Originally Posted by
dalava
So if Paduano only does custom sizing frame, why is S&R even important unless you already have a frame with known S&R numbers and you want to replicate?
Granted, those Paduano frames are very sexy, but if you paying that kind money, I would get it fitted.
I agree with dalava. Unless you have a frame that fits where you can calculate stack and reach, then knowing it for a random frame is meaningless.
But OP...if you want to calculate stack and reach for say a 560 effective top tube (horizontal dimension) and 595mm seat tube and 206mm head tube, I can help you out if you establish BB drop. We could even pick some general nos. if you can't dig out what you need which isn't always easy without contacting the mfr.
Like BB drop = 70mm
Fork rake = 45mm
Fork length crown to axle center = 375mm
But this stuff sometimes isn't published. For example fork length generally isn't. Fork rake also isn't published always. Don't see it for the Domane for example. Roubaix as an example has a 49mm rake to reduce the trail of the bike to increase steering sensitivity...steering is slowed by long wheelbase (chain stay length a contributor) and 73 deg head tube angle which gives the bike is great ride quality. More rake to the fork which decreases trail also improves compliancy.
The Domane which is a similar bike to the Roubaix has a very different geometry with more BB drop which increases its stack height for the same head tube length. Stack partly came into being because most presume that by looking at head tube height they can determine saddle to bar drop...but this is a false assumption because seat tube length starts at the BB center and why stack starts at the BB horizontal center as well.
I will tell you what I believe is a pitfall of a custom geometry if you absolutely don't need it.
1. Unless you do the trig just right and nail every parameter, you won't achieve a 0 spacer stack height and slam your stem which is your intent. Also you lose some adjustability targeting this design condition.
2. A frame's ride and handling are a function of all frame dimensions. A custom builder has to be a sevant to nail both and also read your mind as to what you want. This is why picking a production frame close to your requirements is your best bet by a fair margin. Hope that makes sense.