Columbia Seat tube diameter ?

[ozzie]

If you had to use a shim with a 13/16 Schwinn post, the correct size is probably 21.15mm AKA .833". I have one bike that uses this. I am using an aftermarket Schwinn-type 13/16" x 5/8" seat post with a Wald shim.

It is a nearly impossible size to get, and is often said to be interchangeable with 13/16", but is not. Even Sheldon Brown screwed the pooch on this issue, acknowledging 21.15mm's existence in one place, and listing it as the same as 13/16" in others.

I can't be sure but I believe the correct Columbia shim may be slightly thicker than the one i used. The shim I used came with a cheap 21.1 bmx stem and allowed you to fit in a 22.2 or 7/8 ID fork. Hopefully a Columbia expert could confirm.

 

[Superman1984]

If you had to use a shim with a 13/16 Schwinn post, the correct size is probably 21.15mm AKA .833". I have one bike that uses this. I am using an aftermarket Schwinn-type 13/16" x 5/8" seat post with a Wald shim.

It is a nearly impossible size to get, and is often said to be interchangeable with 13/16", but is not. Even Sheldon Brown screwed the pooch on this issue, acknowledging 21.15mm's existence in one place, and listing it as the same as 13/16" in others.

I think it measured exactly that going from the actual post thickness or like 21.18mm. So you're Right

As stated I have the post in that Firebolt frame, 1 in the '51 frame, and I believe 1 or 2 more from other bikes that will fit the seat tubes but I'm Really wanting to position the seat back a little further.
Hell Not even 6" but jus' a little. Height is perfect as I like to be flat foot at stops.

I have been half tempted to tube notch & weld 2 seat posts together but I'd hate to bend the seat tube on the frame or worse snap them after welding; being around 160-180 lbs.

 

[Ernbar]

Super check with mac91xx. He may be able to help you.

 

[bloo]

I can't be sure but I believe the correct Columbia shim may be slightly thicker than the one i used. The shim I used came with a cheap 21.1 bmx stem and allowed you to fit in a 22.2 or 7/8 ID fork. Hopefully a Columbia expert could confirm.

The Wald shim I used was intended for that same purpose, a stem. I don't know what Columbia used, but I'll bet it wasn't a shim. I imagine they had a seatpost that actually fit.

 

[ozzie]

Super check with mac91xx. He may be able to help you.

@Ernbar, can you check if your beautiful recent Columbia aquisition has a shim. If not can you measure the OD of the post. I would have bought that bike of yours in a heartbeat if I could have got it packed and sent here.

 

[Superman1984]

Super check with mac91xx. He may be able to help you.

Thanks. I'll send him a message. The things we go through to get these bikes either back to original/period correctness & or to customize them huh We Really are Addicts & a touch Crazy with Madness

 

[bloo]

I think it measured exactly that going from the actual post thickness or like 21.18mm. So you're Right

As stated I have the post in that Firebolt frame, 1 in the '51 frame, and I believe 1 or 2 more from other bikes that will fit the seat tubes but I'm Really wanting to position the seat back a little further.
Hell Not even 6" but jus' a little. Height is perfect as I like to be flat foot at stops.

I have been half tempted to tube notch & weld 2 seat posts together but I'd hate to bend the seat tube on the frame or worse snap them after welding; being around 160-180 lbs.

I imagine that lucky 7 seatposts must exist in that size, but I have never seen one. The seatpost I am using in my 21.15 bike is an extra long solid aluminum straight one, in the interest of strength.

They do make laid back seatposts, BMX style, in 13/16" that you could use with a shim. I always expect those laid back ones to just bend but solid alloy versions are available, as well as some made out of CR-MO tubing. Either of those should be stronger that the typical ones.

I hate the shim. The first thing it did was slip and scraped the crap out of my new seatpost. It's holding now.

 

[Ernbar]

@Ernbar, can you check if your beautiful recent Columbia aquisition has a shim. If not can you measure the OD of the post. I would have bought that bike of yours in a heartbeat if I could have got it packed and sent here.

Yea she is a beauty indeed and a sweet rider. The post is 5/8. Mac 91cut me a post to raise the seat a bit more.

 

[Superman1984]

I imagine that lucky 7 seatposts must exist in that size, but I have never seen one. The seatpost I am using in my 21.15 bike is an extra long solid aluminum straight one, in the interest of strength.

They do make laid back seatposts, BMX style, in 13/16" that you could use with a shim. I always expect those laid back ones to just bend but solid alloy versions are available, as well as some made out of CR-MO tubing. Either of those should be stronger that the typical ones.

I hate the shim. The first thing it did was slip and scraped the crap out of my new seatpost. It's holding now.

Yeah I have heard tales of those generic bmx style with & without the braces just folding over. When it comes to steel I can weld & gusset since it'd be 90° but I'm kinda not keen on that look for this bike.

I had that happen before with a polished aluminum post I cleaned after it had corroded some inside the steel frame; I cussed like a sailor, pulled it out, kicked the bike over, & then proceeded to repolish to very carefully try again before tightening the bolt to Superman status I pity the fool who had to readjust that seat

 

[ozzie]

Yea she is a beauty indeed and a sweet rider. The post is 5/8. Mac 91cut me a post to raise the seat a bit more.

Is it 5/8 at the top or where it slips into the frame?