Originally Posted by
usndoc2011
It would probably be fun to calculate the stack and rise for each bike, but ultimately inaccurate.
You can probably get fairly close. I tried it out with the Salsa Vaya, since they provide all the relevant numbersm including stack. I did it like this.
Let F = fork length
Let H = head tube length
Let A = head tube angle
Let B = bottom bracket drop
Let S = frame stack
S = sin(A) * (F + H) + B
Using the numbers for the 60cm Vaya
S = sin(72) * (405 + 215) + 75
= 664.66
This is in the ballpark of their published stack value, 660.7. If you calculated this way for all the bikes you're interested in, you'd get a reasonable basis for comparison at least.
Originally Posted by
usndoc2011
My main concern is the appropriate stack, especially since that is the value that isn't easily gleaned from published geometry specs, and since I'm not totally convinced that the reach is a more useful measurement of the effective top-tube (the steer tube to seat distance is probably more informative than the steer tube to an arbitrary point along the effective top tube line, which is pretty much determined by the seat tube angle).
The idea behind frame reach is that you're going to want to set your saddle in the same position relative to the bottom bracket regardless of seat tube angle. So for a frame with a slacker seat tube angle you'd move the saddle forward and for a frame with a steeper angle you'd move the saddle back, thus making the top tube length relative. Measuring reach relative to the bottom bracket accounts for this change in saddle offset and gives you an equal reference, independent of seat tube angle.
Originally Posted by
usndoc2011
BTW, for wheel sizes, this link has them tabulated
http://www.bikecalc.com/wheel_size_math. I'm not sure how accurate they are, since I got a number that was slightly off when calculating a BB drop distance from wheel radius and BB height, then again the tire size wasn't listed on the manuf site, so I had to guess.
There's generally some variability in tire depth relative to claimed size, so that might be the reason for the discrepancy. The table looks right.