How large and how small a frame can you ride?
A very short friend has been looking for a bike. I pointed her to a very nice 50 cm Cannondale on Craigslist. 1985 SR1000, almost all '80's Campagnolo, beautiful condition, pretty pearlescent green. So she and her husband go, spend a bunch of time with the seller, who is an ex-racer, they try the bike, love the bike, for $250 it is theirs. I'm happy. But now I wonder.
For her, the bike sounds a touch too big. They have to slam the seatpost, enough that it doesn't clamp securely (an aero Chorus post, I think). Hmm. Well, she can still straddle it, and the pickings are very thin for quality, pretty, cheapish road bikes, so I think it is okay. When your bike inseam is 30", things are tougher.
But the weirder thing is, they are thinking that this might be the husband's bike. He is 6' 0" with normal proportion legs and torso. They put the post all the way up, and supposedly the bike fits him great. The seller tells them that racers ride small bikes, because big bikes are wobbly.
I was befuddled. How, I wondered, can a 6' 0" guy be comfortable for more than a short ride on a 50 cm bike?
So, that got me thinking. Another friend once sent me a photo of his fleet, showing that he was comfortable riding anything from a 52 cm to a 58 cm. Hmm. I usually ride a 58 cm, but my measurements suggest that 56 cm is ideal, I have happily commuted on my daughter's 52 cm, and I've ridden up to a 59 cm. So, maybe we can ride a much wider range of sizes than I might think?
Or, maybe for short distances in peaceful circumstances, we can ride a wide range of sizes . . . on the 52 cm, when honking out of the saddle my knees hit the bar ends, and on the 59 cm, if my foot touches down on a low spot in the road I receive a "private" reminder.
What do you think? What is the range of sizes that you can ride, or that you like to ride? Is the limiting factor vertical (leg extension) or horizontal (torso-arms)? How much can you compensate using stems and set back posts?
And - for those of you with both a vintage roadie and a modern, briftered, carbon race bike - what is the difference in frame size between the two, if any? Are your touch points different? If you ride a 58 cm oldie, would you ride a 50 cm newbie?