How do you measure a bike frame...

turbotommy

I have always been under the impression that the measurements on bike frames related to seat tube length. Eg a 61 speacialized tarmac would have a 61cm seat tube from centre of the bb to the top of the tube.... but is this the correct measurement? Seems like it bears closer resemblance to the top tube length.

To be honest I’ve not really paid this measurement much atfention since beyond a certain point I’m looking at stack and reach a lot more closely. Especially with sloping frames. But just recently I took a closer look at geo charts and I’m feeling like I’m going a little mad... hmmm maybe I need some sleep...

shirley_basso

Usually means 'effective top tube' - i.e when horizontal and is usually 2-4cm (or so) longer than the sloping measurement. Cube for some reason measure the other way and a 58 by their measurement is a 56 by most other bikes.

This website is great for a lot of bikes:

https://geometrygeeks.bike/

matt_n-2

Different companies do it differently.

A 58cm Specialized Tarmac for example means 58cm effective top tube length centre to centre.

A 58cm Colnago Master means a 58cm centre of BB to seat collar top with a 56.5cm top tube.

Same with a Colnago 54 sloping, 56.5cm effective top tube length.

Only way to tell is to check the geometry charts and compare between bikes.

neeb

In any case, it doesn't matter much as even if you knew that the number represented top tube or seat tube length you wouldn't want to base fit on that alone. Seat tube angle can add or substract a cm or two to reach for the same tt length.

Wouldn't it be good if frame sizes were just numbered in stack and/or reach?

kajjal

To compare bikes reach and stack are very useful measurements.

The main trick is to get a bike about the right size, not too big that you can adjust to fit.

jakejhonson44

Measure(in inches and centimeters) the two points(C & T)to identify the length of seat tube, for that will be the height of the seat tube.