Ok so I'm getting a new frame soon and I'm trying to determine the appropriate stem length. I would get fitted at an LBS but they wanna charge an extra $15-20 for a stem (in this case a nitto pearl) that I could get online cheaper. I'm already gonna pay them to swap parts for me so don't give me sh*t about not supporting my LBS.

Anyway, the frame I plan on getting has a slightly diff/less aggresive geo then my current bike. I'm just trying figure out whether or not I would need to get a longer, shorter, or a stem with the same length.

All in mm

This is the geo of my current bike:
Seat tube: 530
Top tube length: 535
chainstay: 383
Head tube angle: 74
Seat tube angle: 75.5

Geo of the frame I plan on getting:
Seat tube: 517
height from bb to top tube: 490
Top tube length: 535
chainstay: 385
head tube angle: 72
Seat tube angle: 75

I currently run a 100 mm stem (stem is level) and I feel very comfortable with it. Obviously this new frame is not as aggresive and I'm not trying to replicate that. I'm just trying to figure out how much of a shorter or longer stem I would need considering the head tube angle. Or does that even matter considering the top tube length is the same. I'm not sure if this question makes sense so please feel free to re-phrase what i'm trying to ask here.

god damn you for not supporting your LBS

this may help:

https://www.brightspoke.com/t/bike-stem-calculator.html

Do I even need to get a stem that's a different length? I'm running threadless right now btw with some spacers that are pretty much the same length as the shaft of the nitto pearl.

with my experience, as long as the fit is in the ballpark, your body will become used to the set up. No matter what, once you hop on your new bike it will feel weird. But, I currently have a 110x10ºx31.8 stem I am trying to switch out for a 80 or 90mmx0º stem. In theory its a fair difference, but im sure after a couple rides ill be alright.

You can always add or subtract spacers, flip stem, adjust bars, adjust seat, etc.

If you agreed to pay them then they might give a sh*t about your bike turning out right.

But alas, you as BF who doesn't give a sh*t about your bike.

That stem calculator is designed for threadless stems. Not quill stems.

Punch all those specs into the free bike cad program and compare the two bikes that way.

https://www.bikeforest.com/CAD/bcad.php

I expect the difference to be nominal and your bars will come back a little but not enough to warrant a 110 mm stem if everything else remains the same.

Carleton, I'm ordering the frame and bringing it the LBS I always go to (for minor issues or part changes, I don't have all the necessary tools at home) to swap parts. So i do give them business all the time. However, I would like to save a little dough considering how much I'm gonna be dropping on the frame and some new parts. Also, I don't like to haggle or ask for favors and keep in mind my friend this is NY, nothing comes cheap here.

And I do give a sh*t about my bike, a little too much sometimes.

My LBS has too much snark.

Ignoring the differences in seat tube angle/length, assuming that both top tube lengths you've listed are the "effective" top tube length, and also assuming it's a 17º stem (which would obviously put it perfectly horizontal with a 73º headtube) there shouldn't being any change in reach going from 74º to 72º. Basically just going ± 1º around horizontal. Cosine is an even function, e.g. 100mm*cos(-pi/180 rad)==100mm*cos(pi/180rad)—so your reach should remain unchanged.* But to achieve this, you might have to adjust the height of the stem by 2*100mm*sin(pi/180)==3.5mm. In other words, just ride the damn bike and don't worry about these little differences.


*bit drunk & sleepy right now so 8th grade geometry skills might need to be double checked.

i was and still am horrible in math but yeah that seemed pretty explanatory chief. thanks.