cyclotoine

I have a bike from the very early 1970s (presumed built in about 71/72) made of reynold 531 butted tubes frame, fork and stays. The bike is a 62cm and it appears that a 27.0mm seatpost is the right size. I thought all butted 531 tubesets would be 27.2mm, but it appears I am wrong. I guess reynolds came with different butting configurations for different applications? Sorta like columbus SP vs. SL...

Any thoughts? I'm pretty damn sure on this as a 27.0 post slides in nicely but is snug with no rocking or play even with the binder undone, a 27.2 will not go in under any circumstance.

retyred

Name of bicycle is........?

Charles Wahl

Is your frame custom-made? A builder might have chosen a straight-gauge tube for the seatpost on a largish frame (particularly if rider was heavy or roads rough, and Reynolds supplied those in several gauges. A butted 531 seat tube typically was 21/24 SWG for butt/upper, which is about .81/.55 mm; however straight-gauge was available in just about any gauge.

Antipodes

Corky.

Dr.Deltron

cudak888 

My '61 Paramount runs a 27.0 post. 531, as usual.

-Kurt

cyclotoine

Did the seatpost you are using come from Little Darwin? I.e. corky? That would confirm it is indeed the size I need, just trying to be 100 percent sure.... I'm way to anal as usual.

worst case scenario is I use the 27.0 from my Marinoni Pista and put the horendous zeus post in the Marinoni till I can find a suitable replacement. Ebay is dry ATM.

cudak888 

As a matter of fact, its a good thing you mentioned Corky. The post on my '61 Paramount is from Lotek (or was it Luker?), but the post on my Trek 610 is from Corky.

Surprise, it's a 27.2.

-Kurt

cyclezen

Reynolds 531 butted could have been found in a number of seattube IDs. from 27.2 down to 26.4 and prolly even smaller. I remember my 71 PX10 was 26.4 and my Limongi (76) was Reynolds Superlight 531DB and also is 26.4. 26.8 is very common.
And 27.0 was as common as 27.2 (maybe more...) for Reynolds built in the 70s and even early 80's.

I'm sure there's a source for listing some of the common bikes and seattube sizes...

use what fits best

cyclotoine

Thanks, kurt. I was wondering how I could have screwed this up. I was sure I had the right seatpost size and was a little confused. To be honest I don't know why I was so sure but I can only assume I had confirmed what the seatpost size was sometime in the past. I'll have to hone out the seat tube a little, maybe it's a bit of build-up of primer and such though it looked pretty clean.

CharlesC

When I made frames I would substitute a down tube for the lighter seat tube for frames I made for real heavy riders. Required a smaller diameter seat post.

cudak888 

Have the local shop run the hone through it, and it should be fine. Might have needed it all along.

Curious, what would you have spec'ed for someone 235lbs riding a 59cm frame? Thicker gauge, I'd assume? My '61 Paramount, as I mentioned before, has a slightly thicker seat tube, and I dare say it is one of the reasons I am rather partial to it (not to mention the stiff English-type fork bend).

-Kurt

Grand Bois

Your PX10 had a smaller ID seat tube only because it had a smaller OD. Peugeot and other French builders used metric sized tubesets.

Sheldon's seatpost size database:
https://sheldonbrown.com/seatpost-sizes.html

I was surprised to find that the seatpost for my '74 Raleigh Competition is a 27.0 until I looked at the above reference and found that it's straight guage.