Clydesdales/Athenas (200+ lb / 91+ kg) - Need help fitting a bike.

So I tend to ride bikes on the larger side (61cm & 63.5cm frames at the moment, the 63.5 is a little big), and I'm wondering what the smallest size bike I could reasonably comfortably ride would be. 6'2" / 30" inseam / 34" standover height.

I want to get a loaner bike that I can let friends borrow for rides (since most of them won't fit a 61cm frame), but I don't want to have a bike sitting around that I can't ride on occasion without looking like the bicycle version of this guy:
http://www.utahmotorcycleriders.com/Pictures/crazy_fatguy-littlescooter.jpg

Any suggestions for how small I can go?

I'd get a 61cm frame for you, and get a really short stemp and lower the seat for when friends come over. If anyone should be uncomfortable it should be the ones borrowing the bike, at least that is what i expect when i ride something that is not mine.

I am 6'2" with a 31/32" inseam (jeans, sorry i dont know the exact biking inseam). i ride a 2005 Trek 1200 that is a 56cm frame which is definately on the low end of our comfort range. ideally, i should be on a 58cm but the deal was too good to pass up. my stem is at a 45 degree angle and that helps with my reach a bit.

It would seem that you riding a 63cm frame would be enormous to the point where you couldn't even reach the ground. doesn't seem that safe.

hope this helps

you need to make sure your comparisons are apples-to-apples, so I'd focus on the TT length rather than the frame size, because there's huge variability out there.

I ride a Kona Kapu, it's a 58 (or a 59), and the TT is 59 and change. My buddy, who is a little taller than me, rides a Madone which is a 60...and his TT is shorter than mine.

That said, based on your proportions -- I'd say you could go 58 in a traditional fit with no real issues.

What changes are you willing to make to adapt the bike to yourself, or your guests?

I would say that I'm close to average-sized (5'9" in socks, with a 32" inseam). I own two road bike frames that fit well: a 56cm with "traditional" geometry (= horizontal top tube) and a 54cm with "compact" geometry (= sloping top tube). A 56cm compact frame is ridable, but doesn't feel quite right. Haven't tried a frame with a horizontal top tube recently, but the last time I did standover height was a bit of an issue on 58cm frames.

In order to accommodate both yourself and your guests, you might think about swapping stems and seatposts. No-name stems and seat posts are pretty cheap... Shorter folks would use a shorter stem and maybe a zero-offset seatpost. You would use a longer stem, perhaps combined with a setback seatpost. You could also leave the fork a bit long and move spacers above/below the stem as necessary. All of these changes can be done with 4 and 5mm allen wrenches in the space of a few minutes.