Vulcanman500 let me ride his vulcan a few times. I have let vulcanman500 ride my kz650. Next thing I know, he buys a cbr600f hurricane. Yes, he let me ride it. I don't honestly think either one of us would let anyone else, though. Furthermore, I'm trying to envision the scenario where anyone would want to. I think all the non-riders we know are scared of our bikes, to be perfectly honest.
You know, bikes are so personal and unique, I think ownership is the only sure guarantee of proper caution,,,besides, my bike has the fairly common UJM "quirk" about first gear, sometimes, after a stop. If you don't go to neutral and release the clutch, then reapply and shift to first, occasionally it feels like it's in, until you get about halfway into the intersection, and it pops out! I don't think I want anyone else to experience that on their first ride on my bike, especially a non-rider trying to learn! In a slow turn, the sudden loss of power can be a little sporting

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