A bit over 180km/h on a 1981' Suzuki GS650 Katana
Apparently it was originally capable of 200km/h, which was my goal. It was still pulling hard at 170km/h when a horrifying weave developed. The bars flapping from side to side rapidly and uncontrollably, and the rear of the bike swinging from side to side, stepping out half a meter at a time. Known as a tankslapper among riders. The terror of a tankslapper can not be expressed in words.
I hoped the handling might fix itself at a higher speed, but it only got worse as I got faster. It seemed certain I was going to highside (where you get thrown from the saddle and land in a sickening crunch, as opposed to lowside, where the bike relatively gently slides out from under you).
I drifted across three lanes and eventually managed to slow. I was extremely shaken by this and began to laugh histerically.