Seatpost Design Discussion for Engineers

[Dirtbreath]

 

Dirt Breff (as Nancy calls it)

 

I have edited' date=' hope you are glad, I simply cannot understand why there has to be a skepticism towards ALL manufacturers (hope that clears it up)

 

I wish I could give you an honest opinion however none of us are qualified enough to give an opinion unless we have the actual post in our hands and do various tests around the actual product.

 

Unless this gets done, I believe that every opinion is simply speculative.

 

 

 

I do however think that this particular rider must have had a crash or two or several and that could have weakened the post in that area, not cleaning his bike and inspecting it properly, he might not have seen a small crack that might have developed, from crashing (my opinion of course and just my speculation)

 

 

 

Jagwil said it could be the material, I feel that the post in question should go to Thomson for an analysis.

 

 

 

As Mampara said as well, this kind of stuff happens, should we accept it, if it was poor manufacture.

 

My answer is no, but this is not something we see on a Thomson post everyday so it's out of the norm for Thomson which casts a shadow of doubt as to what "MIGHT" have happened.

 

 

 

Just out of interest, I am going to guess that the second post in the picture is a Masterpiece, I would love to know the weight, size, type of bike and riding style of the owner regarding said post.

 

 

 

[/quote']

 

Thanks for that. I do think Nancy pronounces it better before a few beers.

 

I ride a Thomson and swear by it. But then again it hasnt broken and I honestly dont know of many components that simply break like that. I am genuinely curious if it is just a dud post or whether something was done during use or installation that we could avoid.

 

I think there are many such cases where the manufacturer should test and respond but normally stays silent because it is a once off and well, these thing can happen.

 

To be honest, I dont think regularly ridden bicycles undergo such heavy stresses and shouldnt fail like this during normal use.

 

I think the same goes for carbon. Just because rally cars use carbon for skid plates and the like doesnt mean its bullet proof. An F1 car uses carbon for suspension components. Have you seen how those things pop when touched in an awkward angle.

 

I have been following some threads on another forum about Yeti carbon swingarms and their failure. I have abused mine quite considerably and should it fail I would never be able to put my hand up and shout foul.

 

Same goes for another thread here about a carbon frame which has clearly taken one hell of a knock.

 

[kennyg]

I worked in the motor industry, we did risk analysis on specific manufacturing faults, it is a top end manufacturer with a serious focus on their internal quality processes.

Almost every car produced has a flaw of sorts( that is known, might be many more that are not known), if the customer can see or experience the problem to a high degree, under "normal" conditions, then we actually do something about the problem. Recalls, are seriously expensive and many times the manufacturers will happily replace a couple of broken parts or entire units if that is indeed the case. To put this back onto the current argument, Thomson will probably argue warranty periods, most of these new age products only have a 2 -5 year design life anyway.

 

All we as the customer can ask is that the manufacturer does their best to prevent known problems. Otherwise we will all end up completely paranoid...of what might happpen. The second thing we ask is that if the problem is actually caused by the manufacturer that they are prepared to help in the situation.

 

The American market has some serious liability issues, so they will cover themselves to a significant degree.

[Domestiquehated]

I think that the rider was evasive - bikes leaning against a wall don't just "fall over" and how can he answer "Not that I remember" when asked if the bike was involved in any crashes.  Or does he crash so often on his other bikes that it all becomes a bit blurrey?  I remeber every one of my crashes: where, which bike, what my excuse was, etc...

[Dirtbreath]

 

Dirt Breath

 

 

 

You grilled me' date=' but I have posted for a reason.

 

I cannot see the purpose of a topic like this besides that it will cause some doubt in the minds of some folks.

 

If you would like to, give me a call and we can talk Thomson.

 

I will gladly also post pics of a Masterpiece and an Elite to show the differences if you all would like that.

 

Windblown

 

You don't have anything to worry about, I have never had a single Thomson failure in my hands.

 

Splat you mak a valid point and I made mention to this in an earlier posting.[/quote']

 

You are so sensitive. Thats not a grilling. PM sent.

 

I use a Thomson seatpost that has been ridden pretty hard and has seen some nasty flips. The scuffs on the saddle are a testament to that. Its shows absolutely no sign of any weakness. It is currently totally stripped for a full clean so I can attest to that.

 

[Wyatt Earp]

 

Dirt Breath

 

 

 

You grilled me' date=' but I have posted for a reason.

 

I cannot see the purpose of a topic like this besides that it will cause some doubt in the minds of some folks.

