Custom steel ISP vs standard seat post. Weight & comfort.

Discuss light weight issues concerning road bikes & parts.
MDH
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Location: England

by MDH

Both English frames/bikes are great.

by Weenie


MDH
Posts: 47
Joined: Sun Jun 05, 2011 10:13 pm
Location: England

by MDH

CharlesM- Any idea on the weight difference? A few hundred grammes?

xnavalav8r
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by xnavalav8r

Seeing this bike, one thought immediately came to mind... if Hugh Heffner and one of his Playmate wives were bicycles, this is what the offspring would look like. A mix of very old and very new. Frankly, I like it... except the fork. I prefer a straight-blade fork.

Now back to the topic...

CharlesM wrote:Image

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CharlesM
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by CharlesM

MDH wrote:CharlesM- Any idea on the weight difference? A few hundred grammes?


No... I've held a cut piece of tubing and the diffs for a given length of high end steel tubing is not double the weight of the appropriate length carbon...

Remember that an ISP doesn't have a big overlap of materials like a standard seat post that gets pushed into a frame will have. And most carbon seat posts are built with fairly thick walls to fight being crushed.


So an ISP will be the weight of the tube length and the mast topper. Fairwheel have mast toppers at and below 100 grams. The steel seat tube for the ISP will depend a lot on the geometry, but a full length tube that is 25 inches of ms2 straight gauge steel tubing (28.6mm) weighs 340 grams. That's only 13.4 grams per inch and most folks will only have what, 5-6-7 inches? 80 grams for a 6 inch ISP... Thats an ISP weight some place near 180 grams plus or minus...


For a traditional seat post you'll have the seat post it's self, including the saddle mounting hardware and that will likely be near 200 grams. You'll also have the seat post clamp and bolt that for steel is going to weigh 10-20 grams...

This is just generally speaking and people can tune both things, but I would bet the seat post versus ISP difference would be damn near nothing for most folks. Certainly not a couple of hundred grams.

MDH
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Location: England

by MDH

Could you be a bit more specific?

MDH
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by MDH

Just kidding!

Thanks very much for that. Very informative. Food for thought.

mattydubs
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Location: Denver

by mattydubs

CharlesM wrote:
No... I've held a cut piece of tubing and the diffs for a given length of high end steel tubing is not double the weight of the appropriate length carbon...

Remember that an ISP doesn't have a big overlap of materials like a standard seat post that gets pushed into a frame will have. And most carbon seat posts are built with fairly thick walls to fight being crushed.


So an ISP will be the weight of the tube length and the mast topper. Fairwheel have mast toppers at and below 100 grams. The steel seat tube for the ISP will depend a lot on the geometry, but a full length tube that is 25 inches of ms2 straight gauge steel tubing (28.6mm) weighs 340 grams. That's only 13.4 grams per inch and most folks will only have what, 5-6-7 inches? 80 grams for a 6 inch ISP... Thats an ISP weight some place near 180 grams plus or minus...


For a traditional seat post you'll have the seat post it's self, including the saddle mounting hardware and that will likely be near 200 grams. You'll also have the seat post clamp and bolt that for steel is going to weigh 10-20 grams...

This is just generally speaking and people can tune both things, but I would bet the seat post versus ISP difference would be damn near nothing for most folks. Certainly not a couple of hundred grams.


I had this same debate with myself. I have a custom frame built from Columbus Spirit and my builder thought it would be better to just cut a seatpost short given my other desires: I wanted a pretty traditional style "parallel to the ground" top tube and the ability to adjust up and down a few MM for different saddles, etc. You can do this with a mast, but a Thomson cut down for the same frame is pretty light (I'll have to weigh it... but FWIW Im using an Elite at the moment cut with just enough in to be safe, debating on setback or 0 setback Masterpiece). It's half an aesthetic thing, which makes it hard.

If in doubt, go with a seatpost. If your frame is going to be more compact (and you need more post as a result) then a mast will probably be lighter.

As for carbon vs ti vs alu... it depends on your cockpit, I guess. With steel I think you don't need as much deflection (though I am debating a setback post) and Thomson (and a few others) make alu posts that are just as light (or lighter). I ended up with a Thomson stem and using the old rule of stem matches bars made it a no-brainer. If you're hellbent on the lightest setup, ignore that rule.

If you get a mast, see if your builder will do an integrated stem/bar... that would be very pretty and rather light.

shimmeD
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by shimmeD

When you can use Smud Carbon in-line seat-post at claimed 95g for a 300x27.2mm (or New Ultimate alloy in-line <150g), std seat-post is the ww way (not discussing ride quality or aesthetics).
I have a cut-down Thomson Elite in-line weighing 134g, to compare.

shimmeD
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by shimmeD

That doesn't read very clearly: I'll expound.

I played out the exact same scenario of to-ISP-or-not, so I cut down my Thomson Elite to about 100mm in anticipation of having an extended seat-tube with normal brazed bolt arrangement. The cut-down seat-post weighs 134g.

Compare these:
carbon seat-post (Smud Carbon) - 95g
steel ISP - +100g & length of extended seat-tube
cut-down Thomson Elite - 134g + extended seat-tube

I've chosen to go standard seat-post and not ISP.
Less is more.

MDH
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Joined: Sun Jun 05, 2011 10:13 pm
Location: England

by MDH

Mine too will be traditional geometry. At 61cm and not throwing my cheque book at the build, it's not going to be super WW. Though both eyes are on the grames.
I prefer the aesthetics of an internal 'post' in a mast vs a cap. But for me, if it's boiling down to purely aesthetics with an ISP then I'm erring towards going with a post. It's seeming like a lot of unnecessary work joining two tubes to make one. Especially given that the likely hood is there'll be a weight penalty.
Last edited by MDH on Fri Jan 25, 2013 9:24 am, edited 2 times in total.

MDH
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by MDH

mattydubs- Any photos of your frame?

MDH
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by MDH

shimmeD- Is yours built? Any photos.

Burgunder
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Joined: Tue Aug 14, 2012 7:36 am

by Burgunder

What about the comfort of ISP vs. seatpost?

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CharlesM
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by CharlesM

Any answer would be a generalization that wont apply to all things...

different seat post types and different tubes used for ISP mean that the answer would need a more detailed question.

by Weenie


MDH
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Joined: Sun Jun 05, 2011 10:13 pm
Location: England

by MDH

Just spoke to the builder. Think I'm going to ditch the ISP idea.

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