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Double Butted Reynolds 531 Seat Tube Inside Diameter?

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Double Butted Reynolds 531 Seat Tube Inside Diameter?

Old 01-27-09, 07:20 PM
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Double Butted Reynolds 531 Seat Tube Inside Diameter?

Per what i have read most standard bicycle tube sets have a particular seat tube inside end diameter which varies by make and type of tubing.

Does anyone know what the inside diameter of the Reynolds 531 double butted seat tube is and what the correct diameter seat post should be? My recently bought Peugeot frame with French language Reynolds 531 sticker on it had 26.0mm seat post installed as bought. I suspect this may be incorrect.
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Old 01-27-09, 07:42 PM
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it would be 27.2 however there are allot of "but"
-there are many other (mostly high quality) tube sets that are 27.2 as well
-it may be straight guage and not double butted but still be 27.2 (might be wrong on this)
-the 531 in taller bikes was of a thicker guage

it would probably be easier to just identify your frame model and year, then lookup the corresponding spec's
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Old 01-27-09, 07:49 PM
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Originally Posted by SingeDebile
it would be 27.2 however there are allot of "but"
-there are many other (mostly high quality) tube sets that are 27.2 as well
-it may be straight guage and not double butted but still be 27.2 (might be wrong on this)
-the 531 in taller bikes was of a thicker guage

it would probably be easier to just identify your frame model and year, then lookup the corresponding spec's
None of that applies to a PX10 with metric-sized tubing.

My '74 PX10 takes a 26.4.
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Old 01-27-09, 07:50 PM
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I think it varied. I've had 26.8 to 27.2 fully butted Reynolds English bikes, and the French bikes were even smaller inner diameter...
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Old 01-27-09, 07:56 PM
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Originally Posted by Dirtdrop
None of that applies to a PX10 with metric-sized tubing.
hmmm interesting, so you mean the 531 for some french bikes ie: px10 had differing wall thicknesses from the 531 used by other manufactures. or am i getting this totally wrong

Last edited by SingeDebile; 01-27-09 at 08:04 PM.
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Old 01-27-09, 08:00 PM
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Originally Posted by SingeDebile
hmmm interesting, so you mean the 531 for some french bikes iex10 had differing wall thicknesses from the 531 used by other manufactures. or am i getting this totally wrong
French bikes used metric-sized tubing. The outside diameter of a Peugeot seat tube is 28mm instead of the normal 28.6mm (1 1/8"). That's why they take odd-sized seatposts and why some clamp-on front derailers tend to slip on French seat tubes.

Last edited by Grand Bois; 01-27-09 at 08:05 PM.
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Old 01-27-09, 08:05 PM
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The French used a different size Reynolds 531 tubeset than everyone else.

The British/I.S.O. standard seat tube outside diameter is 28.6mm, while the French standard seat tube outside diameter is 28.0mm.

Seat tubes are single butted, not double-butted; the butted end goes into the BB shell. The most common British/I.S.O. 531 seat tubes have 0.9mm walls on the BB shell end, and 0.6mm walls on the seat post end. 2 x 0.6mm = 1.2mm, which, when subtracted from 28.6mm, yields an inside diameter of 27.4mm. However, the tolerance on the wall thickness and roundness of the seat tube made it so that you rarely could fit a 27.4mm post inside, even before brazing. And then, the seat tube always got distorted during brazing, making it even less possible to fit a 27.4mm in there, but a 27.2mm fit nicely.

My guess (and this is only a guess!) is that the French 28mm O.D. seat tubes also have 0.6mm walls on the seat post end, so 2 x 0.6mm = 1.2mm, and 28mm minus 1.2mm = 26.8mm. Then subtract 0.2mm for the wall thickness and roundness tolerance, and distortion from brazing, and you'd get a seat post diameter of 26.6mm.

EDIT - I just read Dirtdrop's response that his PX10 takes a 26.4mm seat post. That passes my sanity check...
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Last edited by Scooper; 01-27-09 at 08:10 PM.
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Old 01-27-09, 08:06 PM
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I received an e-mail from Reynolds awhile back and it basicly stated the I.D. could vary from 26.6 to 27.2 depending on the tubes being Imperial or Metric, the set your starting with and a manufacturer boring out the tubes.

