Frame Size - Quick Q

[Get Karter]

Advising my brother on getting a bike, I am stumped by the sloping top tubes of bikes and what that means for their sizing.

My brother, like me, is 6ft tall.
I have two old road bikes with horizontal top tubes, both 57cm (centre to top).

The bike he's looking at comes in a 56cm and a 59cm, but the top tube slopes down to the seat tube.

So my question is:
Is this 56/59cm the measurement to the actual top tube?
Or is it to a horizontal line from the top of the headset (i.e. as if the top tube were horizontal)so it fits with old school sizing?

Many thanks.

[itsnotarace]

Depends on the manufacturer as to how the sizing works but these days most frames are sized according to horizontal top tube length, or on sloping frames "virtual top tube" or "effective top tube" which is an imaginary horizontal line between the centre of the headtube and the centre of the seat tube.

[Get Karter]

itsnotarace said:

Depends on the manufacturer as to how the sizing works but these days most frames are sized according to horizontal top tube length, or on sloping frames "virtual top tube" or "effective top tube" which is an imaginary horizontal line between the centre of the headtube and the centre of the seat tube.

Makes sense. I'll tell him to get the 56cm and make sure the seat pin goes 1cm higher than mine.

Many thanks.

[khushy]

Sorry, but if you are stumped, let your LBS advise your brother.

Could be an expensive mistake, height has no bearing on frame size.

Khushy

Edited by khushy on Tuesday 20th December 07:49

[Crafty_]

Have a look on the manufacturer website, most will give you the distance between the stem and the seat post on a horizontal plane, e.g. marked as B' on the geometry diagram on this page : http://www.cube.eu/en/hard/comp/analog-disc-blackw...