i want to upgrade the frame set on my bike but the frame i want is either a little shorter or a little longer than what i have now. given the impossible nature of recommending frame sizes over the internet, i'll still ask your opinion and not hold you responsible if its the totally wrong size (maybe).

Current is:
TT - 560mm
STA - 73
HTA - 73
it doesnt give measurement for the head tube, but taking a ruler to it, it measures 115mm which seems really short compared to most other bikes i see. i measured in between the headset cups and dont know if thats the right way to do it. if i include the headset cups its 130mm.

the bike i want comes in either
Medium
ETT - 547
STA - 73.5
HTA - 72.5
Head tube length - 145

L
ETT - 570
STA - 73
HTA - 73
headtube length - 165

didnt include the seat tube length because it doesn't really matter and one frame is ridiculously compact anyway.

I feel comfortable on my current frame, with a setback seat post and the saddle pretty much centered on it with a 100mm stem. KOTS is spot on, i can't see the front hub from the hoods, and most importantly, i can ride it for 4 hours with out problem.

i included a video riding my current bike. my elbows were pretty close to locked in it, but i have no clue why since i normally ride with very relaxed arms. i'll call it stage fright...



HAAALPPP

Ignoring angles, your total reach is 56cm + 100mm = 66cm. You could either go with the larger frame and use a 90mm stem or go with the smaller frame and use a 110mm stem (0.3cm off, but close enough). I'd say the smaller frame gives you more room for error.

thats what i was thinking as well, but the radically longer head tubes on both has me worried, would i end up very upright with large? they're planet X carbon pro sl frames, in case it matters.

How many spacers are you running and how aggressive is the angle of your stem? It's hard for me to tell from the video.

heres a quick pic of it



it has about 12mm of spacers and its a 100mm long, 6 degree stem. it has 12 cm of handle bar drop. i would to run no spacers and either a flat stem or slightly pointed down. while keeping the same amount of drop.

I don't think you'll have a problem recreating the handlebar position. It just becomes a matter of mathematics. If you had no spacers and your stem was angled down I'd be more worried about it. Maybe some of the more mathematically-enabled members of the forum could give you some exact calculations.

You can also try playing around with this: https://www.bikeforest.com/CAD/bcad.php

No brainer - get the smaller frame. The steeper STA adds about 5mm to the reach.
Your flipped up 100mm stem is only about 90mm in horizontal length. With the new
frame, you can flip the stem down and probably use a 110mm.