 

If you would like to, give me a call and we can talk Thomson.

 

I will gladly also post pics of a Masterpiece and an Elite to show the differences if you all would like that.

 

Windblown

 

You don't have anything to worry about, I have never had a single Thomson failure in my hands.

 

Splat you mak a valid point and I made mention to this in an earlier posting.[/quote']You are so sensitive. Thats not a grilling. PM sent.I use a Thomson seatpost that has been ridden pretty hard and has seen some nasty flips. The scuffs on the saddle are a testament to that. Its shows absolutely no sign of any weakness. It is currently totally stripped for a full clean so I can attest to that.

 

Not sensitive at all, sorry man, grill was maybe too harsh.

 

PM sent

[Thug]

I've had a Thomson Elite seatpost and X4 stem on my Santa Cruz for the past 2.5 years.

 

My bike has seen plenty of action on trails throughout Southern Africa, on the beach, through rivers etc and both items still look as good as new.

 

No matter how well something is made, items do fail from time to time and this probably represents 0.00000001%  of all the seatposts Thomson has manufactured

 

And, as has been mentioned I'm sure the owner is not telling the whole truth.

 

I'd have no hesitation in purchasing Thomson seatposts and stems again !

 

 

[Johan Bornman]

 

Do you spend your entire day looking for discussions around hearsay or sensationalism ?
Are you so skeptical about all types of manufacturers that you alw ays have to find some way to slander them' date=' or try and find fault or insinuate that they don't know what they are doing ?

I will add my 1 c worth to this topic.
cut cut cut cut cut

 

 

[/quote']

 

Just in case someone wonders what was edited out. 

 

An edit is not the same as an apology.

 

 

 

 

 

[Dirtbreath]

 

 

Do you spend your entire day looking for discussions around hearsay or sensationalism ?

Are you so skeptical about all types of manufacturers that you alw ays have to find some way to slander them' date=' or try and find fault or insinuate that they don't know what they are doing ?

 

I will add my 1 c worth to this topic.

cut cut cut cut cut

 

 

[/quote']

 

Just in case someone wonders what was edited out. 

 

An edit is not the same as an apology.

 

 

Let's talk seatposts Johan. Do you think this guy has been totally honest in his reason for the failure?

 

[Johan Bornman]

My intention with this post was to initiate a discussion about the dilemma bicycle manufacturers have. They are required to constantly reduce component weight yet, keep durability at an acceptably safe level.

 

GreatWhite and I discussed this once and his take on this was that most high-end components are sacrificial components that shouldn't be considered as durable enough for long-term use.

 

As true as that may be, it sill poses a dilemma for marketing a product. How do you tell your customer that the product is light but actually only be used to ride to church on Sundays?

 

We're in an unusual situation with cycling - I cannot think of another industry in the same boat - where weight reductions are required at a higher rate than new lighter materials can be developed and tested.

 

The UCI recognises the problem and posed a mimimum weight limit on bicycles. The industry responded by bragging that their bikes are so light, they're illegal. Note, not so light that they're unsafe for continued athletic use, but so light that they're illegal.

 

Users of those bikes simply put some lead under the saddle to bring it up to the required weight. A more responsible approach would have been to put in a stronger seatpost or stronger stem or whatever may be the case.

 

At least in professional circuits they have the luxury of replacing their components often - at least once a season. You and I squeeze as much life out of our equipment as we can. The only limits we impose on ourselves are fashion and physical failure.

 

The paper I cited also had a nice section on the Patents Thompson obtained on the post. The point was made that the claims mention a "fuse", a part that fails safely, indicating that the post is past its serviceable life. However, the fuse's mechanism isn't cited. I found that quite interesting and after searching on the US Patent website, couldn't find it either. Such a "Fuse" would be great in all bicycle components.

 

 

Back to the engineering of the post and its mode of failure. Many of you mention crashes. A crash is generally not catastrophic on components, especially not seatposts. A bike is light and bounching around on its handlebars and saddle does little damage to these components. They could bend if the force is greater than the yield of the material.

 

However, a bend is a nice "fuse" - end of life is indicated clearly.

 

What happened here is the more dangerous mode of failure - fatigue. Fatigue is caused by normal use and almost always results in cracks that suddenly and precipitously lead to complete failure.

 

The point was made that the only safety net between a seatpost colonostomy and escape was a flimsy saddle bag. This brings me to the point that certain components fail with disastrous effects - seatposts, stems and forks, I'll classify as the worse. Frames, seat rails, wheels are minor in comparison.

