mast well beyond spec) much the same way carbon handlebars and seat posts that are over torqued and damaged during installation will eventually fail a result from debonds in the crush zone.
ReplyDeleteWhile I won't discount it as a remote possibility, I'm pretty sure that I didn't overtighten the bolts. Yes, a torque wrench would have helped, but as someone who's been using and frequently swopping out thin-walled, two-bolt seatposts and carbon handlebars between bikes for more than a decade, I'm quite clued-in on the dangers of over-torque.
I did end up with a stripped bolt (replaced by the manufacturer for free) once... when I first installed a saddle on my 12-year-old Syncros Hardcore (still going strong on an old Trek 2100 after years of solid service on a first-generation Gary Fisher Genesis Big Sur), but since then I've been extra careful about avoiding overtightening.
Also, I'd like to point out that the bolts of the Thomson post in question had remained untouched for months since I changed out the saddle, and I've ridden the bike (mostly 10 to 15km offoad rides) at least twice a week since then.
Actually, I'm just glad that the post didn't fail while I was out riding. That would have been a really "sore/sorry ass" situation!
But the main point here is, this incident has shattered my confidence in Thomson seatposts, and now I'm worried that the second one I have might fail in a similar fashion.
This is frustrating and ridiculous!
ReplyDeleteNone of us knows why this failed, yet some seem as if you feel betrayed that it did fail. Bike parts do not last forever, and frankly, I could care less if you or anyone else thinks this is an unintelligent response. I think it is over-the-top unintelligent to act as if Thomson committed some offense because this post broke when you have limited photographs, hearsay, conjecture, and nothing else to demonstrate that it was not abuse, neglect, or inadequate installation.
Even with a very limited amount of first hand information, we still are unsure if it was secured properly. Let's not rule out the possibility that this was UNDER-torqued or over-torqued. I do not care how many bikes a guy owns, or how many bolts he has tightened, his hands are not calibrated, and any claims that he can accurately and precisely reproduce the proper torque without adequate tools (used properly) is utter comedy!
If we post up for the world to see every time a part breaks from "JRA" and act as if the manufacturer is likely to blame, you are going to need a lot more bandwidth. I have heard a lot of JRA BS over the years...pardon me for remaining skeptical.
Overtightening, overtightening, overtightening. If the owner is legit, have him send the seatpost to Thomson and the great staff there will check it out, determine what the problem is. They will sort him out as well. Thomson has been great to me and I own a pair of Thomson masterpieces myself and an X2 and X4 Elite stem.
ReplyDeleteLast 2 comments are SPOT ON !!
ReplyDeleteSuper, over high expectations always end in disappointment - or a destructive 'blame-game'.
Ron, is everything you do 100% squeaky perfect ? - if so then fine. Otherwise follow the advice in the last 2 posts.
The Profile Racing BMX freestyle and race teams have been using Thomson seatposts on their bikes for years, and I guarantee that each of those seatposts have been involved in multiple impacts as severe as any you could imagine, particularly the freestyle team, and to my knowledge not one has ever broken.
ReplyDeleteI'm not saying it's impossible, but it's highly unlikely that the person with the broken seatpost has told us the whole story. If I had to guess I'd say overtightening as well.
Wow! Didn't expect to be stomped on by the "proper-use police". I'm also amused how this thread is turning into a sort of "manufacturer's right, user's wrong" argument. Anyway, more photos here if anybody still cares. Interestingly, just stumbled onto the bicycle component failure section of this materials engineering site.
ReplyDeleteWhoa! How is it that "Anonymous" posters are always so vocal/rude? I'm just interested to try and find out what caused the seat post to fail and ranting about over tightening or putting words in peoples mouths about how they're blaming manufacturers isn't going to enlighten anyone.
ReplyDeleteI'd love to see more close up pics, does your camera have a macro function Archtop?
I'll put some closeup pictures of an elite post. Not broken. Thanks.
ReplyDeleteI did not definitely pass the blame onto Thomson. I know that for years, this post has been making the best reviews. But given the user's 10 year experience with proper usage of components and some of his replies to my questions, you cannot tell him that he's wrong either.
The issue now is to get this straight, and have some feedback material for Thomson, just for future reference in their design and manufacturing work.
