I'm looking at an image where it says your shoulder angle should be around 90 degrees and the angle of your back should be about 45 degrees for a road bike. I took some photos and am looking at some of my angles. I'm gonna do some better images in the future but for now I estimate my shoulder angle is about 86 degrees and back 50 degrees. So is there a reference to what changes I would want to make if I wanted to get closer to the 90/45 degrees? For instance if I raised my seat up a bit which I think I need to do anyway. That should also move it back a little which in my head is telling me it would decrease the angle of my back and increase shoulder angle. But I could be thinking wrong on that so just curious if there is a guide for these changes. Searching hasn't found me one so far. I'm really curious how angles are affected by moving the bars. For instance what would happen if I flipped my stem so the angle went down instead of up?

BikingViking793 : I'm all in favor of doing as much on your own as possible. However, when it comes to bike fit there's a lot that can go wrong if you don't have the proper skills, knowledge and experience. I highly recommend seeking out an independent, professional bike fitter.

That's great advice, but I'm trying to learn more about fitting.

What are you trying to accomplish? If it is to go fast comfortably, the goal is to find the best compromise between aero, power and comfort. More back angle is faster wind-wise. After a point, it starts cutting down on both comfort and power. Your fitness and flexibility are huge here. (All this said - seat position rules! And is so individual I am not going to even start to tell you what to do.)

I don't think there are magic numbers. I am skinny, long and light. I need a near flat back to go either fast or upwind. 45 degrees is me on the tops for a long hill climb or just cruising. (I ride stems where if I actually sit up, my hands are 10' from the handlebars.) I have also found that, for me, the magic "number" is actually a location - where my shoulders are relative to the seat and bottom bracket. That deternines an arc the handlebars to be on. Now I can have those bars fairly close and low or higher and further forward and get the same back lean, shoulder location comfort, power and ease of breathing. (Again, for me, that arc is basically a straight line for the short distance I am ever going to want the handlebars on. Any closer, my knees hit. Further and my long stems go to the absurd. That line, again for me, has a "slope" of 1 cm along the steerer axis and 2 cm along the horizontal. In other words, if a 12 cm quill stem pushed low works for me, a 14 cm quill a cm higher is just as fast and comfortable. Now only one mix of stem height and length is going to give me that magic 90 degrees. I never measure or even think to note that when I look in store front windows to check back lean. I have been all over the place relative to any set arm/torso angle on bikes the fit perfectly over the past 40 years. Arms further forward and higher? They are slightly more aero. Lower and closer. Better max power for steep climbs and hard accelerations though not as good for all day out of the saddle climbs.

I learned more about bike fitting in one session with my current fitter than I ever did previously. A good, independent fitter will teach you a lot if you ask questions and pay attention during the session. It is because of my bike fitter that I can now make bike adjustments on my own with the confidence that I'm making the correct adjustments.

You adjust saddle height to get correct knee angle and fore-and-aft to get correct balance, After establishing that, you adjust bar reach and height. Use a mirror if you can, have someone take photos if you can't. Move your hands around and look at your angles. As fat as bar height goes, with hands on hoods and forearms horizontal you don't want your thighs hitting your stomach or lower ribs when pedaling You want some gap there, doesn't have to be much. Depending on your leg length and build, you may never even get close to touching your legs to torso. If that's the case, it'd be nice if you were low enough to make your back horizontal. Above these limits will be less aero and air drag is always present unless you're on a trainer. These limits may also produce the "correct" hip angle in your normal hoods position, so looking at this is a good thing to try. If you think you have a close guess about stem length and angle, stems are quite inexpensive online. Over the years, I've changed stem length and angle a few times and so have a few "spare" stems. I have a bike fit primer here: How can I fitting my bike

There's a website which shows the effect of changing stem length and angle here: Stem Comparison Tool | yojimg.net
If it won't come up for you, google it.

And there's also a bike fitting app for your phone: https://www.dcrainmaker.com/2013/10/...nt-review.html
This app might be just what you're looking for.

Sez who?

This aging rider, born when Truman was still President, started the 2020 season with a back that was somewhat more vertical than 45 degrees. And finished the season with a tabletop flat back. I’d have said that was not even possible for someone past retirement. But it happened. On the #1 bike there were no adjustments whatever through the season. All changes accomplished by riding the bike.

Go ride your bike. Listen to your bike. Your bike will tell you what to do.

Oh. Bike #1 is a Bernard Carré. Could not possibly be more French than that. To make it into what Americans are pleased to call French Fit would require non-French parts and major butchery. Not happening.