Carbon Seatpost on a Steel Frame?
- Thread starter Chance3290
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It could only really make a difference if you started with an old, 5kg, built-like-a-tank steel mtb frame with an equally caveman-like steel seatpost, and you swapped the post for a carbon one. And even then you'd need to be riding long distances to notice anything. If we're talking road frames, then, as boudreaux said.
It is more dependent on the ammount of seat post that will be exposed. If it is a tall frame then the effect would be minimal at best. A small frame/tall rider would notice much more.
FWIW, I recently bought a carbon seat post at the Madison bike swapmeet. It was an odd diameter and no one wanted it, so I got it for $4, including a seat.
This particular post is made for a Dahon folding bike, and is nearly 2' long. After taking off the seat, it doesn't feel any lighter than an aluminum post (if one found an aluminum post that long) to me. I think the CF construction is intended to appeal to a certain marketing niche.
I am going to cut the post up for use in a CF recumbent that I am planning on building when the weather warms up a little. It is about the right diameter to mount a front derailleur, so a short piece of it will end up right next to the crankset. The rest will be used to join the rear fork tubes.
TD
This particular post is made for a Dahon folding bike, and is nearly 2' long. After taking off the seat, it doesn't feel any lighter than an aluminum post (if one found an aluminum post that long) to me. I think the CF construction is intended to appeal to a certain marketing niche.
I am going to cut the post up for use in a CF recumbent that I am planning on building when the weather warms up a little. It is about the right diameter to mount a front derailleur, so a short piece of it will end up right next to the crankset. The rest will be used to join the rear fork tubes.
TD
The thing to keep in mind with carbon construction is that it is simple to make it strong. It is simple to make it light. It is hard to make it Strong and Light. If a company does not feel confident or have the engineering prowess to make a strong and light one, they will make a strong one. Simple business practice. The Easton composites and Bontragers are light and strong, but they have immense engineering to back that up.tyler_derden said:FWIW, I recently bought a carbon seat post at the Madison bike swapmeet. It was an odd diameter and no one wanted it, so I got it for $4, including a seat.
This particular post is made for a Dahon folding bike, and is nearly 2' long. After taking off the seat, it doesn't feel any lighter than an aluminum post (if one found an aluminum post that long) to me. I think the CF construction is intended to appeal to a certain marketing niche.
Don't forget that not all carbon fibers are created equally. Lower end manufacturers use cheaper raw materials and subsequently have to use more material to get the same strength.Wurm said:
Aw, come on...let the man put a carbon post on his steel bike. He may or may not realize a difference in ride feel or weight but he would definately be adding the cool factor.
IMHO, regardless of r&d and brand name, I think carbon just plain old looks cool.
Depending on his frame it could be overkill. A little overkill is not a bad thing, is it?
Jerry
IMHO, regardless of r&d and brand name, I think carbon just plain old looks cool.
Depending on his frame it could be overkill. A little overkill is not a bad thing, is it?
Jerry
"He may or may not realize a difference in ride feel or weight but he would definately be adding the cool factor."
Nothing wrong with chi-chi, hey looks do count for something for sure. But I'm talking about a post that's built well enough to hold up. He might realize the difference in "ride feel" if the damned thing breaks from being a cheap POS!! Me being a 200 lb'er, I think about those things.
Nothing wrong with chi-chi, hey looks do count for something for sure. But I'm talking about a post that's built well enough to hold up. He might realize the difference in "ride feel" if the damned thing breaks from being a cheap POS!! Me being a 200 lb'er, I think about those things.
I hear you Wurm.
Me, having never been over 150 pounds tend not to think about those weight issues.
I confess...I have a carbon seatpost from Litespeed and have in the past ridden Easton. I don't think I could "really" tell a difference in ride quality. I'm a fairly new rider after a 20 something year hiatus so I guess I haven't ridden long enough and have not ridden enough different components to truly be able to tell the subtle differences between them all.
Reputable r&d is a factor in my decision making process.
Have you ever heard of a carbon anything breaking? I haven't. I'm sure it could though.
Jerry
Me, having never been over 150 pounds tend not to think about those weight issues.
I confess...I have a carbon seatpost from Litespeed and have in the past ridden Easton. I don't think I could "really" tell a difference in ride quality. I'm a fairly new rider after a 20 something year hiatus so I guess I haven't ridden long enough and have not ridden enough different components to truly be able to tell the subtle differences between them all.
Reputable r&d is a factor in my decision making process.
Have you ever heard of a carbon anything breaking? I haven't. I'm sure it could though.
