Originally Posted by
Muirenn .
I emailed Soma, hoping for stack and reach, and they told me to look at effective top tube only, and go up a size if I want to be less aggressive. (I would say I'm more comfortable in a more aggressive position, but don't intend to race. Not anytime soon, anyway).
Well, my Pinarello Quattro fits well, its number are:
Quattro: 51.5 Size Seat Tube 53.5 (c-t) Top Tube
53.5 (TT) (This is actual, the only one listed. Stack 53.1 (S) Reach 37.8 (R) Head Tube 13.0 (HT) Head Tube 72 Angle (HT°) Seat Angle 73.7 (ST°) Chainstay 40.6(CS) Setback 14.5 (SB) I use a 110 mm stem with a zero offset seat post due to high saddle height (73 center of bb to top of saddle) and inseam torso ratio. Need the zero in most bikes I ride just to barely get over the pedals. I was thinking 48 or 50. Any suggestions? From some of the comments, it sounds like 50 will be too big, but the 50 has the same actual TT as my Pina. I'll bring the measurements to my fitter, but he is an engineer, and the numbers are a little sparse.
Here is the chart again.
I believe that you are mis-interpreting the "geometry" for the
SOMA Double Cross frame ...
You need to ignore the "actual" TT length and focus on the effective (
aka "virtual" or "level") TT length ... which means that the
48cm SOMA DC frame whose virtual top tube is
540mm is probably the better frame choice since I'm pretty sure that your Pinarello has a "true" (
as in, non-sloping) horizontal top tube.
FYI. If you were to set up the Soma DC with the same number of spacers between the stem & the headset then the stem & handlebars will probably be significantly LOWER than the relative differential between the top of the saddle & the handlebars on your Pinarello and you will probably find that you will want a shorter stem ... probably a
100mm will be the right length
; but, possibly a stem as short as 90mm-to-95mm.
Wider handlebars could result in the need for a shorter stem, too.
FWIW. I have several bikes whose frames have vastly different sizes ... although there was a period when I was experimenting, with the exception of saddle height above the BB & the saddle's set back, I would say that all have ended up being set up essentially the same as what I was riding decades ago! Of course, that probably means that I got more lucky than I should have as far as setting up my earlier bikes ...
Basically, to ensure continuity between
my bikes ...
- first, I establish the relationship of the saddle to the cranks -- this is regardless of the crank arm length & it isn't a "fixed" relationship to the spindle
- then I measure from the middle of the REAR edge of the saddle to the rear of the horns on the hoods regardless of the width of the handlebars or the height below the top of the saddle
When I get the measurement to within about an inch, I generally stop tweaking the fit ...
- variables include handlebar width, bend, etc.
The result is that 'I' don't notice when switching between bikes since my upper body is essentially at the same angle (
probably within ~1º) & the angles of my shoulders/elbows/wrists are essentially "the same."
To some extent, the frame size is (IMO) cosmetic ...
Regardless, the
rule-of-thumb in the past for CX frames is to size them ONE SIZE smaller than your Road frame (
presuming the Road frame is properly sized for the rider) ... where I believe that "one size" typically referred to an "inch" gross difference in the seat tube length (
a variable amount to the actual size difference depending on the seat tube angle) ...
Hence, the 48cm Soma DC has about
an inch smaller seat tube & it has a TT which is close in length to your 51.5cm (
the theoretical c-c) Pinarello.
- to state what may be obvious, a reason for the "one inch" sizing difference is to compensate for the higher Bottom Bracket which a CX frame will typically have when compared to a Road frame + the larger CX tire circumference & therefore to ensure that the standover height is approximately the same ...
BTW. While my FORT certainly "fit" me, my too-late realization was that I would have preferred a frame which was "one size" smaller & adjusted the fit accordingly.