Ok so How do you fit a MTB? I am a roadie and I know what I like there but I am unsure how to properly fit a MTB. I am 5'10" with a 31.75" inseam. Last MTB I had was a 2001 Giant XTC SE2 17" which I didn't ride and traded for a bike for my wife. Now I want a MTB again (read I shouldn't have traded the XTC but oh well). I think the XTC fit ok but I didn't ride it too much so I am not overly sure. My Marin Mill Valley is a 17.5" but it is a roadie. What size do I need? The top tube lengths seem WAY longer than roadie TT numbers so it is throwing me off a bit. So one of the bikes I am looking at is a Surly 1X1 but I dont' know weather to get a 16" or an 18". The TT of the 16" is 10mm shorter than my old XTC and the TT of the 18" is 10 mm longer.
Should I go with the 16" and a longer stem or the 18 and a shorter stem? Thoughts?