Why are people headbutting the owner of the seat post? Do you need a 100 dollar torque wrench to calibrate a seatpost clamp? Really? With carbon, you can't afford to be careless really. But you can wing it with aluminum, assuming you're not out of your mind to give it 15 turns past its max limit. I don't think this is an over tightening issue at all.
ReplyDeleteNo you do not need a 100 dollar torque wrench. A good torque wrench can be had for much less. Perhaps you do not need a torque wrench at all.
ReplyDeleteOTOH if you want to start your posts with "Forget the hype!"
or call it a "marketing mishap", you might want to make sure you did everything correctly before you try and cry to the masses and stick the turd in someone else's pocket.
The hype is right there on the OP's Blog. It should have said, "I broke a bike part, I am not sure how, but I sure hope the un-named manufacturer will handle things properly." Then report back later with results.
Nope! Instead a bunch of hype was created and then surrounded by a bunch of BS. Until someone with real credentials has a look at this thing, I see no other appropriate reaction other than to think this person is trying to force a manufacturers hand by trying to air some laundry that may not even be dirty.
Thomson's reputation speaks for itself. If you think it is wrong for me to side with them...Tough. Thomson has demonstrated years of great customer service, and good design. This thread and the Blog of the OP has not demonstrated anything that makes me question Thomson's reputation.
Anon at 9:14 : Do you have to doubt the reputation of Thomson through this post? Absolutely not. You believe in them, and thats good. But that may not be exactly the feeling of another user who, because of a prematurely broken component, succumbs to a huge medical bill post injury.
ReplyDeleteUnder strict liability, the manufacturer is liable if the product is defective (or breach of warranty), even if the manufacturer was not negligent in making that product defective. I'm sure as a manufacturer, Thomson will be knowledgeable of this law and will take such cases with stride. If this is a design defect, it will come to light pretty soon. If it doesn't, something in the original story was wrong. Yes, I don't refute that.
Yes Ron, but *was* anyone hurt? Or is this yet another attempt at sensationalism?
ReplyDeleteThis entire matter is going from bad to worse now that you are bringing up liability. I am not sure of your qualifications, but mine certainly do not allow for solid engineering or legal conclusions to be made from the information presented.
Sorry, my bad. It is your site, do what you like. I will leave this matter to you, the OP, and Thomson. The situation certainly does not require any more un-informed opinions.
@ Anon 11:52 - Good engineering practice does not 'wait' for accidents to happen. Call it sensationalism or not, but we all know that injuries in cycling are nothing short of troublesome. If sensationalism can get people more aware of the possibility of mishaps when such and such incident occurred, then its a service.
ReplyDeleteDo you need a 100 dollar torque wrench to calibrate a seatpost clamp?
ReplyDeleteA high-quality beam-type torque wrench is about $30-$35. Of course, once you have the torque wrench you'd need to find the torque specs for a given component and that too takes a certain level of discipline and attention to detail.
Really? I don't think this is an over tightening issue at all.
Based on which of the very few facts that have been presented here? Or, is it simply the truthiness of the whole situation as someone who has emphathy for khabar bike?
Seriously, slippery slope and red herring arguments or empathy are not substitutes for facts which are still in short supply given the tenor of the original posting.
Mark :
ReplyDeleteYou're making a big cry for truthiness and fact.
I wonder what is fact to you? Please explain the information you would acquire to make the best judgement about this case.
Given the geographical location of the user, its a little challenging to actually inspect it. Many had asked the blogger of Khabar bike for a closeup picture of the fatigued parts but we got none. I understand that the post may have been sent to Thomson already. As to how Thomson exactly manufacturers this post is a black box. Good luck finding proprietery information! All we know is that the post and head have been machined from one piece.
I did make the extra effort to use this blog to pose the user some direct questions as to the history of the seat post.
You need to scroll up and read the owner's replies for my questions once again. He has claimed that he did not touch the seatpost clamp for about a year since he last changed his saddle out. Among other things, the seatpost has not fallen before this incident and he also has not ridden in wet weather. Whether this man is fooling us or not is another topic for another day. This is a long time bike rider and bike blogger and I doubt that he has the time to mislead the public and make a fairy tale out of his bad experience like you feel. I'm not saying that the internet is not filled with that kind of nonsense, but I choose my stories carefully.
