corrado33

I ride a 54-56 cm road bike. I ride an 18-19 inch mountain bike. Converting both to a reasonable system of measurements... that's 54-56 vs. 45-48 cm. I have a couple of questions.

Are top tube lengths of road bikes relatively shorter (compared to the seat tube length) than mountain bikes? So Road bike TT/ST < Mountain TT/ST. They would have to be to fit the same person, right? Is the reason seat tubes on mountain bikes shorter because we like to get the saddle out of the way when we're riding downhill?

I mean, when we're pedaling to get the optimum efficiency our saddle to bb distance is going to be pretty much the same on both bikes. So, if you don't move the saddle out of the way (XC bikes?) could you simply convert a road frame to a mountain bike? (Theoretically, not practically, I'm not really interested in doing this.)

I'm asking this because I recently found a bike that's super cool, it's a 54 cm fully chrome bike, but it has mountain bike tires (wider 26s). My next thought would be to measure the TT, but then the thought after that was, can you compare TT lengths between road bikes and mountain bikes since road bikes use a bar that puts the hands 4-5 inches in front of the stem, and mountain bars put the hands pretty much at the end of the stem? The bike is from the 80s, where the line between road and mountain bike was blurred, so I'm really not sure how to tell if this bike would work for me or not. It feels fine, but most bikes do feel fine until you ride them a couple of hundred miles.