It looks like you're not really attempting to compare your Vulcan experience with a car tire to the Spyder. It's really, apples and oranges. Putting a car tire on a vehicle designed for a motorcycle tire (Your Vulcan) cannot be compared to putting a car tire on a vehicle designed for a car tire (The Spyder). Obviously, your Vulcan is designed to lean, and a car tire is not designed to ride on the outer edge. Whereas, a motorcycle tire is specifically designed to do just that. Still, cupping has more to do with balance and worn suspension components than it does with the vehicle it is fitted to.
Your Vulcan was designed to lean. And while the Spyder body does lean. The suspension keeps the tires level (or attempts to).
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The next issue you run into with a car tire on a motorcycle rim is the rim bead/seat area matching the tire bead/seat area. It doesn't. Of course, since the Spyer has a car rim/wheel, fitting a car tire to a Spyder wheel is a perfect match.
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