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Old 01-13-22, 12:51 PM
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tiger1964 
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Location: Maryland, USA
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Bikes: Drysdale/Gitane/Zeus/Masi/Falcon/Palo Alto

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Originally Posted by Drillium Dude View Post
If you aren't getting a consistent read with a micrometer, perhaps the opening has been ovalized?
Or perhaps "user error"? Now, it's not much out, a tenth or two from min to max. Follow up question - what is the difference, if any, between set tube diameter and seta post diameter. Zero? "Interference fit"?

Originally Posted by T-Mar View Post
I'm surpirsed to hear 27.0-27.2mm in a 1974 Zeus, as they were were typically manufactured with metric standard tubing during this period, at least on the road models. Regardless, during this period Reynolds offered their standard 531 single butted seat tube in two different gauges and the plain guage seat tube in three different gauges. In both cases, the heaviest gauge seat tube was intended for a 27.0mm post, so that could be the correct size. It was common to spec the heavier gauge tubes on larger frames. It would also be appropriate for track frames intended for sprinting, where stiffness is a desired characteristic. This may also be the reason for the larger diameter, imperial standard tubing.
I am leaning towards thinking I should be looking at 27.0, but again that's conjecture.

Originally Posted by Wildwood View Post
My early '70s Zeus with metric 531 has a seatpost of 26.6mm. It is not a track bike.
Hmm. Wild card. again, " what is the difference, if any, between set tube diameter and seta post diameter." If it's somewhere about .5mm clearance, that 26.6 starts to make sense.
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Larry:1958 Drysdale, 1961 Gitane Gran Sport, 1974 Zeus track, 1988 Masi Gran Corsa, 1974 Falcon, 1980 Palo Alto. Susan: 1976 Windsor Profesional.
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