50s lightweight frame - 27.0mm seat post?

[avecReynolds531]

I've tried to read & understand about the variances of seat post sizes in classic steel frames.

So, at the risk of appearing stupid, why would a 50s frame have a 27.0mm seat post? The frame seems a lot lighter than a early 80s 531 (27.2mm)?

I've heard of inverted seat tubes and double butting too: I'd be grateful for the shared knowledge here at this forum.

All advice much appreciated.

Thanks,

Tom

[Brucey]

27.0mm seat pin could mean one of several things

1) wrong size seat pin fitted
2) seat pin fitted to unreamed frame
3) slightly heavier gauge seat tube
4) double butted seat tube
5) seat tube fitted upside down

there were lots of tube options then as now, and that the seat tube is a given gauge is suggestive, but does not prove that other tubes are any given gauge.

Whole frame/fork weight is quite indicative.

cheers

[bgnukem]

FWIW my Dawes has a 27.0 seatpost but is Reynolds 531ST tubing with a 1.0mm/0.7mm/1.0mm seat tube wall thickness.

Given a tube OD of 28.6mm the ID should be 26.6mm (28.6 - 2x1.0mm) at the thicker-walled tube ends so I guess the tube is reamed out to 27.0mm (or slightly over).

Reynolds 531C frames I think usually take a 27.2mm seatpost due to the thinner tube wall (0.8/0.5/0.8mm) although should be 27.0mm I think (28.6 - 2x0.8mm) so again I guess they are reamed out to 27.2mm.

So, as per Brucey's reply, it's possible your frame is thick-walled tubing or has not been reamed out much after brazing.

[Brucey]

many seat tubes are meant to be single butted, so the thinner wall thickness is more usually the relevant one. Also note that the tube specification is often loosely stated as XYX (eg 0.8-0.5-0.8mm) which may be true for the down tube, but not always the seat tube. The seat tube is also the most likely to vary in gauge with frame size.

cheers

[avecReynolds531]

Thank you for the replies & knowledge shared - much appreciated.

I'm curious about it: have ordered a scale, will weigh the frame/fork and post the result.

Looking forward to what the result indicates.

[bgnukem]

many seat tubes are meant to be single butted, so the thinner wall thickness is more usually the relevant one. Also note that the tube specification is often loosely stated as XYX (eg 0.8-0.5-0.8mm) which may be true for the down tube, but not always the seat tube. The seat tube is also the most likely to vary in gauge with frame size.

cheers

Interesting. I'd assumed the seat tube would be double butted, with the thicker wall at the upper end where the top tube and seat stays are attached and the seat clamp acts, as well as at the bottom bracket where there is also a junction of tubes, plus higher stresses.

[avecReynolds531]

many seat tubes are meant to be single butted, so the thinner wall thickness is more usually the relevant one. Also note that the tube specification is often loosely stated as XYX (eg 0.8-0.5-0.8mm) which may be true for the down tube, but not always the seat tube. The seat tube is also the most likely to vary in gauge with frame size.

cheers

Interesting. I'd assumed the seat tube would be double butted, with the thicker wall at the upper end where the top tube and seat stays are attached and the seat clamp acts, as well as at the bottom bracket where there is also a junction of tubes, plus higher stresses.

Thanks for this: it's very interesting and I find myself struggling to keep up with why the seat tube is most likely to vary in gauge with frame size.

I forgot to note another reason for a 27mm seat post: metric in place of imperial - though as the frame was built in London most probably mid to late 1950s - this is likely discounted.

This guide to Columbus tubing (albeit from 1988-89) was useful learning for me: it shows butting and weights across their tubesets: http://equusbicycle.com/bike/columbus/columbuschart.htm

As Brucey stated 'Whole frame/fork weight is quite indicative,' I've now been able to weigh the frame & fork: painted frame is 1875g/ 4.13 pounds, painted fork is 695g/ 1.53 pounds. That's for dimensions of a 22 inch top tube (centre to centre) and 22inch seat tube (centre to top).

I'd be grateful for further forum knowledge & input please - what does the weight of the frame suggest about it's construction?

Thanks,

Tom

[Des49]

This guide to Columbus tubing (albeit from 1988-89) was useful learning for me: it shows butting and weights across their tubesets: http://equusbicycle.com/bike/columbus/columbuschart.htm

That's interesting thanks. Does my SPX racing frame really carry such a weight penalty over SLX? I have frames of each packed up, must weigh them out of interest.

[Brucey]

As Brucey stated 'Whole frame/fork weight is quite indicative,' I've now been able to weigh the frame & fork: painted frame is 1875g/ 4.13 pounds, painted fork is 695g/ 1.53 pounds. That's for dimensions of a 22 inch top tube (centre to centre) and 22inch seat tube (centre to top).

I'd be grateful for further forum knowledge & input please - what does the weight of the frame suggest about it's construction?

this weight frame and fork suggests a fairly lightweight DB tubeset. Put it this way, a later 531C frame in that size would be a few ounces heavier than that, depending on how heavy the BB shell, fork crown, lugs, dropout etc are.

cheers

[avecReynolds531]

This guide to Columbus tubing (albeit from 1988-89) was useful learning for me: it shows butting and weights across their tubesets: http://equusbicycle.com/bike/columbus/columbuschart.htm

That's interesting thanks. Does my SPX racing frame really carry such a weight penalty over SLX? I have frames of each packed up, must weigh them out of interest.

