Comparing Stack/Reach - Existing Bike to New Bike
 

I’ve read that these numbers are pretty important when checking specs on potential new bikes. I know the stack and reach on my existing bike, and on three bikes I’m looking at. This new bike will be ridden like my existing bike though with wider tires. I can’t easily try these bikes at the moment (one is a buildup of a frame).

The numbers are below, existing bike bold font.

When I compare these, what are the things I should be paying attention to? Thanks 😊

Reach 383 / 392 / 394 / 378
Stack 575 / 566 / 557 / 565

Well if you want your fit to be just like your previous bike, then those as well as the rest of the geometry numbers should be about the same.

However if you want different fits on the different bike then you need to decide if you want a lower stack for a lower more aero position or do you want more stack for a more upright position. Reach can do somewhat the same for you with regard to making you more or less aero in position, but the two numbers really need to work together to match your particular desires, wants and needs. Since your body measurements and perceptions about your fit aren't mine, you really need to go see what they feel like.

I use the reach and stack to give me clues to what bikes I want, but not to just blindly pick a bike or size of bike.

If your bold numbers were my numbers, then I'd find all of the other number-combos comfortable. I have a number of bikes and have measured the stack/reach on all of them. For me at least, the S-R numbers of a comfortable bike is a general target as anywhere reasonably close (as your numbers are) would work for me. As Iride01 said..depends on what your goals are for n+1.

Based on these numbers, frames 2 and 3 both will have your handlebars being lower and further away than your current frame. Frame 4 will have a slightly shorter reach but lower handlebars. This is all assuming the same stem and steerer tube length. You can play around with different stems and possibly with different steer tube lengths (If your using a new fork) to get the bars into the same position as your current bike.

It would help to know whether you're looking for a fit that feels similar your current bike, or something different. As has been pointed out, your four choices are all lower than your current bike, and three of them are longer.

A low stack height can be adjusted with spacers under the stem, and a different stem length and/or angle can accommodate for reach differences, but only to a degree. Don't be this guy:

https://cimg1.ibsrv.net/gimg/bikefor...e30f2c6843.jpg

yeah that’s what I’m dealing with, as my existing bike is custom geometry and was based on a tall, short reach profile. I won’t replicate with off the shelf, but I’ve owned other bikes over the years and made them work.

Well consider the pic an example of a bike that has too little frame stack height for the position the owner wants to be in.

Please don't make a bike look like in the pic and ride them in public places! :p

The numbers you posted earlier are kind of moving in the opposite direction. Not sure what kind of a bike you're looking for (or your budget), but maybe folks here can point you towards a taller stack/shorter reach frame, if that's what works best for you. They're out there!

https://cimg0.ibsrv.net/gimg/bikefor...07d5557855.png
https://cimg1.ibsrv.net/gimg/bikefor...c9d51a6048.png

You obviously need to know stem length. Top tube length will also play a factor. Also important to consider saddle setback, hence which is why it is important to be able to try the bikes in person and make adjustments to saddle height, tilt, angle, setback, handlebar angle/position etc. as needed before comparing.

generally speaking, you can compensate for less or more frame reach by changing stem length accordingly, that is assuming that frame stack is roughly the same.

You can always manipulate the "effective" frame stack/reach with different stem lengths.

Don't forgot handlebar rise , reach, drop degrees whatever depending on flat/drop bar.

once frame stack starts to change dramatically, this is when comparos become slightly more difficult. some bikes have a long headset cup which changes the lower stack you can use. Others have cut steerer tubes. others dont. this is why stem length/degree combos are useful to achieve the effective handlebar stack/reach position you want.

Your stack/reach comparo is a good start. but dont be too critical, because like i mentioned there are other factors which may change your preferred fit. different frame geometries can work similarly well for you when comparing from bike to bike.

I'll say it like this, most of the statements you've made are correct. But, the presentation is haphazard and incoherent. You are clearly gaining lots of info, but info is not knowledge. This is not really helpful to the OP.

I ended up getting the bike that was the smaller frame, but exact same gravel bike frame as I had a few years ago and it fit well (Bombtrack Hook by the way). Spent a couple hours at the bike shop dialing in saddle height, fore/aft, and stem length and stack. Felt pretty good so we’ll see how she goes! Thanks for responses.