I've been running 195/50/15 on all four corners for the past 80,000 miles. And I drive my smart bloody fast.
So far as I can tell, here's what to expect:
- Incredibly reduced understeer. I'm talking your car can handle like it's on rails. You could actually pull pretty good times on autocross.
- Oversteer! For drifting, of course.
- Highway stability. Seems to hold its line so much better than it did with the factory size.
- Can rotate tyres (provided you have four equal size wheels). I have staggered wheels, but equal tyres.
- Price. I've found it so much cheaper to ditch the irregular factory sizes.
- Looks. IMO, I love how wide tyres on a smart stick out like a little racecar.
- Rougher ride if you go for 195/50/15. As some folks like myself, chumly, and others found out, the smaller profile you go, the bumpier things get. It's not too bad, but definitely worse than stock.
- Snow traction. It seems to me that staggered smarts handle snow better than equal size on all four. Your mileage will vary as snow traction is a HUGE gray area with too many variables to draw a single conclusion from.
- More weighty low speed steering on cars with manual steering. Ignore this if you have power steering, but if you have manual steering like I do, your wheel will get a bit more hefty. I see it as a pro, I like my steering to be heavy. Though some don't like that...