how do you measure the size of a bike?

Question

Where on a bike frame do you measure to and from in order to ascertain the frame size?

Answer 1

Measuring Frame Size
Generally, when you see a single number listed as a frame's "size" that number refers to the length of the seat tube .
A further complication is that nobody knows how to measure a bicycle's seat tube any more. Even leaving the inches/centimeters question out of things, there is the question of where the seat tube ends:

The old standard system was to measure from the center of the bottom bracket to the very top of the seat tube.

Some manufacturers have decided that this is too easy, so now many bikes are measured instead to the intersection of the centerline of the top tube with the centerline of the seat tube.

Some other bikes that have seat tubes that protrude farther than normal above the top tube measure as if they were measuring to the to the top of a seat tube with normal protrusion.

Some bikes are measured to the top edge of the top tube, even though the seat tube protrudes higher up.

Some bikes with slanting top tubes are measured as if there were a level top tube, they use the length that the seat tube would be if it was as high as the head tube.

Anarchy reigns; I know of one bicycle line that made a running change in the middle of the year. You could have two bikes of the same make, model, year and nominal size, but one was 2 cm larger than the other! The only way to know was to measure them.
An additional complication is that the height of the bottom bracket varies over a considerable range, typically anywhere from 10.5" to 13"! Thus even frames that use the same system for figuring the top of the seat tube may have widely disparate stand-over heights.

Bottom line: seat tube "frame size" numbers are nearly meaningless unless you know how they are measured!

Answer 2

It depends on the manufacturer - Some measure from the center of the bottom bracket to the "Top" of the seat tube - others measure from the center of the bottom bracket to the center point where the toptube crosses the seat tube... And some even get more confusing by measuring to the top of the top tube..?

I find the more critical fit on a road bike to be cockpit length ~ so don't worry about too much/too little stand over, if the cockpit is too short or too long, you won't be comfortable.

Furthermore, in most cases, a frame can be more accurately described by measuring the top tube length - Center of Head Tube & Top tube to the center of the seat tube & top tube junction.

Mountain Bikes are different - They are measured by the seat tube length, there is little consideration for cockpit length, some like a Mountain bike to fit a size smaller, to be more flickable on the trail.



I hope this helps you out!

Answer 3

Frame size was traditionally measured from the center of the bottom bracket to the top of the seat tube.

Answer 4

from the top of the saddle, to the bottom of the lower pedal that's the person size , the bike from the top of the frame were the saddle goes to the centre of the drive crank

Answer 5

Frame size and or diameter of wheels