I'm considering buying a 2012 Devinci Silverstone SL 2 second hand. Size is Small, 52cm.

I used several calculators online to estimate what size frames would be suitable for me and came up with several numbers.

This frame falls within the more aggressive fit which I think I'm okay with. But would still like to run by the forum here for approval.

However, what I don't understand is the numbers this calculator gives me regarding saddle setback. Most saddles allow for 10mm offset from center in either direction.



The calculator suggested a seat post with zero offset (!) and a 50-56mm setback. I know calculators are always wrong, and I will be making the minor adjustments myself, but I'm using this as a guide and I just don't understand what it means.

How could I get a 50mm setback with a zero offset seatpost?

The bike has a 25mm setback seatpost, by the way. And the stem is 120mm - 15mm longer than suggested by that calculator, (but on this type of fit, wouldn't an extra long stem such as 120mm be suitable? So the calculator is wrong in that sense, almost definitely, as per my understanding of how pros fit their bikes. Not that I'm a pro, but if I go for this bike/fit, it will be following those trends.)

Thank you very much.