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Flopping? Hub knackered, badly setup steering linkage (most shops/retailers do not know how to set these, its a huge issue and causes the bike to handle like shit or just dangerous, R+M have same issues with dealers not doing the job right), play in one of the headsets etc.
Ridden 10k miles now between 2 bullitts in 5 years (so low mileage compared to couriers) and in that mileage only had to replace 1x headset bearing, and both had smallest amount of play in ball joint (about the same as the play that R+M and Omnium get in their ball/rose joint after 1000-2000 miles). Never had speed wobble, its almost exclusively caused by the above factors**Flex in frame causes steering geometry changes in all cargo's that use a metal rod for steering. This is why some brands like Douze utilise push me/pull you cables for steering.
I don't think so, I think that's 10,000W. If he's being truthful and it can go up to 50mph. Looks like a beast!