Frame size measuring
06-16-25 | 09:18 AM
#1
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Frame size measuring
I just obtained a (free $$) road bike. It’s a TREK 1200 (not sure of the year). It has a sloping top tube. I want to be sure of the frame size, but not sure how to measure bikes with sloping TTs (most of my bikes are old with horizontal TTs). In looking for ways to measure, I’m seeing the phrase “effective top tube,” but not a complete explanation. Would that be a level (imaginary) line from the top of the head tube to the seat post? (Then measure from that point on the seat tube down to the center of the BB?) — Dan
06-16-25 | 09:31 AM
#2
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From: Québec, Canada
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What information exactly are you trying to obtain? Just in case, the frame size is no longer correlated with the length of the seat tube.
I would measure the top tube from the seat tube to the head tube where they connect (not from the centre of the head tube and seat tube) like shown here (2):
I would measure the top tube from the seat tube to the head tube where they connect (not from the centre of the head tube and seat tube) like shown here (2):
06-16-25 | 09:34 AM
#3
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I just obtained a (free $$) road bike. It’s a TREK 1200 (not sure of the year). It has a sloping top tube. I want to be sure of the frame size, but not sure how to measure bikes with sloping TTs (most of my bikes are old with horizontal TTs). In looking for ways to measure, I’m seeing the phrase “effective top tube,” but not a complete explanation. Would that be a level (imaginary) line from the top of the head tube to the seat post? (Then measure from that point on the seat tube down to the center of the BB?) — Dan
*maybe from the top of the top tube/center of the head tube? Not sure that it's make a huge difference to the actual numerical measurement
06-16-25 | 11:07 AM
#4
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That's exactly what it is- an imaginary horizontal line from the center* of the head tube/top tube junction to the center of the seatpost.
*maybe from the top of the top tube/center of the head tube? Not sure that it's make a huge difference to the actual numerical measurement
*maybe from the top of the top tube/center of the head tube? Not sure that it's make a huge difference to the actual numerical measurement
Dan
06-18-25 | 08:14 PM
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You can put a bike up against a wall and get stack and reach from two points and a measuring device + level, or with stem and bar installed 3 points. With stack and reach you can compare to anything.
scott s.
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scott s.
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06-19-25 | 07:42 AM
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[QUOTE=_ForceD_;23543601
In looking for ways to measure, I’m seeing the phrase “effective top tube,” but not a complete explanation. Would that be a level (imaginary) line from the top of the head tube to the seat post? (Then measure from that point on the seat tube down to the center of the BB?) — Dan[/QUOTE]
That's basically what I do. My sweet spot is a 54/55 frame with 55 TT. I put my bike on a level floor and measure as you describe. Works perfectly for me.
In looking for ways to measure, I’m seeing the phrase “effective top tube,” but not a complete explanation. Would that be a level (imaginary) line from the top of the head tube to the seat post? (Then measure from that point on the seat tube down to the center of the BB?) — Dan[/QUOTE]
That's basically what I do. My sweet spot is a 54/55 frame with 55 TT. I put my bike on a level floor and measure as you describe. Works perfectly for me.
