threadless fork size: one size smaller for frame size

Quoted message said:

finally got a threadless all chrome Columbus fork for my Fondriest. But
the place where I got it from shipped me a fork for a 57 cm frame while
my frame is 58cm in size. The fork for the 58cm was too pitted for them
to sell it to me. Question: is there any problem in fork size wih
regards to frame size? Will a fork meant for a 57cm frame be ok to
install on a 58cm size? Just by eyeballing it, it looks a tad shorter
than my fork on there now. Just wanted to see if there was some sort of
standard rule for matching up a fork with a particular frame size or
can a fork measured for a specifc frame size be ok to mount on other
frame sizes that are within a cm or so. My headset is on backorder so I
wanted to nip this in the bud and ask here first and send it back if I
had to before taking everything apart and seeing if it would work or
not. Thanks.

As long as the crown-to-axle distance is the same, and the steerer
tube is long enough to permit the stem to be installed properly at a
useful height, there's no problem. If it flunks either test, I'd try
to cajole them into supplying the right fork instead.

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Quoted message said:

finally got a threadless all chrome Columbus fork for my Fondriest. But
the place where I got it from shipped me a fork for a 57 cm frame while
my frame is 58cm in size. The fork for the 58cm was too pitted for them
to sell it to me. Question: is there any problem in fork size wih
regards to frame size? Will a fork meant for a 57cm frame be ok to
install on a 58cm size? Just by eyeballing it, it looks a tad shorter
than my fork on there now. Just wanted to see if there was some sort of
standard rule for matching up a fork with a particular frame size or
can a fork measured for a specifc frame size be ok to mount on other
frame sizes that are within a cm or so. My headset is on backorder so I
wanted to nip this in the bud and ask here first and send it back if I
had to before taking everything apart and seeing if it would work or
not. Thanks.
-Mike

Forks, threaded or threadless, don't have any compatibility stuff
regarding frame size in terms of the frame's nominal size, which is
basically arbitrary and meaningless. Aftermarket threadless forks
generally come with a steerer that's long enough for any frame, and
they're cut down to size for the frame if desired. (Although with big
bikes that want lots of spacers, and with some really big bikes in
general, there can be issues with the steerer not being long enough).
How long the steerer needs to be is determined by headtube length,
headset stack height, stem clamp area height, and desired spacers. An
overhang of about 2-3 mm is left between the top of the steerer and the
top of the fork, where the topcap sits. Also, carbon and aluminum
steerers have limits to how much spacer should be between the headset
and stem (what those limits are if they're not specified is
contentious). Also, people who tinker sometimes don't ever bother
cutting their threadless forks, using a pile of spacers to fill the gap
between the stem and topcap. And in any case, cutting the steerer on a
new fork as soon as it's installed often doesn't make much sense
anyway, because it's an oppurtunity to mess with fit.

However, if you bought this from someone who says there's a difference
between their "57cm" and "58cm" forks, then you should measure stuff
and see if the steerer is going to be long enough for you. Numerous
sources can tell you how to do this. And if you're saying that these
are OEM forks specific to your frame, then maybe you indeed might as
well get the one that goes with your size frame, on the (very, very)
off chance that there's something different about them other than
steerer length between sizes, such as rake. Manufacturers don't really
do that, but I suppose it's possible.