RE: [rootsradicals] Big Dummy sizings and brooks saddle mounts.
I am 5’8” with an inseam of 31” (both measurements with bare feet) and I have a 16” Big Dummy. I have had it for at least a year now and love it. Originally my impression was I should get an 18”, but when I actually ordered it from Xtracycle they only had one Big Dummy left in 16” and they were quite confident it would be appropriate for me to use. I have always found the guys and gals at Xtracycle provide exquisite advice and customer service, so I went for the 16”. I have no regrets.
I should mention my previous bike was an Xtracycle equipped/extended Univega 750-FS (This is just a stock photo I found on-line, but it gives you an idea… http://www.bikepedia.com/Images/image.aspx?filename=FS-750, 9006.jpg). As you can see from the stock photo the top tube of the frame starts going back to the seat post tube from a little bit down the top tube rather than from the head tube. Therefore the top tube of my old bike always felt lower that anyone else’s bike I tried riding on, but I LIKED it that way. It gave me more clearance when mounting the bike and sometimes when I stopped and did not want to stand on my feet I would actually rest a thigh/buttock across the top tube, which would allow me to stretch out my other leg as it acted as an upright support. When I saw the Big Dummy was released with a slight dip in the top tube I was very happy with their design choice because it somewhat mimicked my old frame.
As it is with the 16” frame I would believe now it is definitely the right size for me. I do not think I would have enjoyed an 18” frame as much. The slightly lower center of gravity also probably provides a little extra stability and easier handling as well. It is difficult for me to account for torso height versus top tube frame length because I always like to use Nashbar Trekking bars (http://www.nashbar.com/bikes/Product_10053_10052_175533_-1_200303_200276_200388) or similar handle bars. These allow me to position my grip forward or more upright depending on my mood, and I also mounted them in such a way that allows me to actually drop down with my elbows cradled in them for a more aero-position for descents and sprinting, etc. (as much sprinting as could be done on an Xtracycle/Big Dummy rig of course). In any case, I mention the handle bar style I use because I probably could not offer a good judge of top tube length comparisons. However, as far as height I can vouch for a 16” Big Dummy frame for my height and inseam.