Originally Posted by 3alarmer

...I've never tried to figure it out, but I have a lot of different 70's and 80's bikes I ride here from time to time, in rotation. Certainly you're correct that the biggest single difference is in the rotating weight of wheels and tires. That's obvious when you upgrade them.

But I'm not sure there's not some effect from where your center of body mass sits in relation to the crank spindle. So with a shorter top tube, tighter geometry bicycle, I end up putting it together with a different (longer) stem. And the steeper angles of the frame usually set the seat tube more upright. All of this serves to move my overall center of body mass farther forward on the bicycle. Thus you end up more over the spindle axis. Most people find this a better position for spinning higher cadences. But I admit I don't have any real science to back this up. And the overall effect might be more one of perception than actual performance.

I don't ride with a speedometer, it's too distracting.