Meanwhile, absolute fact and transparency will be in short supply to us...unless you're willing to help and fill that gap. During this time, people can make judgements and bring their experience to light in this matter in order to discuss what may have gone wrong with the product. I don't see anything wrong with that.
You're making a big cry for truthiness and fact.
ReplyDeleteFacts, not truthiness. Truthiness is hearing what you want to hear to support what you'd like to be true.
I wonder what is fact to you? Please explain the information you would acquire to make the best judgement about this case.
The results of a fracture analysis by the manufacturer or a qualified 3rd party lab, plain and simple.
I've had more than my fair share of failed parts and in each case the photos and parts were sent back to the manufacturer for proper analysis and remedy. In cases where it was a potential safety issue vs. life/durability concern I have in the past shared what others with similar equipment should look for, without rendering judgment as to cause or remedy based on incomplete information. We do the same thing in aerospace when a failed part or an aircraft is brought to our attention; it's SOP.
Only after the facts and root cause analysis is complete can you then make informed statements about root cause, contributing factors, responsibility and appropriate corrective / compensatory measures.
In this case there was an immediate rush to judgment and that is simply not prudent or appropriate based on that facts that as presented.
The results of a fracture analysis by the manufacturer or a qualified 3rd party lab, plain and simple.
ReplyDeleteDo you think each of us will be given the results of fracture analysis? It sounds good on paper. This information is not easy to attain.
We did not make any promises to get to the root cause of this problem here, using nothing but hearsay. We're taking a dab at the issue. Like I said for the umpteenth time, this open forum here allows for that.
Do you think each of us will be given the results of fracture analysis?
ReplyDeleteShort of having a serious accident where a settlement was reached that included the execution of a non-disclosure agreement by the aggrieved party, most folks are free to pass along what they learn when a failed part is returned for warranty or failure analysis. It there was a material defect or quality escape the part may simply be replaced at no cost or, in the case of an older failed part, at manufacturers wholesale without much fanfare as a good will gesture. If there is a widespread problem where an entire production lot was bad, word will get around quickly as others will invariably report similar if not nearly identical failures, such is the nature of these things. If the customer simply ‘screwed the pooch’ they’ll usually be pretty up front about that too (not that the customer will necessarily be forthcoming with a mea culpa) and may still offer a good will replacement. In any event, how the manufacturer deals with these types of issues says a lot about the company an its products and in this case Thomson was pronounced guilty at the outset which is where I take issue; again, from the root
Despite all the reputation that Thomson has in making reliable cycling components, this person's Elite seatpost (popular) broke off at the tip like a chalk piece after a fall… I'm not sure what went wrong at Thomson's end to cause the seatpost to be brittle, but I'm just going to have to drop this one in the "Marketing Mishaps" section for now.
We did not make any promises to get to the root cause of this problem here, using nothing but hearsay. We're taking a dab at the issue. Like I said for the umpteenth time, this open forum here allows for that.
All of these things sound reasonable; however, at least in this example (remembering my admonishment in the Calfee thread that I am a new reader) your original commentary biased readers by starting off with:
Despite all the reputation that Thomson has in making reliable cycling components, this person's Elite seatpost (popular) broke off at the tip like a chalk piece after a fall…
And then went on to pass judgment and poison the well with:
I'm not sure what went wrong at Thomson's end to cause the seatpost to be brittle, but I'm just going to have to drop this one in the "Marketing Mishaps" section for now.
These are not writing techniques that invite open dialog they are, instead, polarizing statements. If the objective is to create a lively debate without passing judgment then by all means do so, but do it in a way that makes it clear, e.g., “While we can’t no for certain what happened here based on what has been presented thus far, what similar experiences have readers had that might suggest what may have happened?” That’s a far cry from the statements that were offered.
Thank you for reading. I'm an opinionated writer which I will agree with. Please feel free to go elsewhere to find absolutely unbiased information for reading material. You'll be hard pressed to find something close, especially in a blog. You have chosen to read the blog agreeing to find such judgemental nuances from time to time. Sometimes always.
ReplyDeleteI'm an Thomson elite user myself. That is one of the two seatposts I own, for about 2 years now. However, I'm not going to be partial to them because of what I experience.
Archtop Soul : Can you get us a closeup picture of the failure site? I take it that you're pretty good with your camera.
