Seat Post diameter question.
10-28-07, 12:08 PM
#1
SkipM
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Seat Post diameter question.
Could someone explain for me why the measured diameter of a seat post is different from what is stamped on the seat post itself. For example, I have a Patent Campagnolo seat post (from a 1973 Italvega) stamped 27 but it measures 26.9 mm. Also I have a Pirmalux (Made in England) seat post (from a 1973 Holdsworth) stamped 26.4 mm but measures 25.8 mm. Thanks.
Skip Magnuson
Spokane, WA
Skip Magnuson
Spokane, WA
10-28-07, 01:48 PM
#2
Bottecchia fan
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I'd have to say the first one is just manufacturing tolorance but the second sounds like it's mis-labeled or severely worn. 0.6mm is a significant variation. Is it worn at all? Have you measured it in different locations to see if there is any variation?
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1959 Bottecchia Milano-Sanremo(frame), 1966 Bottecchia Professional (frame), 1971 Bottecchia Professional (frame),
1973 Bottecchia Gran Turismo, 1974 Bottecchia Special, 1977 Bottecchia Special (frame),
1974 Peugeot UO-8, 1988 Panasonic PT-3500, 2002 Bianchi Veloce, 2004 Bianchi Pista
1959 Bottecchia Milano-Sanremo(frame), 1966 Bottecchia Professional (frame), 1971 Bottecchia Professional (frame),
1973 Bottecchia Gran Turismo, 1974 Bottecchia Special, 1977 Bottecchia Special (frame),
1974 Peugeot UO-8, 1988 Panasonic PT-3500, 2002 Bianchi Veloce, 2004 Bianchi Pista
10-28-07, 04:59 PM
#3
My bikes became Vintage
How good is your caliper? Are you using it correctly? I just measured a Campag 26.8 seat post and it's pretty close.
10-28-07, 06:48 PM
#4
juneeaa memba!
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Polish. If a post is polished several times it will be considerably smaller (using a micrometer) than it was when new. 26.4 down to 25.8, though, thassa bunch. I have had a machinist friend turn down posts sometimes in the past to fit strange applications (shock posts in tandems, before that got trendy...)
10-29-07, 07:40 AM
#5
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I concur with thee above posters. The first case is almost certainly a combination of manufacturing tolerance, measurement accuracy and/or wear from insertion andd removal.
Case 2 is too extreme. In addition to the other suggestions, did you clean off the jaws of your calipers or micrometer before you measured it? It is quite possible that you picked up some grease and a small foreign particle from a previous measurement, especially if it was another seat post. Any foreign substance on the jaws would reduce the true measurement. It is good practice to clean the jaws prior to each measurement.
Case 2 is too extreme. In addition to the other suggestions, did you clean off the jaws of your calipers or micrometer before you measured it? It is quite possible that you picked up some grease and a small foreign particle from a previous measurement, especially if it was another seat post. Any foreign substance on the jaws would reduce the true measurement. It is good practice to clean the jaws prior to each measurement.
10-29-07, 10:56 AM
#6
My bikes became Vintage
If your measurement is less than what is stamped on the seat post, the problem could be one or more of the following:
1. You are clamping the caliper too hard.
2. Somebody has sanded or machined down the seat post (more like the former, because machining would also remove the stamping.
Seat posts often get ugly zig-zag scratches on them from trying to remove them and someone may have cleaned them up.
1. You are clamping the caliper too hard.
2. Somebody has sanded or machined down the seat post (more like the former, because machining would also remove the stamping.
Seat posts often get ugly zig-zag scratches on them from trying to remove them and someone may have cleaned them up.
