Just joined the forum. What a great resource - thanks everyone for all the helpful information.
I'm trying to make sense of LightCarbon's sizing recommendation for the LCR018-D. They recommend a 52cm for riders 173-179cm. That frame has an effective top tube of 535mm and a standover of 75.6cm.
For comparison, a 51cm Cannondale Synapse is recommended for riders 165-175cm It has an effective top tube of 542mm and standover of 75.2cm - not very far off from the LCR018.
A medium Trek Domane Gen 5 is recommended for riders 162-173cm. It's effective top tube is 541mm and much higher standover of 775mm.
I'm 171cm with a 76.8cm inseam. The Synapse in 51cm and the Domane in medium both fit me. The LCR018 52cm doesn't seem any bigger than these endurance frames, and might even be a little smaller. And yet it's recommended for riders 173cm. I'd also be running 700x32 tires, which might drop the standover a bit more. But LightBicycle recommends the 50cm for me, and from what I'm reading here, that would probably be what most people would recommend for me as well. But it really seems like a 52cm LCR018 is the closer match to these other frames that I know are my size. I need the higher stack of the 52cm. I'm moving from a silly-looking 52cm Aethos with a massive spacer tower and 17 degree stem. I'd still probably need 20-30mm of spacers on the LCR018. The 50cm would probably fit too, but everything points to the 52cm for a 171cm rider.
Am I missing something?