the correct seat post size

[cols3064]

can anyone tell me the correct seat post size for reynolds 531 plain gauge tubing

[tooley92]

I'm sure it's 26.8mm

[tatanab]

Agreed 26.8
I've had a couple of plain gauge frames over the years (Claud Butler Olympic Sprint from 60s and early 70s) and they rode very nicely indeed.

[Russell160]

I would say 27.2, just to be contrary. That's what my own 531 takes.
I think the only way to be sure is to take it to a lbs and get them to measure it with a digital Vernier. As I understand there are differences say between a 27 and a 27.2, and I don't think you can measure that sort of difference with naked eye.
Could try same question in bikes and bits, technical forum?

[tooley92]

I would say 27.2, just to be contrary. That's what my own 531 takes.
I think the only way to be sure is to take it to a lbs and get them to measure it with a digital Vernier. As I understand there are differences say between a 27 and a 27.2, and I don't think you can measure that sort of difference with naked eye.
Could try same question in bikes and bits, technical forum?

I suspect that your 531 frame that takes a 27.2mm post will be made from double butted tubing, however I have owned a 531c Harry Hall which took a 27mm post (531c usually 27.2mm) and a 531st Harry Quinn which took a 27.2mm post (531st usually 27mm) so it seems that it depends on who reemed the post hole.

[Russell160]

Fair point, well made, I wasn't aware there were different diameters to different types of 531. I guess it just sort of reinforces my point that there isn't a 'correct' answer,only that you have to measure what you've got.

[mickle]

The external diameter of a steel seat-tube intended to accept a front derailer is always 28.6. The stronger the tubing the thinner the material used and therefore the larger the bore. Japanese ChroMoly was 26.8mm internal diameter, British ChroMoly (501) was 27.0 and ManganeseMoly (531) 27.2. The level of butting (531c, 531st etc) isn't relevant because butting is a process of removing material from the middle of the tube and has no influence on the inner diameter at the upper end of the seat tube.

531 is always 27.2mm. By definition.

[Mick F]

531 is always 27.2mm. By definition.

I'm not too sure about that. 27.2 is the size of my 531c, but I'm positive that I've read on here that it isn't always the case.

[tatanab]

The external diameter of a steel seat-tube intended to accept a front derailer is always 28.6.

True for road frames before frames got fat.

531 is always 27.2mm. By definition.

Not true. 531 was available in a number of different gauges. ST was thicker than C by 0.2mm so takes a smaller diameter saddle pillar. Source of information is the Tony Oliver book.

If it were true that all 531 frames took 27.2 and that the butting is irrelevant to that, then a plain gauge frame would be lighter than a double butted frame because the double butted would be thicker at the butts than a plain gauge is for its whole length. Evidently not the case.

Because of different gauges in use I have had frames in 531, 531C, 531 plain gauge and 531SL which took saddle pillars of 26.8, 27.0 or 27.2 I recall speaking to George Longstaff who was surprised that I had a 27.2 saddlepillar in a frame he had built for 27.0 (531DS)

[mickle]

The external diameter of a steel seat-tube intended to accept a front derailer is always 28.6.

True for road frames before frames got fat. Still true

531 is always 27.2mm. By definition.

Not true. 531 was available in a number of different gauges. ST was thicker than C by 0.2mm so takes a smaller diameter saddle pillar. Source of information is the Tony Oliver book. My old ST frame was 27.2. Go figure.

If it were true that all 531 frames took 27.2 and that the butting is irrelevant to that, then a plain gauge frame would be lighter than a double butted frame because the double butted would be thicker at the butts than a plain gauge is for its whole length. Evidently not the case. Huh? Butting is a process removal of material in the middle of a tube, not addition of material at the ends.

Because of different gauges in use I have had frames in 531, 531C, 531 plain gauge and 531SL which took saddle pillars of 26.8, 27.0 or 27.2 I recall speaking to George Longstaff who was surprised that I had a 27.2 saddlepillar in a frame he had built for 27.0 (531DS)

Eh? You fitted a 27.2 seatpost in a frame designed for 27.0? Impossible. Isn't it obvious that you simply installed a 27.2 post in a 531 frame.

[mickle]

531 is always 27.2mm. By definition.

I'm not too sure about that. 27.2 is the size of my 531c, but I'm positive that I've read on here that it isn't always the case.

Happy to be proved wrong but I've never seen a 531 frame which wasn't 27.2mm.

[tatanab]

Happy to be proved wrong but I've never seen a 531 frame which wasn't 27.2mm.

Make it so - in good humour.

Look at the wall thicknesses in the attached file and it is evident that different sized saddle pillars are used.

http://fivenineclimber.com/bikes/gazell ... lds_80.htm

How did I fit a 27.2 in a 531DS frame meant for 27.0 - well I did not know it was meant for 27.0 and perhaps my saddle pillar was at the lower end of the tolerance, and I'm used to snug fitting saddle pillars. From my talk with George Longstaff I conclude that my DS frame includes an ST seat tube.

[mickle]

I stand corrected.

[pablito]

I have a french built 531 frame (constuit avec Reynolds 531). The existing seat post is some sort of plastic (nylon?) and marked 26.4mm. It seems to fit well, but is too short, so I'm looking to replace it.

Measuring the seat tube with some verynear callipers, I get 26.4mm, but it is possible that the top of the tube has been slightly compressed. Can anybody tell me with confidence what post size I should get, or how I can accurately measure inside the tube? Thanks.

[BigG]

I have a french built 531 frame (constuit avec Reynolds 531). The existing seat post is some sort of plastic (nylon?) and marked 26.4mm. It seems to fit well, but is too short, so I'm looking to replace it.

Measuring the seat tube with some verynear callipers, I get 26.4mm, but it is possible that the top of the tube has been slightly compressed. Can anybody tell me with confidence what post size I should get, or how I can accurately measure inside the tube? Thanks.

I can't help you; but I can confirm that my Freddie Grubb - resprayed but labelled 531 probably correctly - takes a 26.4 mm seat tube. I suspect that this is because the tubes are plain guage. It dates from the eraly 1970s.