Help me understand carbon seatposts

[Dan Le foot]

Help me understand carbon seat posts

Hi gang.
A while back I got a lower priced. ($60)FSA carbon seatpost from Colorado Cyclist as part of a build kit.
When I torque down the Serotta collar tight enough to keep from dropping in (I’m 185lbs) I cracked the post longitudealy. (about 2”) I decided that riding it this was a bad idea.
Easton has a flat edge on their post that keeps this from happening. I put an older Easton post on the same bike and have had no problem.
So I’m in the market for a new post and I’m a little spooked about buying one other than Easton.
What do you think?
Thanks
Dan

[David Kirk]

Help me understand carbon seat posts

Hi gang.
A while back I got a lower priced. ($60)FSA carbon seatpost from Colorado Cyclist as part of a build kit.
When I torque down the Serotta collar tight enough to keep from dropping in (I’m 185lbs) I cracked the post longitudealy. (about 2”) I decided that riding it this was a bad idea.
Easton has a flat edge on their post that keeps this from happening. I put an older Easton post on the same bike and have had no problem.
So I’m in the market for a new post and I’m a little spooked about buying one other than Easton.
What do you think?
Thanks
Dan

There are a few things to consider. The first one is that not all carbon post are created equal. Frankly some are crap. The way they orient the fibers during the layup can make them resistant to crushing or not. Typically post that are a bit heavier have the type of layup that will be able to deal with both the bending loads and the pinching loads that the frame imparts to the post.

There is another thing too. Seat post diameter. A 27.2 seatpost is not supposed to be 27.2 in diameter but it designed to fit into a 27.2 hole. This means that the post should be in the 27.15 range for a nice slip fit. The problem in some case is just the simple fact that the post is a bit too small and that the frame ends up crushing it instead or wrapping around it. Not good. The other thing very few folks will admit to is common practice. Most posts are made a bit too small and then the epoxy is laid on until the post is the proper diameter. This can work OK but can also lead to problems. Epoxy (or clear coat paint in some cases) is not that hard and can compress and lead to the post slipping................ so you tighten it more and more until it stops slipping. But in some cases this can lead to the post fibers being crushed before thing hold firm.

So all this said I don't have a firm answer for you. I'm pesonally not an expert in carbon posts. I have a Reynolds post which works very well but I think that they are focusing on wheels and have stopped making their kick butt posts.

Good luck.

Dave

[GuyGadois]

IF you own carbon components and work on your bike yourself then a torque wrench is mandatory. Not cheap but neither are cabon components.

[Onno]

Could someone explain why carbon seatposts are even necessary? They aren't for the most part lighter than high-end aluminum ones, and they clearly aren't stronger. So why bother? Is it just to complete the carbon look?

[Dekonick]

also - get the seat post ring/collar mady by campy - it has a more gentle squeeze than the typical collar.

[Dekonick]

Could someone explain why carbon seatposts are even necessary? They aren't for the most part lighter than high-end aluminum ones, and they clearly aren't stronger. So why bother? Is it just to complete the carbon look?

I do it cuz my frames are titanium and I dont want to risk it. Not necessary, but Ti posts are hard to find.

[edl]

Because carbon is the uberwondermaterial, it is faster, smoother, and lighter! :D

I have a Gunnar Roadie and a Gunnar Street Dog, very similar frames with similar wheels/tire setups - one has a CF post, the other has an Aluminum post. I can't tell the difference.

I put on Al stems, seatposts, and bars when upgrading. I'm a bit skeptical of CF for those parts, and since Al can usually be done at a lower price point and comparable weight it makes sense to me.

[zap]

Try some Tacx carbon assembly paste next time.

Further to what Dave posted, I found that some carbon posts have varying dia. up and down the post.

So, best bet is to measure the post with a caliper and if that checks out, apply assembly paste and torque to minimum spec.

[Onno]

I do it cuz my frames are titanium and I dont want to risk it. Not necessary, but Ti posts are hard to find.

I have a titanium frame and Thomson seatposts, and have never had any problems of any kind.

[RPS]

When I torque down the Serotta collar tight enough to keep from dropping in (I’m 185lbs) I cracked the post longitudealy. (about 2”) Dan, do you grease it?

[Big Daddy]

some are all carbon

some are carbon wrapped

BIG difference.

Always use carbon compound esp when carbon on carbon contact occurs.

torque wrench is mandatory. I don't care how long you have been wrenching. You will get it wrong.

Enjoy the CF. Everyone needs fiber in their diet.

[Dekonick]

I have a titanium frame and Thomson seatposts, and have never had any problems of any kind.

Like I said, not necessary - but why risk it?

[Dan Le foot]

Dan, do you grease it?
My understanding is not to grease the carbon post. It was going into an Ottrott (ti) seat tube..
Dan

[Dan Le foot]

Thanks Dave.
Sounds like the FSA post is a piece of crap. But what do you want for $50? :crap:
Dan

There are a few things to consider. The first one is that not all carbon post are created equal. Frankly some are crap. The way they orient the fibers during the layup can make them resistant to crushing or not. Typically post that are a bit heavier have the type of layup that will be able to deal with both the bending loads and the pinching loads that the frame imparts to the post.

There is another thing too. Seat post diameter. A 27.2 seatpost is not supposed to be 27.2 in diameter but it designed to fit into a 27.2 hole. This means that the post should be in the 27.15 range for a nice slip fit. The problem in some case is just the simple fact that the post is a bit too small and that the frame ends up crushing it instead or wrapping around it. Not good. The other thing very few folks will admit to is common practice. Most posts are made a bit too small and then the epoxy is laid on until the post is the proper diameter. This can work OK but can also lead to problems. Epoxy (or clear coat paint in some cases) is not that hard and can compress and lead to the post slipping................ so you tighten it more and more until it stops slipping. But in some cases this can lead to the post fibers being crushed before thing hold firm.

