Joined: Oct 2011
Posts: 10,053
Likes: 2,508
From: Fairplay Co
Bikes: Current 79 Nishiki Custum Sport, Jeunet 620, notable previous bikes P.K. Ripper loop tail, Kawahara Laser Lite, Paramount Track full chrome, Raliegh Internatioanl, Motobecan Super Mirage. 59 Crown royak 3 speed
My guess is that is in the headset or maybe wheel bearings. If it is a wheel out of true enough to cause a wobble you would likely notice with your hands on the handlebars and at nearly all speeds. Basically a significantly out of true wheel would be noticeable the whole time your riding and not just under certain circumtances.