So I bought an '84 stumpjumper a couple months ago. Completely stripped it down, rebuilt what was needed, replaced a couple things here and there, and replaced the flat bar with a drop bar. The idea was to make a touring/utility bike on the cheap.
The geometry is pretty relaxed, as you would expect, but the handling seems weird to me. When I turn the bar slightly at speed it responds “normally”, but if I do any kind of sharpish cornering at lower speeds it feels like the wheel is trying to pull to that side. I get the same thing when I stand up to pedal and jerk the handlebars back and forth a little bit. It’s not really a huge deal, but I sort of have to fight it when I ride this bike.
I could also describe it as the handling changing depending on how much I turn the bars. Sort of like it’s very stable/untwitchy at shallow angles, and really twitchy as the angle is increased.
I’m not sure if this is:
normal for a bike with geometry like this
a result of switching to narrower drop bars
something that could possibly be corrected with a fork that has shallower rake
Your hands and body weight are much farther forward over the front wheel. I would suspect this. Messing around with aerobars on a road bike you can really feel this effect.
Sounds kinda like the effect when you put a too long fork on a bike, -> too slack head angle. A '84 Stumpjumper will likely have quite a slack head angle, and when you put more weight farther away on the stem (drop bar) it’ll do that. Sorta like a pendulum effect, the heavy bars and heavy front wheel swiveling around too far forwards on the headset, if you get what I mean. Shorter stem will probably help (less of leverage, kinda), or maybe even a shorter fork or one with less rake.
Just my .02 based on building frankenbikes like that.