ReplyDeleteOthers : I tried to be proactive and ask Thomson about how they plan on arriving to the root cause of this issue. Surprisingly, their email address is dysfunctional.
ReplyDelete"We're sorry. There's a problem with the e-mail address(es) you're trying to send to. Please verify the address(es) and try again. If you continue to have problems, please contact Customer Support at (480) 624-2500."
So much for customer service. Anyone else experience the same issue? Maybe temporary?
Just tried myself. Same issue. Their inbox is probably swamped.
ReplyDeleteBB : I doubt that. If that's the case, they would have received a warning that their email is nearing the quota limit.
ReplyDeleteWhat stumps me is that for all that marketing on their website, there is actually no bending fuse description on the instruction sheet. I'd actually like to see a description of this and how it works. Is this incorporated into the top and bottom clamp design somehow, and not mentioned?
ReplyDeleteBending fuse refers to the failure mode of a Thomson seat post shaft vs. fracture / shearing-off. You can find it mentioned in their FAQs on carbon seat posts: http://www.lhthomson.com/carbon_seatpost.htm
We designed the Thomson post to bend above the max line, bend-not break. We designed all of the clamping mechanism to be stronger than the post so that no matter what, the saddle stays with the post in a failure. We received a patent for this failure mode; we call it our bending fuse.
For a more technical description you can refer to the actual patent:
http://www.google.com/patents?vid=USPAT5664829
The bending fuse failure mode is illustrated at Figure 11 on Page 5 and described in detail beginning midway through column 7 and continuing onto column 8.
Regarding email address snafu - judging from the passion in responses and probable viral spread of this issue, it is not unlikely that the email inbox has overflowed often, and has been disabled
ReplyDeleteI own a Masterpiece and an Elite seatpost, and a 73 deg stem. All doing quite well.
I had a Kalloy seatpost break at the clamp. There was a small burr that scored the seatpost. I assume that initiated the problem that repeated stress over time finished the job. Point is that Kalloy posts are simple, overbuilt, heavy sticks of aluminum. So if anybody is thinking of abandoning Thomson posts for a heavy stick of aluminum they should be aware that cheap and heavy stuff breaks too.
I appreciate this blog's analysis of engineering vs marketing vs field reports. I appreciate the opinions too whether I agree or not. The ball belongs to Thomson now. I'd like to see the blog author take up a discussion with Thomson and 99.99% of the others of us not get involved directly with the mfr.
I offer this comparison. Think of an airplane mfr. Have their products failed catastrophically? Have those failures prevented you from flying? It's all about the percentages. This incident doesn't strike me as a marketing fail. I guess all marketing blather is doomed to failure by some measure. I ignore the stuff unless it's annoying or funny. I bought Thomson products based on user reviews on the web and technical specs from the mfr.
Just started reading this blog. Very nice. Thanks for the effort.
60 inch pounds = 5 foot pounds = NOT VERY MUCH PRESSURE.
ReplyDeleteWithout a torque wrench it would be very hard to know if it was overtightened.
A proper metalurgical analysis would reveal the failure mechanism.
Mark,
ReplyDeleteThanks for the info. However, its very limited in explanation. The website link has nothing technical about the bending fuse. There's two instances of bending fuse mentioned in the patent 5,664,829 (pages 9 and 11 as per search) that is also very limited in explanation in what it is exactly from a materials and design standpoint, save for the fact that they mention its purpose is to prevent catastrophic failure.
What do I think of the bending fuse? Thomson designers were aware of fatigue limitation of aluminum and added in an extra factor of safety (or overbuilt it) to cushion against catastrophic failure. They use a special term for this called "bending fuse". In my opinion, I see this bending fuse idea as nothing more than that extra safety factor, which is nothing new and has been known in engineering since the Byzantine empire. To say that this idea is not used by other seat post manufacturers (or prior art) is...well, is that really true?
If you have any more explanations to make the bending fuse a legit innovative idea, let me know. But for now, I feel the term is misleading in that I thought it was a separate component on the seatpost.
For further reference to bending fuse being nothing more than factor of safety :
ReplyDeleteElite seatposts are 40% stronger in ultimate strength tests, and have twice the fatigue life of the 75 strongest production seatposts on the market. Further, all Thomson posts are designed with a bending fuse so they bend slightly at their failure point, rather than snap completely, to allow for a safe failure.
