General Cycling Discussion - mtn vs road bike fit

I've been on two wheels for as long as I can remember. But it seems all my bikes have been of the flat bar, nobby tire, lotsa reach and elbows out variety. Recently I saved and mid 80's Schwinn road bike from a co-workers "to the dump" pile and after some metal polish on the shiny bits and new rubber I just took it for my first spin around the driveway.

First impressions are...um....compact, that would be a good word. Standover is good, But the TT length has me wondering. Looking at pictures of roadies in action make me feel like I'm postured appropriately(its not uncomfortable or anything), but its just so weird feeling. Is there a transition period for this weirdness? Will I get accustomed to it eventually? Is there anything I should look for to make sure the frames not too small for me?( don't want to plug alot of dough into something that'll cause problems down the line)

I hope to make this my commuter/weekend warrior soon so I can re-makeover my mountain bike to dirt only again.

There are certainly differences in the riding positions of mountain and road bikes but you didn't give us enough information. How tall are you? What is you inseam length. How much clearance do you have when you stand over the top tube? What size is the Schwinn? If you can provide that information we can probably come up with a ball park guess for fit. A picture of you sitting on it would be good too.

If you're like me, and the frame's too small for you, your lower back will start hurting within half an hour or less. ;)

That being said, after figuring out my own fit on my road bikes (the two I have with drop bars), along with the recent hybrid and newest MTB, the saddle-to-handlebar distance on all of them is nearly identical to my MTB that I got in college (and I picked that one after trying out three sizes of one bike model). Specifically, since I ride the drop bar bikes most often with my hands at the hoods, which adds about 2" beyond the handlebar clamp, that's the distance that I measured -- and I didn't even measure them until I got them comfortable for ME.

Frankly, I was surprised. The riding position of each bike definitely feels different, and the drops give me a more aero option, but I can't think that it's just coincidental that every bike measures 30" on the nose.

I'd say to check that distance to see if you're in the ballpark with the ol' Schwinn. On your flat bar bike(s), measure from the middle of the saddle to the handlebar clamp; on the old roadie, measure from the middle of the saddle to a virtual line that runs between the middle of the bars where they point forward (basically, about where the brakes clamp onto the bars, or maybe an inch rearward from that point).

If they're within a couple inches (at most), you're probably going to be fine. If it's a bigger difference than that, you'll feel it, and it might hurt after a long enough ride.