Jerry
I doubt anyone would be able to tell a difference in the ride between any 2 CF posts, and some say there's really no diff between any seatpost in ride quality - CF, Ti, Al, steel or whatever. Mostly done for weight reasons and chi-chi factor.
Yes, I have heard of CF parts breaking. Who was it that broke a handlebar in the TdF last year? Or it was a stem I don't remember which. And I have seen a couple of reports, but only one or two, of heavier guys breaking CF posts.
It does happen, but whether CF fails more or less often than other materials I don't know.
Yes, I have heard of CF parts breaking. Who was it that broke a handlebar in the TdF last year? Or it was a stem I don't remember which. And I have seen a couple of reports, but only one or two, of heavier guys breaking CF posts.
It does happen, but whether CF fails more or less often than other materials I don't know.
If it is made propperly it is of comparable strength to the other materials. It has a different failure mode than metal however. It loads on an even stress level, which makes it strong normally, but if it is chipped deeply or scored it will make a stress concentration. At this concentration it will be prone to cracking. For this reason you should inspect the entire length of these items frequently. If in doubt about a part, Easton will test it for you for free(shipping maybe). Thats another perk of a big company.
Yes, CF is strong as long as it doesn't get scratched or scored beyond light scuffs. Easton now has the nanotube technology which looks to be very promising - it strengthens CF quite a lot.
I've seen this tech talked about on science shows, but I didn't think it would come around so soon, and not so much for bike components. They're using it on their new forks and CF rims so far. I don't see it yet in their seatposts and stems, but maybe it's not needed for them?
CF or Al, Easton makes great stuff IMHO. I really like my EA70 bars.
I've seen this tech talked about on science shows, but I didn't think it would come around so soon, and not so much for bike components. They're using it on their new forks and CF rims so far. I don't see it yet in their seatposts and stems, but maybe it's not needed for them?
CF or Al, Easton makes great stuff IMHO. I really like my EA70 bars.
I'm not sure what you mean by an even stress level. Both carbon fiber and aluminum will suffer crack nucleation around chips and scratches. The additional failure mode in carbon fiber is interlaminar matrix fracture. Stress waves caused by impact loads which may not even scratch the finish can initiate cracking in the composite matrix. Subsequent cyclic loading then causes these cracks to propagate between the laminate plies. Eventually the whole thing will delaminate spontaneously. Short of having your parts x-rayed once a month, you're probably not going to catch this before it happens.Conniebiker said:
Appreciate your expertise here. Just to clarify, you didn't mean to imply that spontaneous delamination always means catastrophic failure of the part, did you? Can't a well-designed composite structures maintain sufficient strength despite some pretty significant delamination?artmichalek said:
Agree not to worry about inspection, X-ray or ultrasonic testing on a routine basis. Take a very close look after a crash, or if you hear or feel any unusual flexing or creaking. Other than that, just ride.
Seems to me a seatpost is a tough application for CF. I favor a high-quality AL post, like the Thomson Elite.
A damaged part may or may not fail catastrophically, depending on how the it's loaded. If the delamination occurs in a spot that's in compression, the fibers are going to buckle without any warning.dhk said:
Personally I wouldn't ride any carbon part again after a crash unless I was absolutely sure it didn't hit the ground. The biggest problem with interlaminar matrix cracking is that you aren't going to experience any flexing or creaking until it breaks all the way.
Back to the original topic, the seatpost is one of the most straightforward parts on a bike. Some manufacturers might be able to make one a little bit lighter, but it's a hard thing to actually screw up. A cheap one isn't actually going to be dangerous unless it's been handled roughly.
That's what I've always thought. No matter what the rider may weigh, there's still a significant amount of force concentrated on a fairly small amount of material in a seatpost, and a constant rocking back & forth with nearly the rider's full weight upon it.dhk said:
At least with CF rims the load is /2, and on a fork you have much more material and 2 legs to go through, except of course for the steerer tube.
I need to contact Easton and press them on this nanotube stuff. Looks very promising.
Technical link
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To clarify on the failure modes.
I was referring to cyclic loading within design parameters. Yes AL is sensitive to this too. Within parameters, the carbon part will not have an appreciable service life limit, assuming no delamination.
If the parameters are exceded, or suspected to be exceded, it should be tested. The reputable makers reccomend that you do send them in if you suspect the part. Beats a lawsuit.
Cool on the nanotech.
I was referring to cyclic loading within design parameters. Yes AL is sensitive to this too. Within parameters, the carbon part will not have an appreciable service life limit, assuming no delamination.
If the parameters are exceded, or suspected to be exceded, it should be tested. The reputable makers reccomend that you do send them in if you suspect the part. Beats a lawsuit.
Cool on the nanotech.