 

I recognise Thomson as a superb company taking great care in what it does. However, in all the litererature I looked at, I only see load tests being done on the posts - i.e. it was loaded with X weight and still survived. The trick is to do cyclical load test that simulate riding over time and distance. I see no mention of that made. After all, fatigue (with cracking) is the danger, not a buckled post.

 

I didn't post this as an indication of a good or bad manufacturer, that's irrelevant. I posted this hoping to stimulate an intelligent debate around our industry's dilemma.

 

 

 

 

[Johan Bornman]

Let's talk seatposts Johan. Do you think this guy has been totally honest in his reason for the failure?

 

Once you understand that the issue is not about a crash but about fatigue, I think he is honest.

 

When materials are so thin as to be just-just strong enough to do the job, there is no margin for error. The slightest flaw in the tubing will lead to a disastrous failure. If the tube was thicker, that same flaw would have resulted in a gradual failure that would have give the rider more warning.

 

Today's long unsupported seatposts (on sloped top-tube bikes) coupled with heavy riders are a recipe for danger.

 

 

[Dirtbreath]

I will use the Thomson post as the expample as this is where we started.

 

I have a Thomson post that has seen many hard hours with a heavier than average ass suspended not to high over it. Not to say it wont fail but it hasnt happened yet. I am really not aware of seatpost and stems failing regularly. Is it more common than how I understand it that it is a problem.

 

[Bos]

GreatWhite and I discussed this once and his take on this was that most high-end components are sacrificial components that shouldn't be considered as durable enough for long-term use.

 

As true as that may be, it sill poses a dilemma for marketing a product. How do you tell your customer that the product is light but actually only be used to ride to church on Sundays?

 

We're in an unusual situation with cycling - I cannot think of another industry in the same boat - where weight reductions are required at a higher rate than new lighter materials can be developed and tested.

 

The UCI recognises the problem and posed a mimimum weight limit on bicycles. The industry responded by bragging that their bikes are so light, they're illegal. Note, not so light that they're unsafe for continued athletic use, but so light that they're illegal.

 

Users of those bikes simply put some lead under the saddle to bring it up to the required weight. A more responsible approach would have been to put in a stronger seatpost or stronger stem or whatever may be the case.

 

At least in professional circuits they have the luxury of replacing their components often - at least once a season. You and I squeeze as much life out of our equipment as we can. The only limits we impose on ourselves are fashion and physical failure.

 

 

Very good Point Johan...

 

We are half driven by a consumerist Market trend and expect "trust" the manufacturers with everything they Produce.. We dont question the Strenth and simply beleve the marketing Hype which Is almost never backed up..

 

This morning I was sitting on the BOG when reading up about Easton's new Road crankset..400% stiffer, lighter, 12% this and that....then the competition..

Because they are dishing out some numbers we just beleve them.

And unless there has been a breakthrough in technology of carbon manufacturing..

 

which there probably have over the passed 3-4 years...

BUT NOT AT THE SAME CURVE AS WHAT THINGS ARE GETTING LIGHTER BY...

 

Thanks.. I feel much more proud of my 13KG FS with reasonably light components on them now

[NotSoBigBen]

I will add my 1 c worth to this topic.
I have been riding and installing Thomson posts for around 7 years now and I have NEVER' date=' and I repeat NEVER seen that type of failure on a Thomson seatpost.
There must be something fishy that has happened to that post.
Do we have proof that he , the user is telling the truth ?[/quote']

 

 

Boris you reckon he were not JRA'ing

[Johan Bornman]

I am truly confused. What is the question?

 

 

Edit: Referring to Dirtbreath's last question.

Johan Bornman2009-04-17 04:19:58

[NotSoBigBen]

Sorry JB, Boris will know ............

[Roders]

 

Once you understand that the issue is not about a crash but about fatigue, I think he is honest.

 

When materials are so thin as to be just-just strong enough to do the job, there is no margin for error. The slightest flaw in the tubing will lead to a disastrous failure. If the tube was thicker, that same flaw would have resulted in a gradual failure that would have give the rider more warning.

 

Today's long unsupported seatposts (on sloped top-tube bikes) coupled with heavy riders are a recipe for danger.

 

 

 

 

Manufacturers are constantly pressurized into making lighter & lighter equipment, and this has to come at a price, ie longevity. But I think they reason with todays culture of more frequent equipment upgrading and changing, "to keep up", their equipment does not have to last as long, so for a component to have lasted 3+ years, its already past is usable life.(Probably in the small print somewhere)