I only used pounds because the table the user above shared was in pounds. And comparative damage is just that: comparative. It's the fourth power of the ratio between the two. So keeping to the same units was easiest.

Regarding the rest of it, remember we're comparing it to a "freakishly heavy bicycle". The table the other user shared implies a fat man + bike is 350 lb. My assumption was that's 300 lb person + 50 lb bike. That would be a 23 kg bike. That's crazy heavy. It's more than double most bikes' weight, and triple the weight of a racing bike. So if the motorbike weight I used is an overestimate, that's basically just evening the playing field. (While both will still end up looking worse compared to a car than they should—which just highlights how much better both are than cars.)

Anyway, I got the figure by just Googling "motorbike weight", which turned up this page, which says:

Some sources say the “average” motorcycle weighs around 700 pounds, but the weight depends on the brand of the bike, the engine size, and the style—whether it’s a street, off-road, touring, cruiser, or sport bike, or something else entirely.

I'm not interested in being precise enough to delve into those different factors, so going with the quoted "average" sounded good to me.