Frame Sizes - Trad v Compact

Paul said:

I now have the opportunity to buy a compact framed bike which basically
cocks up the computer fit, as this is aimed at trad frames. From the
measurements below, both recommended and actual from the compact, how much
can I allow for in terms of the compact frame (i.e. how much smaller would
be acceptable without the bike being deemed too small?)

Top Tube

Recommended (Trad Frame) - 576mm

[snip]

Quoted message said:

For the record I am 5 feet 11 inches with a 31 inside leg.

Thoughts anyone?

You really need to sit on the thing. Although a "58cm compact frame"
will often mean "58cm if this were a trad frame" - i.e. they measure
a hypothetical horizontal top tube length.

--
jc

Remove the -not from email

I'm the same height, with slightly longer legs. I ride a 73 degree
parallel 56.5 cm top tube traditional frame. It so happens with this
geometry that the seat tube can be the same length. There are at least
two methods of measuring seat tube length (c-c, c-t). Your fitting
methods have shown that you fit the norm for this too.

Most compact frames now quote a "virtual" top tube length. This is the
horizontal distance from centre of steerer to centre of the seat pin.
The length of the down tube, which is the normal measure of frame size,
for a compact frame is irrelevant, it is virtual top tube length that
matters. Compact frames have longer real top tubes and shorter down
tubes to help standover. The most compact compact frame is of course
the women's mixte frame.

Length of exposed seatpost is irrelevant, I ride a Brompton!

Quoted message said:

From the details provided, if the virtual top tube is 540mm then the

frame is too small. If the actual top tube is 540mm, then the frame is
much too small.

regards,
daren
--
remove outer garment for reply