Link : http://www.lhthomson.com/docs/LHT_2005_products.pdf
In my opinion, I see this bending fuse idea as nothing more than that extra safety factor, which is nothing new and has been known in engineering since the Byzantine empire. To say that this idea is not used by other seat post manufacturers (or prior art) is...well, is that really true?
ReplyDeleteRon - Maybe they meant that similar lightweight (weightweenie) posts in the market favor lightweight over strength and factor of safety. I'll be hard pressed to believe that commonly used, mainstream AL seatposts don't take factors of safety into account.
Ron wrote If you have any more explanations to make the bending fuse a legit innovative idea, let me know. But for now, I feel the term is misleading in that I thought it was a separate component on the seatpost.
ReplyDeleteGood grief... The bending fuse is a 'failure mode'. Now, what is it about the Thomson seat post shaft's design that makes it unique AND that would cause it to bend and fold instead of fracturing?
Look at your own post again and the design drawings and you'll see that while the post has an oval outer diameter (OML), the inner diameter (IML) is ovalized such that the side walls are thinner than the fore and aft walls instead of being symmetric around the entire shaft.
Intuitively, one would expect the sidewalls to deform well before the yield strength of the thicker fore and aft cross sections of the shaft were reached and thereby allow the post to fold instead of fracturing and that's what I believe is described in their Patent and conveyed in their literature, albeit in less that explicit terms.
Mark :
ReplyDeleteTrue. From the design, the major axis of the ellipse has been oriented to be parallel to the more probable of the planes of bending.
The OD of the seatpost is not oval, as you claim as it would never fit into the seat tube. The OD is circular.
Again, its all in the details. I don't have a whole lot of experience with patents, but one would think that in an official document against the invention, a complete description of what the 'bending fuse' is and in what area of the seat post this is incorporated would be stated explicitly. Patents are read by different set of eyes. What intuition led you to believe is not what someone else could see.
Hey, you were the one calling for "facts".
Since Thomson has not stated that the bending fuse is the elliptical inner cross section, I will not do so either.
Ron wrote: Since Thomson has not stated that the bending fuse is the elliptical inner cross section, I will not do so either.
ReplyDeleteGo read up on the concept and use of a 'structural fuse'.
Mark : I have heard about hydraulic and electrical fuses but this structural fuse is new to me.
ReplyDeleteI'm somewhat familiar with the steel catapult material that acts as a mechanical fuse on aircraft carriers to launch fighter planes.
Please send some well reviewed literature my way and I'll be happy to learn.
As for the discussion between the both of us, this is getting way out of hand. The failure occurred at the ear on impact. The upper faces of the ear has sharp features due to machining and one line of thinking that those could generate stress-risers cannot be disagreed with. My other question is whether a bicycle tipping over from a supporting wall that could otherwise be harmless generate enough impact torque to severe the ear of the post.
Paul at 9:32 said : 60 inch pounds = 5 foot pounds = NOT VERY MUCH PRESSURE. Without a torque wrench it would be very hard to know if it was overtightened.
A proper metalurgical analysis would reveal the failure mechanism.
60 in-lbs is not a lot of torque. You're right. Its like a 60 inch steel bar with one pound of force at the end.
60 in-lbs is not a lot of torque. With adequate experience tightening and loosing bolts, any person can go by 'feel' and tighten by hand. You don't and I repeat, you don't need to purchase a 50 dollar torque wrench just to tighten bolts on your seatpost. If you're not confident about it, hand it to your LBS and they'll take care of it.
ReplyDeleteCafiend at 9:15 : You're right. The heaviest load is the rider.
ReplyDeleteTorsional moment = Load x Moment Arm
Place a 200 pound rider at an inch away from the center of the clamp site and you have 200 in.lbs of torque. This seatpost is designed to 'give' or bend (aka yield) at 250 ft. lbs of torque, and catastrophically failing at 350 ft. lbs extreme. Now that is a huge cushion.
Marketing materials also claim the post is designed to bend at severe impact loads. Did not happen here. Maybe true for the tube itself but the ear in this case broke off.
Michael at 7:58 - Thanks for reading. I do not waste time in amassing all field reports out there, but if I find out something critical and in need of pollination, I will dig into the details and do a writeup.
