big john

I've broken a number of posts and saddles and other stuff. I started using Thomson posts years ago and never had a problem with one of them. I wouldn't recommend a cf post for you.

Eric F 

You didn't specify before, and based on your other comments, sanding a carbon post doesn't seem out of character. You have concluded that carbon fiber seatposts are a bad idea, yet the failure seems to be directly related to your own misuse of the item.

jp911

Brand incompatibility can lead to spontaneous carbon fiber failure: Bontrager post on a Specialized frame...tsk, tsk.

icemilkcoffee 

Looks like it's breaking right at the min insertion marks. I don't think you did anything egregiously wrong.
Carbon seatposts are just more prone to slipping period. Carbon paste help a little but certainly doesn't do miracles. If you are a heavyweight, cf seatposts might not be for you.

wolfchild

It's not unusual for carbon to fail catastrophically even when used correctly. The risk of failure is magnified especially for heavier riders or when riding over rough terrain and roads.

spelger

i think we'd hear more of this were it true.

veganbikes

1. Carbon generally does not just fail randomly, there are reasons for it. Sometimes it is abuse or improper installation or just quality of components or a QC error that was not gotten. Things don't just randomly fail just because there is a reason.

2. A mechanic did not install that seatpost above the minimum insertion line nor do I believe they improperly torqued it. I believe it was probably installed properly or close to it and was modified by the rider or maybe possibly but unlikely someone who was acting as a mechanic at a shop decided to just do whatever who cares. However that seatpost and those torque specs exist for a reason and if you cannot be bothered to use them and recognize them maybe having a seatpost and seat collar is just not for you.

3. Do not modify carbon components leave them alone to manufacturer specs. The manufacturer designed those components as they are and if they felt like they need to sand them down or modify them in other ways they would have done so at the factory or in the R&D phase. That can easily cause issues and get you hurt.

4. Take responsibility for your bikes people. Take care of them and treat them well and they will take care of you. If you aren't good with wrenching take it to a good shop or if you are in a crash take it to a shop. Have someone who knows what they are doing look over the bike and make sure it is in tip-top shape. No need to get hurt.

genejockey 

Big Carbon suppresses it.

LarrySellerz

In case it wasn't clear, I suspect that the seatpost was damaged at some point prior to the latest installation which was done by an experienced mechanic. The noteworthy thing about this is that the damage went unnoticed him and I until it suddenly failed.

spelger

what ever was i thinking?

Keefusb

I had a similar incident recently with a Kalloy aluminium seat post. Granted, I'm a big dude (6'3" and 215#) but in 30+ years of serious riding, I never had an aluminium seat post fail in the middle of a ride. I now have a heavy, but bulletproof 90's vintage 400mm Profile seat post installed and no problems whatsoever with the seat post bending then breaking.

veganbikes

No that seatpost was not installed by a mechanic please do not say that. You are welcome to admit you installed yourself or say you had some random person installed but no actual mechanic put it above the minimum insertion line. Especially with such a clearly marked minimum insertion line. If you are too tall for the component like in this case make sure you get more appropriately sized parts or probably a bike that is more appropriately sized.

Fredo76

Were seatposts that break considered an advantage at one time?

rosefarts

The craziest thing about this thread is that he doesn’t have a set of metric Allen wrenches.

LarrySellerz

A mechanic did install that seatpost, please don't say that i'm just flat out lying. He was trying to make it work for me and we discussed that it was too high, but I doubt that was the root problem.

veganbikes

That was the problem, that seatpost was too high and caused problems. There is a reason they put those marks on there and not just for a cool pattern. If an actual mechanic had seen that set up they would have told you, NO that seatpost is too high and you need a proper frame that fits you and then if they refused they would probably say at least get a longer seatpost. No proper mechanic set up a seatpost above the minimum insertion line. Maybe someone playing a mechanic did it but a mechanic is not going to intentionally put someone's life at risk like that. Nor are they going to suggest sanding down a carbon seatpost.

The root of the problem is someone deciding to ride a frame that is too small and put a seatpost over the minimum insertion line and not maintaining a bike properly and not accepting the facts of all of this. Ride the right size frame keep your seatpost below the minimum insert line and take care of your bikes especially if you crash on them.

Eric F 

This is false.

LarrySellerz

The frame is the right size and I never sanded carbon....


I suspect the bulk of the damage was done when the seatpost was on a bike that was much too small for me, and was extended much further. Or a prior owner damaged it. In any case, it passed numerous inspections after it was presumably damaged. The final installation was not ideal, but I doubt it is bad enough to be the root cause.

jaxgtr

This is what I took to you sanding the post...

veganbikes

Ok fair dinkum, you did mention sanding a seatpost and we are talking about a seatpost.

The frame is likely the wrong size, on a properly sized frame you WOULD NOT need to put the seatpost above the minimum insertion line as you did. It could be that the seatpost is extra short but then why would you run it if it was so short when they make plenty of longer posts including some of carbon. I doubt that seatpost was inspected. I am sure you looked at it and said yeah that looks fine as someone might who may not know what they are looking at but I doubt it was pulled and x-rayed or tested in any way. If you did have the seatpost above the minimum insertion line on other bikes that would cause issues as well. You can split hairs but in the end your reckless abandon for the minimum insertion line was the problem. I am going to say the prior owner did not damage it, yes that is possible in some situations and why I probably would avoid used carbon but seeing where it broke and hearing you talk about it, I am pretty confident this is on you, bud.

Look it is OK people make mistakes it happens. That is why they have that minimum insertion line on there to try and help folks so they don't break a seatpost, same thing with torque specs to try and help prevent these sort of things but yeah people can easily overlook them and say ahhh not for me and then have issues. For those folks I recommend good quality extra long alloy posts and a good mechanic to help them. That will give you a little more margin for error. However now you have the chance to learn from this hopefully and just use a torque wrench make sure more of the post is in the frame especially enough to be below minimum insertion and especially more for a bigger rider and have a mechanic check over things with some more regularity.

squirtdad

this does not compute, have nice park workstand, but not metric hex wrenches??

MaxKatt

Probably rode nice and cushy with all the flex. Right before the crack of course. You flew too close to the sun. But, as they say, if you’re not living on the edge, you’re taking up too muck space. Well done.

LarrySellerz

The seatpost came from this bike, the shop swapped them for me when I brought both bikes in for work. The bike it broke on is a 58.

veganbikes

Unfortunately much of what Little Larry says does not compute though in the movie I don't think he actually ever talked nor did his father in the iron lung (Arthur Digby Sellers, writer of a large portion of Branded). Pilar the housekeeper said everything!

veganbikes

That is even more problematic, if you are riding a 47cm and you need a 58 or probably larger. None of that is good and that minimum insertion line is still there for a reason and I still have extreme levels of doubt on the shop setting any of those seatposts above the minimum insertion line. I can believe they swapped them but I doubt they just left it above the minimum insertion line, I would love to talk to the faux mechanic who said that was safe and good to go.

Get a properly sized bike and you will be less likely to have minimum insertion issues.