Size is starting to make sense. I'd make the numbers farther from existing bike displacements though: up to 280, 281 to 560, 560 up. Yes there will still be bikes that are near the line, but fewer I think.
I don't have a problem with a single Thump as it stands.
"The belief that there is only one truth, and that oneself is in possession of it, is the root of all evil in the world."-- Max Born, Nobel Physicist