ReplyDeleteThere's too many stories out there without credible sources and background info in them. For example, see
Busted Carbon, a blog that tirelessly wastes time trying to ridicule carbon fiber composites by posting anonymous pictures of broken parts, without citations and background information. You might as well think they were all photoshopped!
Do you recall how the bike fell (orientation)?
ReplyDeleteIt fell sideways. I picked it up by handlebar and the saddle and the back part broke off in my left hand.
Were you riding it when this happened (added weight) or did it free fall as it tipped over (just the bike weight).
It was leaning against the wall when it tipped over.
The broken part in question faces the north-south direction (front-rear) and doesn't stick out sideways. Which is why I'm curious. Did the seatpost also have the saddle attached during that time?
Yes, the clamp was secure and undamaged, and still attached to the saddle.
The manual was in the "useless" bag. I wonder if you ever referenced it.
Yes I did and didn't find it useless at all.
http://forums.mtbr.com/showthread.php?t=508685
ReplyDeleteHmmm. Link above is a catastrophic failure of a Thomson Layback/Setback.
Found the blog here after casually googling around for other Thomson post failures. Seems very rare.
Anon : Thanks for the tip-off. Duly noted!
ReplyDeleteThis is Dave from Thomson, email is dparrett@lhthomson.com . First, we will replace a failed part out of goodwill. Second, you simply can't generate enough force riding to break the front ear of the post. That failure is from overtorque. From past experience the bolts were probably near yield at 125+ inch pounds.
ReplyDeleteDave : Thanks for writing in. I think we all agreed that 60 in-lbs is not a lot of torque, may be hard to dial in without a torque meter and its likely the rider may have overstepped on the tightening. From his initial response to me, it seems he had been riding on the seatpost for a year without doing any work on it. So did he overtighten initially and then it failed a year later?
ReplyDeleteDid you also look at the failure of another setback post?
Here's the link : http://cozybeehive.blogspot.com/2009/04/thomson-elite-setback-post-failure.html
Would you like to comment on that?
I realize this post is over 1 1/4 years late, but i have a Thompson Elite Post that cracked in almost an identical spot. I weigh 140 lbs. was riding along (out of the saddle at the time) go to sit down and my saddle is floating. I thought for sure a rail on the saddle came loose. I stop and look and see a crack at almost the exact spot as the OP's seatpost. Very weird indeed, I have never seen anything like this at all; no impact, no new adjustment, just up and died on me.
ReplyDeleteBoycott American junk.
ReplyDeleteThis thread, and the others, make me wish I had photographed and saved all the broken Thomson seatposts and stems that's come through my shop over the past few years. I'd guess I've seen probably ten or so Thomson products with cracks, and one or two that failed catastrophically and without warning.
ReplyDeleteTheir warranty process is actually rather annoying, since they don't issue RAs (return authorizations) and no one on the phone is interested in hearing what you have to say about how or why the product failed. You just dump it in an envelope and send it back to them. Sometimes Thomson replaces them, sometimes they send the product back to you with a scribble that says "Not warranty" or some such vague comment.
Meanwhile, I've yet to see a decent cold-forged aluminum seatpost or stem fail without provocation. Mind you that these products are generally lighter and less expensive than the Thomson equivalent.
On the day after Thanksgiving, 2010, the Thomson Elite seatpost on my LiteSpeed Vortex failed catastrophically during a right turn, sending me to the pavement. Bottom line, after a trip to ER, x-rays, CT scans, and a night in the hospital, I had a broken scapula and multiple broken ribs that took 10 weeks to heal. I have a photo of the failed seat post if anyone is interested. My LBS contacted Thomson and their response was what others have reported: can't happen without extreme abuse not associated with normal riding.
ReplyDeleteIf anyone is interested in the photo, let me know.
Believe me, that's BS.
D. Holt
I have had two of these Elite posts break off at the front ear section. Yes they were torqued correctly, so thats not an issue here and I dont ride in the rain unless I get caught in it and my bikes are kept spotless, so abuse and corrosion are not an issue for this failure.
ReplyDeleteThe bikes did not have any falls either at this time or in the past so its not a striking issue to the posts etc.
Heres something thats amazed me about the breaks on these two posts, one was a 27.2 and the other a 31.6. On both posts they snapped of when the bikes were not being ridden.
The bikes were parked in my bike room and suddenly there was a "popping" sound, after which the saddle flopped down.