Yes, I found that surprising too: 2325g v 1966g is a difference. I've ridden an Italian SLX frame and loved it but never tried SPX - unlikely for a 52/53cm frame size.

As Brucey stated 'Whole frame/fork weight is quite indicative,' I've now been able to weigh the frame & fork: painted frame is 1875g/ 4.13 pounds, painted fork is 695g/ 1.53 pounds. That's for dimensions of a 22 inch top tube (centre to centre) and 22inch seat tube (centre to top).

I'd be grateful for further forum knowledge & input please - what does the weight of the frame suggest about it's construction?

this weight frame and fork suggests a fairly lightweight DB tubeset. Put it this way, a later 531C frame in that size would be a few ounces heavier than that, depending on how heavy the BB shell, fork crown, lugs, dropout etc are.

cheers

Thanks for the 531C context. The lugs on the frame are very finely filed and thin, the pencil stays are twig like at the dropouts (Nervex Professional lugs and Campagnolo dropouts).

A poster on another forum has a late 40s frame that weighs exactly the same - there's an idea that it could Accles and Pollock Kromo.

[Brucey]

yes it could be AP Kromo DB; I have had a frame built in that tubeset and it too was similarly lightweight and (IIRC) took a 27.0mm seat pin.

cheers

[Des49]

Yes, I found that surprising too: 2325g v 1966g is a difference. I've ridden an Italian SLX frame and loved it but never tried SPX - unlikely for a 52/53cm frame size.

Your old frame is impressively light weight.

Just weighed some frames, not to the exact gramme as my scales are for heavier weights. These are all about 21" seat tube frames.
All painted, all except the SLX racing frame have had anti corrosion coating applied internally, so that may add a small weight gain. Fascinating to compare the weights to a modern racing frame which weigh a whole kg less!

SPX road racing frame 2.25kg fork 0.75kg
SLX road racing frame 1.90kg fork 0.70kg
SLX training frame 2.10kg fork 0.75kg

[avecReynolds531]

Yes, I found that surprising too: 2325g v 1966g is a difference. I've ridden an Italian SLX frame and loved it but never tried SPX - unlikely for a 52/53cm frame size.

Your old frame is impressively light weight.

Just weighed some frames, not to the exact gramme as my scales are for heavier weights. These are all about 21" seat tube frames.
All painted, all except the SLX racing frame have had anti corrosion coating applied internally, so that may add a small weight gain. Fascinating to compare the weights to a modern racing frame which weigh a whole kg less!

SPX road racing frame 2.25kg fork 0.75kg
SLX road racing frame 1.90kg fork 0.70kg
SLX training frame 2.10kg fork 0.75kg

Thanks, this is interesting - and to compare to the Columbus chart too. We grew up revering the white dove with red background decal on an Italian frame as something truly special in the world of road racing frames. The SLX frame (Somec) I mentioned earlier was probably the best riding frame I had the privilege of trying.

It seems surprising that frames from the 40s and 50s could be lighter.

yes it could be AP Kromo DB; I have had a frame built in that tubeset and it too was similarly lightweight and (IIRC) took a 27.0mm seat pin.

cheers

Thanks for this. I've no idea how the frame will ride - I'm guessing fairly flexible and comfortable? How was your frame?

I was surprised to learn that AP Kromo was air hardened - from Grace's guide: 'Many leading bike builders in the UK during the 1930s, '40s and '50s, preferred to use Accles and Pollock tubing as it was air hardening, unlike the manganese-based Reynolds product which was not. Air-hardening tube-sets actually become stronger when brazed, unlike the normal steel tubing sets, such as 531, which are weakened by heating. Air hardening products were not introduced by Reynolds until well into the late '90s, and are now being marketed to cyclists as the latest thing in steel. Accles and Pollock's Kromo tubing was used by Hobbs of Barbican, Rattrays of Glasgow "The Flying Scot" and Thanet in their "Silverlight" model.'

There's a fine endorsement advert of Kromo from Hobbs of Barbican here: https://web.archive.org/web/20050911200 ... dv_51.html

Historically, why did AP Kromo never achieve the same popularity as 531?

Thanks for further forum knowledge & advice.

[Brucey]

'air-hardening' all too easily becomes 'air embrittling' with some steels. Higher strength means higher residual stresses too (bad).

More modern CrMo steels can be microalloyed which helps to make the steel more tolerant to joining process variations.

If the cooling rate is low enough then CrMo steels won't embrittle when being welded. So for example I have seen plans for a CrMo helicopter spaceframe construction which uses gas welding rather than TIG, the reason being that it is virtually impossible to make a gas weld that cools too quickly (and consequently becomes embrittled), whereas it is quite easy with a TIG weld.

cheers

[scottg]

I've a 1954 frame, takes a Reynolds No. 4 post.
26.9 in new money. Start with a 27mm, emery paper to fit.