My main bike is an 80's Concord New Yorker. I'm 5'8, with a 30.5" inseam. The bike's seat tube and top tube are both 21.5", with a 30.5" standover height. The bike fits me fine; the frame is basically an exact replica of the old diamond-frame English 3-Speeds (Raleigh, Phillips, etc.). It has ISO 590 wheels (same thing as 650A), so they're bigger than standard 26" MTB wheels, but smaller than 700c road bike wheels.

The thing is, I have developed a slight obsession with this brand. I got this bike for $25 and it has blown away anything else I've gotten my hands on. Through doing some research I've discovered that Concord made a few other models in the 80's, including a hardtail MTB and a few 700c Road bikes. I'd like to get my hands on both of these, but obviously I'll likely have to resort to something like Ebay, where I'll have no way of trying before buying.

Unfortunately, I don't have much experience with either of these two styles of frames. And what's more, I realize bike geometry has changed during the last few decades, so just because I can go to the LBS and find something that fits me, doesn't necessarily mean it'll hold true for an 80's bike. However, I'm just looking for a few GENERAL rules here.

It seems to me that since a MTB has smaller wheels than my New Yorker, I'd want a slightly larger frame to compensate for it, correct? I know that when I ride beach cruisers, which have standard 26" wheels and always seem to come in 18" frames, things always feel a little cramped compared to my Concord.

And would it be the opposite for the road bike? Because the road bike has larger wheels, if I didn't choose a smaller size frame, wouldn't the standover suddenly be too high? (as it is on the New Yorker I have 0 - .5 inches of clearance).

Thanks in advance, like I said, I'm very eager to build my stable of Concord's !