Classic & Vintage - 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".

...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".

1.25 inches into the frame? It sounds like you have one of the older model seat posts, where the riders would ride on huge frames and seat post length doesn't really matter. I would honestly give it 2 inches instead of 1.25, as I have seen people put in about that much into their frame, and the paint start chipping off of the seat tube from the seat post adding pressure from the inside. But, I know little of bikes in general.

So, is about 1 1/4" enough insertion for safety?

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:

http://www.retrobike.co.uk/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=60375&g2_serialNumber=4

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.

I've always prefered 1" past the bottom edge of the lug or top tube.

4" MIN - but I am a BIG guy.

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.

Five inches sounds awfully short, even for the Campy "shorty". Sounds as though the post was altered. Too short, IMO.

Just the tip?

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.

FBinNY on the mechanics forum once put up on there
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.

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.:o

five inches sounds awfully short, too short, imo.

twss

Five inches sounds awfully short, even for the
Campy "shorty". Sounds as though the post was altered. Too short, IMO.

To say that five inches is too short....is just very hurtful.:(

The tightness of the clamp is a factor too. ;)

Ah ...the innuendo. You guyz' minds are in the gutter. ;)

There's a spot. You'll know when you find it. ;)

The tightness of the clamp is a factor too. ;)

:roflmao2:roflmao2::roflmao2::roflmao2:

dirty old men.

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.

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.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/1938%20eBay%20Paramount/CampyNRSeatpost.jpg

this topic went south fast...

http://yourmotivational.com/uploads/9415.jpg

:eek:

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.

Most seat tubes are single butted with the butted end at the BB shell. Columbus Spirit for Lugs is fairly typical, and has a 150mm butt and a 40mm transition taper.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/Tubing/spiritforlugsseattube.jpg

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.

this reply, ftw.

How does riding style affect the amount of stress at this joint? Aggressive riders put less weight on the seat than casual riders, right?

Depends on what you mean by aggressive. I'm pretty sure these guys stress their seatposts WAY more than I do on my road bike.

http://1.bp.blogspot.com/_eVfX78AkyGo/S9bqv4Wpt_I/AAAAAAAAAdA/TW-FF7y73Qk/s1600/20090328_TRACK_WORLDS_D4_WHEELIE_SPRINT.JPG.jpeg

BMX jumpers/freestylers only sit down between runs so they can get by with 78mm seatposts:

http://www.danscomp.com/products-PARTS-SEATPOSTFORRAILS/472061/Fit_Down_Low_Seat_Post.html

[QUOTE][

noglider

How does riding style affect the amount of stress at this joint? Aggressive riders put less weight on the seat than casual riders, right?
/QUOTE]

I think what noglider is trying to say is;" it's not the size of the post that matters, it's how you use it".

Thanks for the info and laughs. Here's a pic of the post next to a standard length one. I don't know why they made the flutes so long. They'll just end up in the seat lug. Looks like I'll have to pass the post on or buy a frame 4 cm larger than I need.

http://i40.tinypic.com/24quujk.jpg

BTW: I know the clamps on the short one are in the wrong position. Someone was gonna point that out!

the deeper you stick it in the seat tube, the better. for you, and your ride.

I'll bet your post was hacked shorter to save weight. However, it appears there is no way to insert it far enough (i.e., below the bottom of the TT) without also having the flutes below the top of the seat tube. This may allow water to collect in the seat tube, and, potentially, lead to a stuck seat post. Thus, if you do end up using this ribbed post, before you put it in the hole I strongly recommend you lube the shaft...errr, I mean, grease the post...uhh, never mind.

That seat post needs to start a new life as a paper weight.

"I'll bet your post was hacked shorter to save weight." - and/or those flutes may have been cut "aftermarket", notice the different shape at the ends of the flutes. These were milled with a ball-nose endmill while the "factory" flutes were milled with a saw. Also note how close to the "patent' engraving they are. I'd put that pic in the "drillium - dos and donts" thread.