Anyone want to take a crack at the defining optimal fit? Describe how one knows when their bike is really dialed in for their body size and riding style. Lp

If you can ride it 100 miles without body discomfort. I am not talking about being tired but instead saddle pain or knee pain or hot foot etc. Roger

Some rough first approximations:

Seat-to-pedal distance: You should get a decent, but not full/locked, knee extension.

Seat-to-handlebar distance: With your elbow against the nose of the saddle, do your fingertips just touch the horizontal center portion of the bar?

Relative heights of seat and handlebar: My bars are about 4-5 cm below my saddle, but many folks favor equal height. This one is highly personal.

As rhenning asked, are you discomfort-free after a long ride? I would add, "Do you feel secure and stable on the bike?"

hmmm, now this is going to be interesting, and difficult.

I suggest you read these as a start.

https://www.peterwhitecycles.com/fitting.htm
https://sheldonbrown.com/frame-sizing.html
https://sheldonbrown.com/kops.html

There's also a good artlcle on Stem height in the current
Road Bike Action, with at least one 'vintage' viewpoint.

Marty

For a typical 70's early 80's race bike, the seat post should be out of the frame about 4", the 100-120mm stem should be out no more than 2", the ends of the handlebars should be parallel to the top-tube, the brake levers should be centered on the hooks, the saddle should be level with the top-tube or pointed up slightly. Now the bike looks right so it must be comfortable. Oh and keep the brake cable housings nice and short, as long loopy ones spoil the look, which can be very uncomfortable.

Ill leave the numbers and formulas to others. From a more prosaic view, I think "optimal fit" means:

For a serious pro/Cat I amateur racer - you are dialed in if (a) you can go faster longer and (b) you aren't so beat up afterwards that you can't do it again tomorrow, even though you are still sore as hell.

For everyone else - you are dialed in if the bike feels like it disappears under you on a long ride (whatever you consider a "long" ride). A dialed-in bike makes it feel like the only limitation is your cardiovascular condition, not any body-part pain or any mechanical issue.

Comfort.
If you can ride for hours without being sore.
I have been told I ride frames to large for me. I can stand over them and have from no clearance to over an inch.
But I have long legs and arms, and I am all cramped up on smaller frames. So I buy what feels comfortable for me.
I have read it all and tried the ideal fit, which sometimes is far from ideal, but you need to find what works for you.

never heard this one before so i tried it on 2 of my working bikes. the first is a bike that i've just finished building and have been stressing about the "fit" even though i've been fit before and we set it up with "correct numbers", the other is a bike that i just picked up off of CL and know that it's too long (reach-wise) for me.

guess what? i did the elbow trick and my tips just touched on the bike that was set up properly, and the CL bike that was too long, was indeed too long by a few cm's.