I’m looking to get a new bike soon and plan to get an updated bike fit.
I have 2 questions:
Get geometry charts for the bikes you’re interested in and compare to your bike fit.
I think this is probably a personal choice. I’ve seen many brand new bikes for sale on facebook. If you are mainly worried about which size bike to buy, then there may be some tools online either from your manufacturer or not that could tell you where you fit in the range. Canyon had a tool and it told me I was right in the center of the Large bike range. Given that, I was comfortable in buying a large. If you are on the edges, there may be more risk and it depends on what you plan to do with the bike. If comfort is your priority, then you may want to err on the larger size. If racing and weight are a priority, maybe the smaller size.
If you are trying to decide whether the geometry of different brands are right for you, that’s a tougher question. Fit for you is important, but I think most bike riders’ “feel” for a bike is really immature. Most of us couldn’t really notice minor differences in geometry between two comparable bikes, that couldn’t be addressed with a bike fit. Two bikes may initially feel different, but after a ride or two you probably couldn’t remember the differences unless you really hated it. I’m sure other’s have different experiences.
IF (and I mean a very strong IF) you are happy with your exact fit on your current bike, you can use a geometry comparison tool to check key measurements to predict fit on other bikes.
Key dimensions for fit are the Reach, Stack, Effective Top Tube Length (Related to Seat Tube Angle and Seat Post Setback for potential limits to saddle fore-aft positioning).
Key dimensions for handling are Wheelbase, Head Tube Angle, Fork Offset, Trail, Chainstay Length.
This depends on your experience and understanding of your current bike, in light of the potential differences in other bikes.
Reading reviews is good, but one person’s experience will heavily impact what they think is good or right. Look at a wide range of reviews and discuss with your local bike shop. Unless you have a real good understanding of the geometry and what it typical leads to for on the bike feel, you need to leverage those resources if you plan to buy without riding.
Edit to add: Getting the “Right Sized Bike” is super important. Fit can be adjusted with things like saddle height, fore-aft as well as bar position via Stem, Handle Bars, position on the Fork Steer Tube. But there are limits to what is possible without getting into undesired rider placement and/or weight distribution.
Point being, make sure to get the right starting point and then fine tune that via the bike fit process.
There are two different issues at play here: fit, and feel. Fit results from geometry: seat and bar positions relative to the bottom bracket axis (assuming fixed crank arm length). If you can bring the relative positions of these three parts to be equal between two bikes, you will get the same fit. Feel also results from geometry - but not directly connected to the rider: front wheel trail, BB height over the ground, chainstay length, stem length, etc, which all affect handling. Feel also results from stiffness (or lack thereof) in the various elements of the bike - wheels, rear triangle, BB, fork, laterally and longitudinally. There’s a link between these two - if you need a really long stem to get your bars in the right position, that will change the handling.
You select feel by selecting a bike model; you select fit by selecting a size. The first one is highly subjective, the second highly objective. Having bought used bikes a few times, I would pick the models I was interested in, look up the geometry of each, pick the correct size in each model (with reach and stack being the dominant numbers to look at), and go searching.