Seat tube for ISP
 

I've wanted to build a bike with an ISP. In the little bit of research that I've done, I've seen that most seat post toppers are 34.9mm. Are guys only building ISP with 34.9mm seat tubes? Seems quite large. Ideally, I'd like to use 25.4 or 28.6. I'd assume that straight gauge tubing would be the way to go as well, but having never done it before, I'm really unsure.

So, what tubing should I use, and where would I get the matching seat topper?

Thanks in advance!

Brandon

Small diameter thinner walled steel is not likely to be up to the task of functioning as a seatpost.. You'd probably want to go with at least the diameter that fits the smallest available topper.

Can you just cut a seat post very short instead of using a topper.
It would look much neater and you can get any size you like.

You can extend the seat tube and binder up and then cut a seat post quite short for the same effect. Like this below.

https://cimg3.ibsrv.net/gimg/bikefor...9a6ef6c150.jpg

What's an ISP? And if you do the really long seat tube like that Paul bike you aren't attaching the SS to the thick bit (assuming an externally butted or "bulge" ST which is generally a good idea unless you have a lug or a sleeve around there).

Thanks guys, I have actually decided not to do an ISP. Seems to be too much trouble than it's worth for what I'm trying to do.

There's a reason why the bike frame (in steel at least) has been in it's form for so many decades. Like so many other "improvements" ISPs have had their 15 minutes of fame and we find that they are not all they wish to be. Andy

I made one in 1977, and not too much later I was embarrassed to be seen on it – such a dumb idea. Not that I cared what other people thought (they mostly liked it), but I cared what I thought. (Hey I was 20 years old, gimme a break). So I cut the tube off above the toptube and added a pinchbolt and slit, voilà a bike I could be seen on in public.

"Before":
https://cimg6.ibsrv.net/gimg/bikefor...85b6c211c2.jpg
(there is no "after" pic)

This was the second frame I ever made, serial number BD2 because my fantasy bike company was Ben Dover Cycles. I even made decals.

In addition to the ISP, there were no nuts in back of the crown or front of brake bridge – brakes attached to braze-ons – but still adjustable for centering.
Braze-on front derailer too, before Campy made them. Not saying I invented the idea, but this was my own design.
All ideas I later came to regret. That and not folding the spare tubular neatly for the photo. Must have been in a hurry, to go smoke some pot or whatever the kids did back then. (Yes, I regret the hair too in retrospect, but the ladies seemed to like it OK...)

The Art Stump dropouts are not regrettable though, still some of the prettiest ever.

Mark B in Seattle

You had under bb cables? That was pretty rare in '77.

The hair was the way everyone wore their hair back then, so that's excusable. The tire is bad though.

I like the Campy belt buckle. I collected a few various bike branded ones way long ago. Andy