So all this said I don't have a firm answer for you. I'm pesonally not an expert in carbon posts. I have a Reynolds post which works very well but I think that they are focusing on wheels and have stopped making their kick butt posts.

Good luck.

Dave

[RPS]

My understanding is not to grease the carbon post. It was going into an Ottrott (ti) seat tube..
DanJust checking since grease or any lubricant lowers friction, making it necessary to tighten more to keep from slipping. And of course that increases chance of crushing.

Dan, on one of my carbon posts the manufacturer recommended reversing the clamp to get more even tightening. However, it looks odd when you do that; although it's an indication they are aware of the potential problem.

So far I've had good luck with the few carbon posts I've tried from three manufacturers, but I ride in the 150 pound range so they don't take much abuse.

[PoppaWheelie]

Try some Tacx carbon assembly paste next time.



+1. This solved any slip issues for me...and I also use it on my stem and bar clamp areas. If you can't get assembly paste at your LBS (or don't want to bother) than you can also mask off a 2 or 3 inch band on your seat post and spray-on a two or three layers of old-school Aqua-Net hairspray. Let it dry for an hour or so between coats and before you install it. This also solved a bad slip issue for me and will wash off easily with water if you want. Not sure about how it will perform long-term if you ride in the wet tho'.

[abqhudson]

Just my experience: A Specialized Pave Pro Carbon seatpost rides noticeably different from any other carbon, Al, or Ti seatpost I have tried - at least 4 alloy, at least three different carbon inc campy, at least three different Ti inc Campy and Eriksen. I have found the same differences to be true of handlebars. My present favorite is the Reynolds Ouzo Pro Round. YMMV.

[Bob Ross]

I do it cuz my frames are titanium and I dont want to risk it. Not necessary, but Ti posts are hard to find.
Like I said, not necessary - but why risk it?


Risk what? What do you think you're risking by not using a carbon seatpost on your Ti (or any) bike?

[Kane]

Torque wrench vs. the click type. The park torque wrench never gets off spec due to spring fatigue or dropping. It has a better feel than click types and it is cheaper, (but not by much anymore).

cheers,

Kane

[Onno]

Risk what? What do you think you're risking by not using a carbon seatpost on your Ti (or any) bike?


I was just about to post the same question. Seems to me you've shown there's more risk in using a carbon seatpost.

[Ahneida Ride]

Like I said, not necessary - but why risk it?

Al is almost as light. why take the risk?

[alancw3]

a fsa offset carbon post came on my c'dale six13 and i used it for a thousand miles or so before buying the exact same fsa in zero offset. now have 7000 + miles on the six13 and never a problem with the post. i am a big guy at 6'4" and 215. once i adjusted it i have never touched it since. aluminum seat tube to carbon post. no lubricant.

[Dave]

I never buy any seatpost that does not have a 2-bolt clamp system to allow very fine angle adjustments. Any other type is crappy, IMO. I've had no problem with FSA K-force light carbon posts or ITM Millennium (Selcof) carbon posts.

Using Tacx assembly paste is a good idea and it might be wise to check that seat tube ID to be sure it's not oversize.

I've never used a torque wrench on any seatpost or stem bolt attached to a carbon frame, carbon steerng tube or carbon bars. I never intend to rely on a torque wrench to tighten these bolts. It just should not be necessary, it the mechanic has a reasonably skilled hand. If a torque greater than 9Nm is required on a bolt to prevent seatpost slippage, then there is a fit-up problem. If this torque cracks something, there is a fit-up problem and/or a crappy product.

[mike p]

I use a fine grit polishing compound when installing seatpost. You don't need to tork near as hard with it. No slippage and I weight same as you. Before I started using it I couldn't get a carbon post to stay in place.

Mike

[chuckred]

I never intend to rely on a torque wrench to tighten these bolts. It just should not be necessary, it the mechanic has a reasonably skilled hand.

I hope you don't work for the airlines!

[Dave]

I hope you don't work for the airlines!

I quit working when I was 50 - five years ago. FWIW, I've never had problems with post, or bar slippage and I've never broken a bolt or stripped threads on any bike component. I do use a torque wrench, but only for high torque items like BBs and cassette lockrings.

I once tried to crack a piece of scrap steering tube by tightening a stem onto it that had two M6 bolts and couldn't do it. I tightened the stem to a ridiculous torque with a long handled hex wrench and got no damage at all. I didn't have a compression plug in the steering tube either. Most failures are either due to some bad fit-up problem or simply a defective layup in the carbon component, not the difference between 7 and 9Nm of torque.

[Johnny P]

I think its best to use a carbon seat post with a titanium frame because an aluminum one can bond to the Ti frame. Then the post can never be removed or adjusted without replacing the seat tube. :eek:

[Fixed]

carbon why was it ever used in the first place ?
there is nothing about it .. i like ..i just don't dig it imho that is me though
cheers

[Tobias]

carbon why was it ever used in the first place ?
there is nothing about it .. i like ..i just don't dig it imho that is me though
cheersPound for pound it's stronger than steel, titanium, or aluminum. You can also make some cool parts out of it that can't be made out of these metals.

When weight affects performance like say in airplanes, carbon fiber can find many uses. If not for high cost we'd see a lot more of it.