Many of us can fit more than one size frame of a given model. Conventional wisdom is generally to size down unless you want a particularly relaxed/upright fit. My question is whether this calculus changes for frames on the smallest end of the spectrum, where manufacturers often make geometry compromises that may adversely affect handling characteristics.
For context, I am 5'5" with an approximately 29.5" cycling inseam. For the last few years I have primarily ridden a 50cm Bianchi Infinito CV (circa 2014) and a 51cm Jamis Renegade (circa 2019). Both frames have an effective top tube around 525-530mm and relatively slack head tube angles of 71-71.5*. I have both fitted with 0 offset seatposts with saddles fairly forward. I'm running relatively short 160-165mm cranks on both rigs. I have sometimes wondered whether my need for 0 offset posts on these bikes indicates that they are slightly large for me, though I have ridden both comfortably for several thousand miles.
I'm interested in trying a new bike with racier geometry and handling. Looking at geometry tables, it seems that manufacturers differ in how well they preserve certain measures (e.g., trail) in the smallest sizes. Of course there are tradeoffs but it seems like a large part of the variation is whether the manufacturer uses multiple fork rakes across sizes. For example, Giant uses a single fork rake across TCR sizes resulting in trail ranging from 59-72mm from largest to smallest. On the other side, Cannondale uses 2 fork rakes and manages to preserve a narrow trail range of 58-60mm across sizes. This makes me wonder if certain brands are particularly well suited for shorter riders.
My LBS is a Specialized dealer and I'm quite interested in the Aethos. Given my measurements, Specialized recommends a 52cm frame. Yesterday I test rode both the 52 and 49cm. I think I could make either frame work, but for the 52cm I would certainly need a 0 offset seatpost and to push the saddle forward. I recognize this is likely not ideal in terms of weight distribution over the wheels. The pedaling position on the 49cm fit much better out of the box, and the complete build also comes with my preferred crank length and bar width. However, the 49cm has a significantly longer trail of 63mm compared to 58mm on the 52cm, which is more in line with larger sizes. Here is the geo table for reference:
https://www.specialized.com/us/en/ae...=299423-187066
My question is whether to follow conventional wisdom and go with the smaller 49cm frame that I can ride with the stock seatpost (12mm setback) or if the altered geo at this size will compromise the pin sharp handling I'm looking for, suggesting I should either size up or look at a different model/brand. How compromised do you think the handling characteristics will be on the 49cm given longer trail vs the 52cm?