I converted an old Atala road bike frame to single speed/fixie. Didn't test ride the pre converted conditions, but now the back end is lighter and the bike seem unbalanced.

At moderate speed, perhaps 8-15 mph, the steering seem wobbly and I'm afraid to turn, fearing losing control. I've read Sheldon Brown's steering adjustment piece. Not sure if it's shakiness or stiffness or both. Is there a better description for both terms?

Is shakiness felt at low speeds?

I've made adjustments to tighten the threaded top race and backed off a bit because the handlebar became stiff.

Was wondering if the unbalanced bike, with the heavier chromlux rim front wheel has kind of a centrifugal effect to cause this wobbly feel. I've swapped wheel from a hi-tensile Univega bike and have the same problem.