Properly sizing a frameset online (Ritchey Road Logic)?

1. I've found ordering frames measured based on stack and reach have yielded the best results vs. using a height chart. I'd also compare bb height and horizontal head tube length as that will also influence your body's position on the new frame vs. old.

2. Looking at other posts on the subject, sizing down seems to give the most flexibility but it may depend on what you have currently. For example, if your current bike has a 120mm stem you may be able to adjust to a 140 if you need more reach or a 100 if you need less. But, if you are already at 100 going down to 90 will start to limit how much more adjustment you can do. The same logic would apply for saddle position, is it maxed out in the fore or aft positions?

Based on your info it seems like the 55 is the right size but you should measure out the Ritchey's stand-over and make sure there is some room between your crotch and the top tube.

If your body measurements are accurate, you've got an unusually long torso and short legs for your height, so fitting is going to be a little tricky. 55 cm would be about right for your inseam, but your arms would hang way out in front. The "stack/reach ratio" will tell you how laid out your torso will be on a given bike, and for someone with your build, you'd probably want a low ratio. For reference, a typical endurance bike, which would suit your style of riding but probably not your physique, has a ratio of about 1.5:1. This Ritchey has about 1.43:1, but my guess is you could go lower.

I would not get a smaller bike because your reach would be even more cramped on that.

It's easy to raise/lower a seatpost, and doing so doesn't really change the bike's dynamics. It's harder to lengthen/shorten a stem (since you need to replace it), and that does change the dynamics. There's limited adjustability for raising/lowering a stem, especially if you cut the steerer tube to size.

You might try e-mailing or calling Ritchey to get their advice.

I happen to be the exact same size, so I'll answer. I have a custom built road bike with 55cm c-t height and 57cm top tube. I'm using a 120mm horizontal stem and classic drop bars that have more reach than so-called ergo shape at the drops. If I for some reason wanted to have a stem with rise and ergo bars, I'd need even longer and lower frame. The 55cm Ritchey is a bit shorter and has a bit taller head tube but isn't that far off.

So, if you absolutely have to buy Ritchey, 55cm is probably the correct one unless know that your current frame fits perfectly and you want to change as little as possible.