I asked, "what size seatpost does 531 tubing accept?"

Reynolds reply: (Peugeot switched to Imperial tubing around '81-ish)

this is really difficult to reply to.
>
>You see when we supplied Peugeot we did supply tubes that were metric size
>(28.0mm outside) and imperial (28.6mm outside).
>Then in each diameter the thickness of the tube was also supplied, 0.7mm or
>0.55mm.
>The frame builder would also ream the inside of the tube, so really it could
>be a 26.6, 27.0 or 27.2 depending on the seat tube and reaming done.

Last edited by miamijim; 01-27-09 at 08:10 PM.
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Old 01-27-09, 08:18 PM
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Originally Posted by miamijim
I received an e-mail from Reynolds awhile back and it basicly stated the I.D. could vary from 26.6 to 27.2 depending on the tubes being Imperial or Metric, the set your starting with and a manufacturer boring out the tubes.

I asked, "what size seatpost does 531 tubing accept?"

Reynolds reply: (Peugeot switched to Imperial tubing around '81-ish)
Thanks. Sounds like the prior owner overtightened the seat clamp as the seatpost installed was a 26.0 one. Apparently my frame is a 72 or 73 as the Reynolds sticker is in French. The head tube lugs look like the photo of the 74 PX-10 on miamijim's Peugeot web site rather than the fancy ones from the 70-73 catalog photo. The lugs are painted black however as in the 70-73 photo but I have no idea if this is original.
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Old 01-27-09, 08:21 PM
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FWIW, my 80s Reynolds 531 frame takes a 27.2 seat post. Same as my '07 Bianchi aluminum frame...
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Old 01-27-09, 08:23 PM
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My very dusty '74 PX10. Of all people, Miami Jim should know the correct size for a PX10.



Sheldon's seatpost database says that a '73 takes a 26.4 and a '76 takes a 26.6.

Last edited by Grand Bois; 01-27-09 at 08:36 PM.
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Old 01-27-09, 08:47 PM
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Originally Posted by Dirtdrop
My very dusty '74 PX10. Of all people Miami Jim should know the correct size for a PX10.



Excellent picture!!! Notice the slot gap is parrallel from top to bottom which is an indication of proper seat post size!!

26.4mm is too small for both of my '72's.
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Old 01-27-09, 09:09 PM
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Originally Posted by tatfiend
Thanks. Sounds like the prior owner overtightened the seat clamp as the seatpost installed was a 26.0 one.
It's worth getting right, since an undersize seat post can give you fits, working its way loose chronically. Since Reynolds apparently drew the metric-sized tubing to the same wall thickness used on Imperial-sized tubing, and the standard seatpost for a 70s/80s R 531 Imperial tube was 27.2, it stands to reason that 26.6 would be correct for a Frenchie (0.6 mm smaller OD). However, if it's a large frame, it might be possible that a double-butted or straight-gauge tube was used for the seat tube. I will give you a couple examples:

1. I have a Jeunet frame that is certainly R 531, since the fork blades still have Reynolds decal remnants, and the frame is fairly light, too, for a 63 cm height. But the seat tube measures 26.0 or 26.2. I haven't built it up, so I haven't had my trusted LBS check this out (I have only a dial caliper), so it may be, like you say, a larger seatpost that someone fit a too-small seatpost to along the way. But my bet is that because the frame is so large, the constructor used straight-gauge tubing.

2. I do have an English (Falcon) frame that came to me with a 25.4 mm seatpost. The seat tube was ovalized at the top, measuring 26.6 at the max (athwart) and 25.8 min (fore-aft). I re-rounded it to the best of my ability using a stem in conjunction with a brass shim, and patiently tightening/checking/tightening/checking. I got it pretty round (26.2- x 26.0+), then took it to the "professionals." They at first thought that it would take a 26.2; but using their reamer and trial posts, they determined that it actually took a 26.4! They showed me with a very long post that went right down the tube. I'm virtually certain that this bike is not DB tubed, because it's not light, and the tubing is seamed, not seamless. And if it were DB tubed, it's more than likely that the seat tube would be single-butted anyway.

