Old seatposts in new frames
 

Sorry the title was vague and this may not be the forum, but it's where I hang out and when I go to mechanics I usually get nothing. Maybe I should go to framebuilders... but I'll give it a shot here.

Say you want a new frame like a surly and you want to use a record 2 bolt seatpost in it. You will notice that the seat tube extends liberally above the TT-ST junction.

http://www.surlybikes.com/frames/ima...t_complete.jpg

Knowing old frames were not like this, would the old seatposts be designed with this in mind (seeing as the lug joint is the stiffest point and the post should extend past it? Now if you were to put this record post in the LHT above and raise it to it's max height you would not have as much post extending past the Tt-st junction. I dare say that bit of seat tube is not so strong and I am wondering if it would be unsafe.

What do you guys think?

Surly sent me a rather useless reply to my inquiry saying the min. is a function of the seatpost. I did ask if there was a minimum amount of post that should be in the frame and they did not answer. I was very displeased with the reply. Obviously I am not worried about this post snapping I'm worried about the frame deforming.

I don't have an answer but if you want to get a bit scared check out page 2 of this thread:

http://bikeforums.net/showthread.php...angster&page=2

I realise thats aluminum and your frame is cromo but I think some of the same principals apply.

That's an interesting question, but I'd wonder why you were running your seat post at max height. That tells me that the frame might be too small or the post too short (and, yes, I know those vintage Campy posts were mighty short).

Neal

Yikes! And he had 6 inches in the frame which is way more than an old campy post has at max height.

Well if I were to get a surly LHT I would have to go with the largest size a 62cm c-t, which my understanding is the top of the TT-ST junction. Since it is slightly sloping I think it's okay and I am sure this frame would be a lot stiffer and my international. I can run a campy seatpost on a 62 c-c bike no problem. I am evening using a super record at max height on a 62cm c-t gazelle. Yes I am pushing the limits of conventional size wisdom but my rule for a traditional frame is: "if I can use a campy record post I can ride it". Anyway that doesn't apply to an LHT and I may just end up buying some other 2 bolt post... but it seems I could use the record (close to max height) which doesn't leave a ton of post in the frame..

I am just really wondering is max height is a function of the seatpost breaking or a combination of that and it popping out of the frame.... I have seen modern seatposts bend with half their length inserted. Have you ever seen a broken 2 bolt shaft? not me. I don't a record seatpost has ever broken, so it's that frame I wonder about.

Okay, I responded to Surly and they replied back. At least 65mm should be in the frame.. a campy 2 bolt has a limit line at 58mm... so there you have it.

if you don't extend past the 'max' mark on the seatpost and the seatpost extends about an inch or more past the bottom of the toptube, you should be fine.
Ideally, there should be an equal length of post extending below the centreline of the toptube as there is from the T-T centreline to the top of the seatcluster/ seatclamp.

That's interesting. So can you get away with losing 7mm of post height? Stick a gel pad on your saddle!

Neal

I just learned that 62cm is the absolute top of the seat tube i.e. no record 2 bolt in the LHT for me...

Oh well.

Okay the way I get around this is running a vintage Campy OR seatpost, while rmost of the road posts are very short the mountains are not - that being said not all roads are short - some of the old world logo 2 bolts are pretty long as well. I must admit it is limiting when you want to run fluted super record or some of the aero posts.

Not so much that I wanted to use campagnolo but just that I wanted to use a 2 bolt record I had on hand (especially because I like the 2 bolt design... not a problem really, I'll just dump the record on ebay and buy a thomson or something.