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PostPosted: Wed Jan 23, 2013 2:32 pm 
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Joined: Sun Jun 05, 2011 10:13 pm
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Location: England
I've searched this subject but couldn't find anything that answered my questions.
I'm having a frame built with Columbus Spirit. I like the idea of a seat mast as the bike will only be ridden by me and I don't intend to break it down for travel purposes. I just wondered what weight differences, if any, there are in a steel mast vs a modern lightweight post? Also, being steel, would there be a comfort benefit with the mast?
Any help or experience much appreciated.


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PostPosted: Wed Jan 23, 2013 2:42 pm 
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Location: England
My frame will be 61cm.


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Posted: Wed Jan 23, 2013 2:42 pm 


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PostPosted: Wed Jan 23, 2013 3:41 pm 
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Here were the results of road vibration tests performed @ MIT on Cervelo frames which were essentially equivalent except for material type: steel, Al, or carbon fiber. The Al transmitted a bit more vibration than the other two at certain frequencies, but not dramatically so:

Image

The downside of steel would be the additional mass. With carbon ISP versus conventional Al or C post is fairly close. So I'd believe steel ISP would be heavier than Al post. I can't be certain of that, however.

Here's results from a VeloNews test on posts. They also found Al transmitted a bit more vibration than C (slightly, among other factors). Presumably steel would be close to carbon:

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PostPosted: Wed Jan 23, 2013 4:57 pm 
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Hmm, I'm no egg-spert, but I didn't think most modern round steel tubes were designed to be 'masted', because the walls are so thin (a standard Spirit seat tube is only 0.6mm thick at the top end: http://www.columbustubi.com/eng/4_4_2.htm" onclick="window.open(this.href);return false; ), however, it's obviously being done. I wonder if they use custom-drawn tubes with a thicker section for the mast, or do they just shove a regular post all the way down past the top tube, as per usual? Interesting.

Personally, I wouldn't like to have a "post" with 0.6mm walls, even if it was steel. Steel is obviously a lot stronger than alu, but many alu post walls are ~3.5mm-thick at the high-stress areas for a reason


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PostPosted: Wed Jan 23, 2013 6:25 pm 
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Location: England
Thanks.
Interesting on the seat post tests.
Although I'm no expert, I'm personally not worried about a steel mast regards it's strength. I've certainly not read or seen anything which would give cause for concern. Some of the English frames have pretty long seat masts.
I guess I could try and get my builder to weigh the addition tube.


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PostPosted: Wed Jan 23, 2013 10:29 pm 
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If you're not hopping on that seat mast (aka racing cross) I don't *think* you'll have a problem.

I've seen a pic one frame that someone landed on and the seatmast bent backwards, so IMO cross + steel seatmast = bad idea.

...but I'm not expert. I'd wander over to Velocipede Salon and ask there too. Lots smarter people than I am hang out there.

HTH

M


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PostPosted: Thu Jan 24, 2013 12:14 am 
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I love how this rides and yes of course it would be lighter with a carbon or lightweight post but this is so much sexier.

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PostPosted: Thu Jan 24, 2013 4:56 am 
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Is this mast wider than the rest of the seat tube, or is it an illusion created by the shadow under the top of the seat stay?

Image


Last edited by User Name on Thu Jan 24, 2013 6:13 am, edited 3 times in total.

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PostPosted: Thu Jan 24, 2013 5:02 am 
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gummee wrote:
I've seen a pic one frame that someone landed on and the seatmast bent backwards, so IMO cross + steel seatmast = bad idea.
That's not surprising; it's pretty thin stuff. I bet if someone made a steel seatpost, the walls would be way thicker than 0.6mm, even it was a 'bling' one for the high-end market.
My Ultra Foco Cervelo Superprodigy has just cracked for the second time (in 8 years) at the seat tube/seat stay/top tube juncture, and it obviously has a standard seatpost set-up. I used to have a had habit of slamming back down on the saddle after a standing effort, which might've caused the first crack, but I'm not sure about the 2nd one.


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PostPosted: Thu Jan 24, 2013 6:28 am 
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It's extremely unlikely a skilled frame builder would use 0.6mm tubing for the seat tube collar. Or the cluster, for that matter.

User Name -- that looks like a shadow. Nothing on the rest of that frame possibly indicates any necessity for a wider mast.

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PostPosted: Thu Jan 24, 2013 7:42 am 
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elviento wrote:
Nothing on the rest of that frame possibly indicates any necessity for a wider mast.

It probably is wider - steel ISPs necessitate the joining of two steel tubes to make the ISP long enough. That's why you don't see many of them, and why there's always* a join involved somehow.

* Sacha White (of Speedvagen / Vanilla) I believe has custom steel tubes made for his ISPs, but I also think the difficulty / cost / complication / limited supply could be part of the reason he is now offering a carbon ISP option.


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PostPosted: Thu Jan 24, 2013 9:36 am 
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That's interesting. Can't they just order a longer tube?

BTW, dug up another pic...


Attachments:
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nahbs_day2_z_33.jpg [ 79.49 KiB | Viewed 1642 times ]

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PostPosted: Thu Jan 24, 2013 9:47 am 
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Not that simple (or cheap) as I understand it - which is why, as I say, Speedvagen / Vanilla tubes are custom and most others don't bother.

It is also a heavier option on steel which removes another benefit of doing it on Ti, Alu & carbon.


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PostPosted: Thu Jan 24, 2013 10:41 am 
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I don't know if my steel seat mast is lighter than an aluminum or carbon seatpost, but it is beautiful and I love the ride feel.

http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=79009&hilit=custom+steel

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Posted: Thu Jan 24, 2013 10:41 am 


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PostPosted: Thu Jan 24, 2013 3:59 pm 
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I think more of a big deal is being made of this than it really is...

Any builder can do it and any builder worth a damn will have no problem doing it without a lot of weight penalty versus adding a binder bolt and clamp for a carbon post...

The steel seat tube can be fairly thin walled and not a massive weight penalty with a reasonably light topper.


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