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

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):

https://www.santafixie.co.uk/bloguk/...state-bike.jpg

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

Thanks. Also…this bike has the picture headset. Is this an adjustable stem in that the height of the stem/bar flats can be adjusted? Does that bolt need to be complete removed, and disassemble to make adjustment? It doesn’t seem to want to move when I loosen it.

https://cimg9.ibsrv.net/gimg/bikefor...2ab16611c.jpeg


Dan

Yes it is. Probably just a bit clagged up

Also don’t most Treks have the frame size printed on their seat tubes?

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.
.

Won’t tell you what frame size it is though?
(but maybe that’s not actually what the OP wants)

[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.