Hi Jim,
I sold my chrome alloys (a bit much for me but looked kind of cool) and replaced them with the rear size stock steel wheels with the 175/55 R 15 tires. Even bought the factory hubcaps from the Pure (really plain but believe it or not, they really look nice on a white/silver Passion). Can't believe the difference on the road. All the "nervousness" is gone and sidewinds are no longer a concern. Corners well, and I corner aggressively, using the gearbox as fully as the gearbox on a smart can be used. It's no Mini but it is much, much better than stock. I grew up on rear engined cars so I'm used to tail happy vehicles but the smart so far hasn't shown that side of it's character. The standard fronts understeered way too much - I guess Mercedes wanted you to run off road front first rather than rear. I try to avoid both extremes. Enjoy the switch and yea, check out my friends at SmartMadness. They're the best!