Originally Posted by
guadzilla
The ETT figure gives me approx reach - yes, this is going to be affected by the STA and, to a lesser degree, the HTA. But as mentioned in my post earlier, the variation caused by STA is typically manageable in terms of setting up the bike to replicate a particular riding position.
ETT doesn't give you meaningful reach, since the STA effects it quite a lot... in addition to HTA and HT. Most people don't realize that HT length effects reach on two frames that otherwise have the same STA and ETT. That's one reason why "stack" and "reach" are not so great for sizing. A 30mm HT difference is ~10mm in reach. And as you mentioned there is a huge amount of lateral adjustment possible in seatposts, saddles, and stems. So long as you can achieve your fit with normal components, all is well.
There really is no substitute for figuring out where you want your saddle and bars relative to the bottom bracket, and then breaking out the HS geometry book and seeing what it will take to connect the dots.
For instance, I'm 6ft with average proportions, but like a lot of drop from the saddle to bar. Because this is "unusual" it is the controlling factor in sizing. I ride a 54cm frame with a 145mm head tube, 130mm -10 stem (no spacers), and 20mm offset post with the saddle back about as far as it will go. If I didn't want so much drop I could ride a 56, 58, or even a 60 quite easily.