i live in San Diego, the land of big freeways, and mostly use my bike as a commuter, so that means that pretty much every time I ride I'm up around 80-90mph. At about 90 mph the speedometer starts bouncing around pretty good!
I'm still on stock bars and I'm thinking I need to switch to clip-ons to get me in a better position against the wind. I was just wondering how many other people are high speed commuting with their 40yo bikes and how your bikes are setup?
Me! Regularly.
For bouncy speedo that might not be inside the gauge: look for a worn speedo cable, especially where it comes out of the drive box at the axle. They like to wear there, particularly when they were incorrectly set up to have too sharp an angle there. It is supposed to come out parallel to the fender stay, then curve gently upward to the frame and steering tree, no bends beyond that. Many times this angle is set up too sharp, then the cable wears out inside the fitting.
Also, take the speedo drive off the wheel and either disassemble and re-lube it with new grease, or at least put a little oil in there to soften up the old grease inside. Make sure the flat plate that drives the gearbox is also centered on the front wheel: sometimes these get assembled off-center a little bit, which makes the cable vibrate, which affects the speedo....
I ride behind a Vetter. Many don't like them, but I won't ride without one after 40+ years with it. At 105 MPH the windshield starts to fold over a little bit, but unlike the early ones (before the 1974 DOT-approved versions) it doesn't come back far enough to touch me in the nose!
And in crosswinds, rain, snow, sleet, hail, or bird-bug attacks, it is my best friend. I just rode thru all but the bird-attack part of this last Saturday, going up to the top of Mt. Evans.
I recently swapped the countersprocket to 19T instead of the 18T that has long been there. It makes 5th gear into overdrive, with 4th acting much like 5th used to.