Frame
07-30-17 | 06:55 AM
#4
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Generally it is from the center of the bottom bracket to the middle of the top tube at the seat tube or top of the seat tube (Schwinns were measured that way). With new sloping top tube bikes that has that has turned to the to the place on the seat tube where a straight top tube would have gone. Roger
07-30-17 | 07:05 AM
#5
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From: Los Barriles, Baja Sur, Mexico
Bikes: Look 585, Kirk Terraplane, Serotta Ottrott, Spectrum Super Custom, Hampsten Carbon Leger Tournesol
If you're referring to the way a manufacturer states the size of their frame, there is no 'standard' of frame measurement.
07-31-17 | 02:22 AM
#6
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From: NW Oregon
Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike
best way to measure frame size these days is... from center of head tube near it's top, to a center point on the seat tube or seat post directly rearward from the head tube in a horizontal, level line.
07-31-17 | 07:59 AM
#7
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From: Retired to Penang Malaysia originally from UK
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You need to look this up on the web there are loads of very good information & videos, also you have not mentioned what type of frame you are referring to, as there are several variations depending on frame design & type.
07-31-17 | 08:15 AM
#8
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center of BB along Seat tube is commonly called Frame Size
Top tube can be divided up by a plumb line thru the BB, set back behind, reach, ahead of that line.
that gives some idea of seat tube angle ... top tube length is just a total , center to center..
then chain stay length.. this is not saying anything about the fork
that's a separate set of answers.
...
Top tube can be divided up by a plumb line thru the BB, set back behind, reach, ahead of that line.
that gives some idea of seat tube angle ... top tube length is just a total , center to center..
then chain stay length.. this is not saying anything about the fork
that's a separate set of answers.
...
07-31-17 | 08:31 AM
#9
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Joined: May 2011
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From: Upstate NY
Bikes: Bianchi San Mateo and a few others
There is no single, uniform standard.
Traditionally, on road bikes with horizontal top tubes, frame size was measured along the seat tube. Everyone pretty much agreed that the low point was the center of the bottom bracket shell, but the top end of the measurement could be the center of the top tube, the top of the top tube, or the top of the seat tube. And because of geometry differences between makes and models, two bikes that are listed as the same size might fit differently. Their top tubes could be different lengths, for example.
On more modern road bikes with sloping or curved top tubes, numeric sizes generally aren't measurements, but equivalents to bikes with horizontal top tubes as rhenning mentioned above. My 2006 Bianchi has a sloping top tube, so we can use it as an example. It's a 53 cm frame, but its seat tube is only 50 cm long. If I was to draw an imaginary horizontal line from the junction of the top tube and the head tube back to the seatpost, that line would probably be about 53 cm from the center of the bottom bracket.
Some manufacturers don't even bother with 'virtual' or 'effective' measurements and just label them small/medium/large, etc.
...and if we're talking about bikes other than road bikes, different sizing conventions may apply. For example, road bike frame sizes haven't been listed in inches for a few decades now, but it's still the norm for mountain bikes.
Traditionally, on road bikes with horizontal top tubes, frame size was measured along the seat tube. Everyone pretty much agreed that the low point was the center of the bottom bracket shell, but the top end of the measurement could be the center of the top tube, the top of the top tube, or the top of the seat tube. And because of geometry differences between makes and models, two bikes that are listed as the same size might fit differently. Their top tubes could be different lengths, for example.
On more modern road bikes with sloping or curved top tubes, numeric sizes generally aren't measurements, but equivalents to bikes with horizontal top tubes as rhenning mentioned above. My 2006 Bianchi has a sloping top tube, so we can use it as an example. It's a 53 cm frame, but its seat tube is only 50 cm long. If I was to draw an imaginary horizontal line from the junction of the top tube and the head tube back to the seatpost, that line would probably be about 53 cm from the center of the bottom bracket.
Some manufacturers don't even bother with 'virtual' or 'effective' measurements and just label them small/medium/large, etc.
...and if we're talking about bikes other than road bikes, different sizing conventions may apply. For example, road bike frame sizes haven't been listed in inches for a few decades now, but it's still the norm for mountain bikes.
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