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PostPosted: Wed Apr 06, 2011 3:31 am 
BoTM Winner / PoTM Winner
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GoldenEraMTB wrote:
pete_mcc wrote:
Forgot to say, GoldenEra, I am pretty sure that Henrik Djernis won one or two of his world champs on a Ritchey with an extended seat tube like that Empella so that he could reduce the weight of the bike.


Did not know that, thanks. I'll have to look around for a photo of that.



photo credit to veloculture(I think that's who I stole it from) on the VRC forum. there's a few more I'm having trouble finding

Image

MikeD wrote:
I like the Empella's novelty. The "weight saving" argument doesn't really work on a steel frame, the extra tube weighs more than a post would (especially as it's got the heavy part of a post still in it) :) Makes for an endearingly unusual frame, though.


false.

except for the last sentence


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PostPosted: Wed Apr 06, 2011 7:00 am 
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Bontrager OR 95/96


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 Post subject:
PostPosted: Wed Apr 06, 2011 10:38 am 
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Quote:
false.


OK, you made me think about it :)

250mm length of 28.6mm OD 0.5mm wall steel tube = about 80g.
300mm length of 27.2mm OD 1.mm wall alu tube = about 70g.

You need a seat clamp either way, so it's only the weight of the actual seatpost tubing that counts, but you need a bit more of it to go inside the frame. I'm thinking it's marginal at best, although I may well have either neglected something fundamental or done the sums wrong ;)

A seat-mast Ritchey would be a nice thing to have either way.


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 Post subject:
PostPosted: Wed Apr 06, 2011 11:16 am 
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MikeD wrote:
250mm length of 28.6mm OD 0.5mm wall steel tube = about 80g.

250 x 28.6 x 0.5 x pi x .008 = 89.8g

(the density of steel is typically about 8g/cm3 or 8mg/mm3)

Quote:
300mm length of 27.2mm OD 1.mm wall alu tube = about 70g.

I think you're underestimating the thickness of a typical seatpost wall.

If you compare the weights of different Thomson Elite seatposts from Weight Weenies the mass of a 27.2mm post (ignoring the clamp) looks to be about 6.5g/cm, or about 160g for the equivalent 250mm seat mast.

That's not a huge amount, but if you've already cut down your handlebar, inflated your latex tubes with helium and replaced all your titanium bolts with ZiCrAl...


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 Post subject:
PostPosted: Wed Apr 06, 2011 3:36 pm 
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Aha, rounding error in my rough-and-ready "volume of OD cylinder - volume of ID cylinder" arithmetic. Yes, more like 90g for the steel.

The wall thickness of the post is based on the Race Face XY that happened to be handy :) I'll have to go and look at some others now...


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 Post subject:
PostPosted: Wed Apr 06, 2011 4:29 pm 
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hollister wrote:
GoldenEraMTB wrote:
pete_mcc wrote:
Forgot to say, GoldenEra, I am pretty sure that Henrik Djernis won one or two of his world champs on a Ritchey with an extended seat tube like that Empella so that he could reduce the weight of the bike.


Did not know that, thanks. I'll have to look around for a photo of that.



photo credit to veloculture(I think that's who I stole it from) on the VRC forum. there's a few more I'm having trouble finding

Image


there it is; cool, thanks. Now I have to share a photo with you; check your messages later today 8)
So, the weight savings comes in cutting down the seat tube to an itty bitty thing? Why not just make it with a minimalistic seat clamp attached to the top? Get rid of the seat post, all together.


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 Post subject:
PostPosted: Wed Apr 06, 2011 4:46 pm 
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That's pretty much what modern interpretations do - a seat clamp that slides over the outside of the mast and clamps on like a seat binder.


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 Post subject:
PostPosted: Wed Apr 06, 2011 6:07 pm 
Ain't no party like an S Club party
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So...



Back to the entries and time to make another 'post' in the 'Retro MTB Chat' section then is it...??



BB


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 Post subject:
PostPosted: Wed Apr 06, 2011 6:33 pm 
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BoyBurning wrote:
So...



Back to the entries and time to make another 'post' in the 'Retro MTB Chat' section then is it...??



BB


It was relevant to one of the entries. Did you miss stumpjumper's entry?


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 Post subject: botm april 11
PostPosted: Wed Apr 06, 2011 8:22 pm 
PoTM Winner / retrobike rider
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some great entries so far this month
like the potts

kirbdug :D


Last edited by kirbdug on Sat Apr 09, 2011 3:45 pm, edited 4 times in total.

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