So, how deep do I really have to insert it?
11-08-11, 01:48 AM
#1
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So, how deep do I really have to insert it?
...considering I only have about five inches? Wait, let me start that again!
I have a short, fluted NR seatpost with no minimum insertion mark. The post is a little over five inches long and if I insert it more than an inch and a quarter into the frame, the flutes start to disappear. Plus, I need a little less than four inches to get proper saddle height. So, is about 1 1/4" enough insertion for safety? I really don't want to have my rear wheel inserted into a part of my anatomy I consider "exit only".
I have a short, fluted NR seatpost with no minimum insertion mark. The post is a little over five inches long and if I insert it more than an inch and a quarter into the frame, the flutes start to disappear. Plus, I need a little less than four inches to get proper saddle height. So, is about 1 1/4" enough insertion for safety? I really don't want to have my rear wheel inserted into a part of my anatomy I consider "exit only".
11-08-11, 02:06 AM
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...considering I only have about five inches? Wait, let me start that again!
I have a short, fluted NR seatpost with no minimum insertion mark. The post is a little over five inches long and if I insert it more than an inch and a quarter into the frame, the flutes start to disappear. Plus, I need a little less than four inches to get proper saddle height. So, is about 1 1/4" enough insertion for safety? I really don't want to have my rear wheel inserted into a part of my anatomy I consider "exit only".
I have a short, fluted NR seatpost with no minimum insertion mark. The post is a little over five inches long and if I insert it more than an inch and a quarter into the frame, the flutes start to disappear. Plus, I need a little less than four inches to get proper saddle height. So, is about 1 1/4" enough insertion for safety? I really don't want to have my rear wheel inserted into a part of my anatomy I consider "exit only".
11-08-11, 02:24 AM
#3
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I don't like that number, but on my Pinarello it is just enough to match someone else's idea of absolute minimum insertion, which is just so the bottom of the seatpost goes a little bit past the bottom of the top tube.
I'd get a longer post, personally. I'm rather fond of my Pinarello's seatcluster as well as having an intact posterior, so I've got a long MTB post practically hitting the bottle cage braze-on. I might risk the 1.25" if I was 115 lbs. and a dainty pedaler.
Oh, I should note that to get that 1.25" measurement to be below the top tube I have to measure from the dip in the side of the seat lug:
I'd get a longer post, personally. I'm rather fond of my Pinarello's seatcluster as well as having an intact posterior, so I've got a long MTB post practically hitting the bottle cage braze-on. I might risk the 1.25" if I was 115 lbs. and a dainty pedaler.
Oh, I should note that to get that 1.25" measurement to be below the top tube I have to measure from the dip in the side of the seat lug:
Last edited by LesterOfPuppets; 11-08-11 at 02:29 AM.
11-08-11, 02:39 AM
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One and a quarter inches is not enough to ensure proper strength. To that, add this...
How much do you weigh and are you an aggressive rider? Both of those factors will impact how little, of the seat post, goes into the fit.
Also, what kind of bike are we talking about? A high ender, with exotic tubing, will want more insertion to ensure safety to, both, the rider and the machine.
Your best bet is to get a proper seat post and be done with it. Weigh the cost against the risk and decide.
How much do you weigh and are you an aggressive rider? Both of those factors will impact how little, of the seat post, goes into the fit.
Also, what kind of bike are we talking about? A high ender, with exotic tubing, will want more insertion to ensure safety to, both, the rider and the machine.
Your best bet is to get a proper seat post and be done with it. Weigh the cost against the risk and decide.
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11-08-11, 06:35 AM
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I always use the four finger measurement, which is what the min insertion marks are close to on modern post, of course every bodies hands are at different widths but it should be close.
11-08-11, 06:45 AM
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Five inches sounds awfully short, even for the Campy "shorty". Sounds as though the post was altered. Too short, IMO.
11-08-11, 08:40 AM
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If you keep on trying to insert it and taking it out again, you are gonna wind up with more bikes than you can handle.
11-08-11, 08:49 AM
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FBinNY on the mechanics forum once put up on there
the best explanation of this I've seen:
Thus, the post has to go in far enough to prevent your body
weight from camming it in the lug and tube. Everything else
is pretty much immaterial. It must extend below the TT far
enough that the joint stresses there don't **** up your frame.
This varies from frame to frame, depending on construction,
materials, and design.
Personally, as a confirmed fat ass, I try to make certain I've
got at least a couple of inches down in there where it does me
some good.......just like in your other reference.
the best explanation of this I've seen:
Twenty to one it was caused by a seatpost not inserted deep enough into the frame.
The minimum insertion marks reference the minimum insertion for the seat post not to cam out of the seat tube. But that's only one half of the equation. On designs like this one where the seat tube extends beyond the top the post must extend to a depth of about one inch below the bottom of the top tube, which is usually beyond the seat post's mark.
A post inserted only to the 2.5" minimum mark will end above the top tube, or very close to that creating a major stress concentration right at the weld, which is the worst possible scenario.
Your good luck is you spotted it before it let go completely with seri-ass consequences.
Step one if you want to keep the frame, get a seat post that extends at least 3" below the crack, so it carries your weight well below the damaged area and transfers the load to the frame. Next use JB weld, or epoxy and a piece of fiberglass to reinforce the crack and prevent it's spreading and you should be OK, but keep an eye on it. It doesn't have to be a super strong repair since now the extended tube's only function is to support the clamp.
The minimum insertion marks reference the minimum insertion for the seat post not to cam out of the seat tube. But that's only one half of the equation. On designs like this one where the seat tube extends beyond the top the post must extend to a depth of about one inch below the bottom of the top tube, which is usually beyond the seat post's mark.
A post inserted only to the 2.5" minimum mark will end above the top tube, or very close to that creating a major stress concentration right at the weld, which is the worst possible scenario.
Your good luck is you spotted it before it let go completely with seri-ass consequences.
Step one if you want to keep the frame, get a seat post that extends at least 3" below the crack, so it carries your weight well below the damaged area and transfers the load to the frame. Next use JB weld, or epoxy and a piece of fiberglass to reinforce the crack and prevent it's spreading and you should be OK, but keep an eye on it. It doesn't have to be a super strong repair since now the extended tube's only function is to support the clamp.
weight from camming it in the lug and tube. Everything else
is pretty much immaterial. It must extend below the TT far
enough that the joint stresses there don't **** up your frame.
This varies from frame to frame, depending on construction,
materials, and design.
Personally, as a confirmed fat ass, I try to make certain I've
got at least a couple of inches down in there where it does me
some good.......just like in your other reference.
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11-08-11, 08:50 AM
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11-08-11, 09:54 AM
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roflmao2:
11-08-11, 11:42 AM
#19
Senior Member
With db tubing, how far down the seat tube does it thin out?
I agree with others that a longer seatpost seems prudent. You might also ask this question at the framebuilders sf.
I agree with others that a longer seatpost seems prudent. You might also ask this question at the framebuilders sf.
11-08-11, 11:45 AM
#20
Decrepit Member
Here's my vintage 180mm Nuovo Record "long" seatpost. The minimum insertion line is 2.25" from the end of the post. According to Catalog 16 (1968), two lengths were available. The "standard" length was 130mm and the "long" length was 180mm. I suspect the OP has the 130mm standard length post, but personally, I'd make sure at least 2.25" of the post was inserted into the seat tube.
11-08-11, 11:58 AM
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11-08-11, 12:05 PM
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11-08-11, 12:06 PM
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11-08-11, 12:42 PM
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How does riding style affect the amount of stress at this joint? Aggressive riders put less weight on the seat than casual riders, right?
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