A little embarrassed with this question in 2025 but when I started cycling and yes even after several years of both road cycling and Triathlons, reach and stack were an unknown concept so I still follow KOPS and what feels right in terms of comfort, etc.
I hope to buy a Trek Domane SL 5 Gen 4 on sale before the New Year as several bike shops here usually have special offers in late November or early December. If I look at reach and stack on Treks`s webpage on size 54cm previously used on an Emonda some years ago it says reach 37.4 and stack 57.5 and excuse me but how do I proceed with that knowledge and my own body measurements? If someone can introduce me to the process for finding the right reach and stack that would be great.
Thanks & Regards
hsea17

Stack helps you weed out the bikes that might have too high or low a handle bar height. And reach helps you weed out the bikes that can put the bars too far or too close to you. You have to know what position you want to make it relative to you. And other things about the geometry can make reach and stack not give you the same bar position as a different bike with the same reach and stack, but other things different about it. Some like to use the horizontal top tube length to assess reach.

If you don't know what position you want or have experience with a previous bike and work from that geometry relative to what you want for your body position. Then you my as well just try them all out and see what you like. Actual test rides for 10 or more miles tell you more reliably than a ride around a parking lot.

You can plug all your measurements into a calculator or tool and come up with a bunch of other numbers the bike must match. But with out a extensive database of the geometries of every different bike you could buy, I doubt you'll make much use of it for real.

You've been around here awhile. What bikes have you had that you liked the way they fit you? And why. Or are you wanting to try a different position.

Some people only like a very upright position. Some like a very aero position. Some are okay in any position. And a large number never seem okay in any position.

The manufacturer's have a sizing guide for each model of bike they make. You should consider what it says. Though your preferences or other things about you might have you better served with a size or two larger or smaller. But again, you won't know if you don't try out the bike.

You don't have to use stack and reach. You can look at seat tube angle and effective top tube to compare your old geometry to the new bike. S&R are just another sort of data point for those who already have a number in mind.

Maybe it's just menopause, with a head that thinks like a 25-year-old (at least when it comes to endurance sports and cycling) and my ego that doesn't quite accept that my body doesn't have the same flexibility as before and doesn't want to follow my thoughts anymore. When I think back, a 54 cm Trek Madone 5.2 is probably the one that has suited me best, but at the time I was competitive, so that's another chapter. But something that is probably common as you get older is that I have shrunk a couple of cm, but then again the inseam is about the same as before! Anyway, it at least makes me try some small adjustments even though I won't get faster anyway but at least I have something to pass the time with when I'm not out pedaling.
hsea17

What's also common as we get older is that typically do less and less activity. So muscles don't get worked as much. And they don't support joints and skeleton as well as they use to. So that bike that use to be comfortable starts to cause discomfort and pains. So make sure to actively get your muscles a good workout.

The only muscle that gets a good workout on a bicycle is the heart muscle. Leg muscles are about the only other thing that get a workout. But not through their full range of motion which will eventually be a issue.

I've recently learned (the hard way) that you have to be fit, through strength training and so on, before undertaking a particular sport or activity.
You do your preferred activity from a base of genaral fitness. Cycling by itself is nowhere near enough.
It takes hours per week of general fitness training to achieve and maintain a healthy body, to slow down aging and even rejuvenate if you're currently way out of shape like I was.
There are some big categories of fitness that all have to be addressed like strength, mobility, flexibilty, stability, cardio/endurance, core, balance, posture, body weight, etc.
It's really worth investing a lot of time in one's fitness. Not only will you probably live longer and healthier, but it just feels great to be in shape.

Reach and Stack, help in determining some general start point for a rider position and posture on any type of bike (mtb, road, TT, gravel, etc) relative to what they're looking for and their body structure.
Reach and Stack, for a rider who already has/had multiple bikes will likely be compared and adjusted relative to how they ride their other/prior bikes...
There are no absolutes, even are no real 'median zones' for Reach and Stack - it's what you wish...
In your bike list you have a number of performance road bikes, including an AL Domane.
So I would advise considering what differences you wish in your position and posture and relate that to the existing/prior bikes and then consider what you want from the new Domane.
Higher bar height? Less Reach to the bars? The frame is only the foundation to that - so many other things affect that, like Stem and Bar...
Or are you just wanting a New Bike ? Or the new 'stuff' on the bike? How much is about the bike and how much about the riding?
Often 'comfort' things are grounded, not in the bike, but in your posture - which unless you address that directly, a new bike may not make a difference.
Ride On
Yuri

Hmm, where did that post go? I posted here yesterday, but...
Anyway, it was mostly to say "thanks for the replies", and I mentioned that I still work out a couple of hours a week, but have bad knees, so I'm likely way too careful with leg strength training, which again isn't that great for maintaining strength in the thighs and hamstrings. I also updated some body measurements a couple of days ago and put them into an online bike fit calculator and got some surprising results in terms of effective top tube length and seat tube. But again, I don't think I shall put too much weight on that as it seems to me as almost every bike fit calculator has a different way of describing how to take body measurements.
hsea17