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.

My frame will be 61cm.

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:



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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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

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.

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

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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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?

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.

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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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.

That's interesting. Can't they just order a longer tube?

BTW, dug up another pic...

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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.

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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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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