Seat post minimal insertion...

Discuss light weight issues concerning road bikes & parts.
audiojan
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Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

I'm building up a new bike with Record EPS and want to mount the v2 power unit in the seat tube. The bottle cage bosses on the inside of the frame is sticking out JUST far enough that I can't get the battery passed them. So, the option I have is to have the battery on top of the bottle cages, which gives me about 10-11cm of seat post length in the frame. Is that enough? The frame is a NeilPryde Bura SL btw. The min. insertion for the seat post is marked as 85mm, so I'm passed that.
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

ToffieBoi
Posts: 357
Joined: Fri Jan 31, 2014 4:54 pm

by ToffieBoi

Min insertion written on the post is mostly enough. But to me sure, a few cm more is a better idea. So in your case, 10.5cm is quite good.
Since you can have 11cm inside the frame, I believe it is enough.

bricky21
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Joined: Tue Sep 14, 2010 3:28 pm

by bricky21

I like to use the seat stays as a guide along with the minimum insertion recommendation on the seat post. If minimum insertion of the post does not extend past the bottom of the seat stays by at least a centimeter then it isn't long enough.

audiojan
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Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

The seat stays on the Bura are pretty far down, so I doubt that's a good guide to use… That would mean a VERY long seat post for pretty much everyone….

I've contacted NP and they're looking into it. First look, it's ok and safe. I'll keep WW community up to date with my progress. (and yes, photos ones it's done and built!)
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

Butcher
Shop Owner
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Joined: Sun Jan 03, 2010 4:58 am

by Butcher

Nice to see you stepped up the v2 power unit. So much better not seeing stuff like that hanging off the bike.

audiojan
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Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

Butcher wrote:Nice to see you stepped up the v2 power unit. So much better not seeing stuff like that hanging off the bike.


The v1 power unit is just to big that it's difficult to mount it on a frame without the bosses on the underside of the down tube by the BB… anything else interferes with either the tire (mounted on the chain stay) or the second bottle cage (mounted on the bottle cage mounting bracket).

If I could shave about 1mm from the bottle cage bosses inside of the frame, this would fit perfect! Not easy to reach though… :noidea:
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

Camilo
Posts: 361
Joined: Sun Mar 23, 2008 7:31 pm

by Camilo

How about removing the bottle cage bosses and either forgoing the seat tube water bottle or wrap something grippy (piece of inner tube) around the seat tube at that point, and using zip ties to attach the water bottle cage. Good strong zip ties with something to keep them from slipping down the tube would work fine I think.

As for me, whenever I want to know what the minimum insertion is if I want to cut off a seat post, I just measure from the bottom up to the line, and mark a new line the same distance up from the shortened post.

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Max Gravity
Posts: 534
Joined: Sat May 26, 2007 11:57 am

by Max Gravity

I would remove the rivet nuts and make 2 bolts from rounded washers with a welded on stud bolt.
(glued from the inside)

[img][img][/img][/img]

edit: what the heck happened to the upload img function??
Max Gravity, unfairly treated by gravity!

audiojan
Posts: 778
Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

:evil: Really wish the image upload worked. This sounds like a good idea. But how the heck do I ever reach the rivet nuts? It's pretty far down in the seat tube. I guess I could drill them out, but that doesn't sound very comforting either… Plus then I still need to glue the washer in way down there...
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

Butcher
Shop Owner
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Joined: Sun Jan 03, 2010 4:58 am

by Butcher

I had the same issue when I was building my rain bike. My answer was to replace the frame. I thought that was the best idea when I saw the big crack on the right chain stay.

The insurance company was not to happy paying me more money to buy a frame. I was ok with that. Solved my problem with installing the v2 power unit.

RussellS
Posts: 724
Joined: Wed Feb 03, 2010 1:31 am

by RussellS

As for how far to insert a seatpost into the seattube, 10-11cm is more than far enough. Way more than enough. I rode a bike with a carbon post that was only about 3 inches into the seattube. 3 inches from the top of the seattube. Worked just fine. Carbon bike frame and carbon post.

audiojan
Posts: 778
Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

Replacing the frame is not an option. I'm really looking forward to riding the NP Bura SL this year.

RussellS, thanks for the input. Preliminary info from NP is that it's ok. They're looking into it further. Meanwhile, I've gotten everything built except the crank set install, still waiting for my Q-rings to arrive (been using Q-rings on all my bikes for years, so no reason to swap now).
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

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btompkins0112
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by btompkins0112

What would the seat stays matter?? The pressure is going to be to the front of the seat tube, so the top tube junction is what you want to extend past.

audiojan
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Joined: Fri Jan 27, 2006 1:38 pm
Location: New Hampshire

by audiojan

The seat post is well past the top tube intersection. Heck, by now, I'm just going to cut the post and hope for the best.
"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

5 8 5
Posts: 1353
Joined: Sat Jul 29, 2006 2:36 am
Location: UK

by 5 8 5

btompkins0112 wrote:What would the seat stays matter?? The pressure is going to be to the front of the seat tube, so the top tube junction is what you want to extend past.

bricky21 wrote:I like to use the seat stays as a guide along with the minimum insertion recommendation on the seat post. If minimum insertion of the post does not extend past the bottom of the seat stays by at least a centimeter then it isn't long enough.

Certainly the case with steel, aluminium and titanium frames it's prudent to have the seatpost extend beyond the seatstay junction due to the stresses that can be inflicted which can lead to frames cracking.

It's different with carbon frames though. I've seen quite a few carbon frames where the actual seatpost fit diameter doesn't actually extend that far down the seat tube. A big part of a long seatpost can effectively be in fresh air, doing nothing.

10-11cm should be plenty. Neil Pryde should clearly state a minimum insert length if it's very different from the norm.

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