OTOH, you might have a bike with a single-butted tube that's just got a bit thicker wall than Reynolds suggested to miamijim. Then too, a 26.4 mm PX-10/Simplex post just sold on eBay. Best course is trial and error, with the proper tools.

Last edited by Charles Wahl; 01-27-09 at 09:24 PM.
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Old 01-27-09, 09:28 PM
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That Simplex post on eBay is steel, for a sixties PX10. Otherwise I'd bid on it.
I'd much rather have a correct Simplex post than the high zoot single bolt Super Record post I have in there now.
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Old 01-27-09, 10:22 PM
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My Austrian Puch - 1982 - takes 27.2mm. So the Austrians were sane...
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Old 01-27-09, 10:35 PM
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Originally Posted by miamijim
I received an e-mail from Reynolds awhile back and it basicly stated the I.D. could vary from 26.6 to 27.2 depending on the tubes being Imperial or Metric, the set your starting with and a manufacturer boring out the tubes.

I asked, "what size seatpost does 531 tubing accept?"

Reynolds reply: (Peugeot switched to Imperial tubing around '81-ish)
What about HLE tubing? That seems to take a 26.0 post - and it's not because the tubing is gas-pipe.
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Old 01-28-09, 12:05 AM
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RE: Charles Wahl:
Since Reynolds apparently drew the metric-sized tubing to the same wall thickness used on Imperial-sized tubing, and the standard seatpost for a 70s/80s R 531 Imperial tube was 27.2, it stands to reason that 26.6 would be correct for a Frenchie (0.6 mm smaller OD).
my wife's reynolds 531 extra leger '81 andre bertin c70 uses a 26.6 seatpin
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Old 01-28-09, 12:31 AM
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My 1987 Trek 400 takes a 27. I bought a 27.2 for it but couldn't get it in past a inch or so. The 27.0 fit perfectly.

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Old 01-28-09, 03:19 AM
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Another data point: I picked up a frame recently that I believe is a 70s Allegro--Swiss made w/ French threading and sizing. It still has remnants of its Reynolds DB 531 sticker, and it takes a 26.6mm seatpost.

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Old 01-28-09, 04:15 AM
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Go to Sears and buy a dial micrometer for 20 bucks.
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Old 01-28-09, 05:41 AM
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I have a 74 Motobecane Grand Record that is DB 531. It came with the original Campy seatpost and is 26.4.

My 73 Raleigh Super Course is straight gauge 531 and also takes a 26.4 seatpost.
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Old 01-28-09, 07:05 AM
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From Reynolds:

In the 1970's there was only France, Spain and Switzerland that used metric tubes.
I suppose that could be interpreted to mean French, Spainish and Swiss bikes woud take a 26.4 or 26.6 while the rest would take 27.0's or 27.2's.
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Old 01-28-09, 09:07 AM
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Originally Posted by Scooper
The French used a different size Reynolds 531 tubeset than everyone else.
LOL - who woulda thunk it?
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Old 01-28-09, 01:16 PM
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Some very interesting bike history coming out here so I am glad that I asked the original question. I, obviously along with many others, was not aware of the Metric versus English 531 tubing size difference. Always something new to be learned.
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Old 01-28-09, 08:56 PM
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In the English sizes there were 3 weights of 531. SL, Standard, Heavyweight (Later called Tourist, I assume at the suggestion of a marketing type.)

The SL and the Standard both had nominal 27.46mm seat tube IDs. The butt was thinner on the SL. Some skilled builders such as Chris Kvale would occasionally have so little warping that they could use 27.4 seatpost.

Heavyweight/Tourist had a nominal 27.15mm seat tube ID. My Jack Taylor Lugged Tourist takes a 27.0 seat post.

BTW My 23" 1957 Raleigh Record Ace 531 frame weighs only 4 lb. 3oz. yet takes a 1" seat post. Raleigh brazed in an internal sleeve so dealers would only have to stock one seatpost size.
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