I think the difference has a lot to do with rake angle. The taller the fork, the more effective rake angle. The newer bikes are designed with a rake angle that complements the standard travel fork of the day. Which these days is a pretty long travel. Captain America’s Easy Rider Harley had an increased rake angle added to the frame and extended fork tubes. They say it steered like crap. Basically, the front wheel wanted to flop to one side when the handlebars were not held.
