... it seems U.S. customers prefer the 16" wheeled models....
I'm one of those customers. As a GV250 aka Grand Dink / B&W scooter owner for the past 3.5 years I think the GV250 strikes an amazing balance between the feel and ease of handling of a "small" 100 - 150cc scooter yet offers the power and handling to do 75 mph+ on the highway. Great wind protection with a relatively "thin" profile that can still get between cars in traffic for California "lane sharing".
Complaints with 12" tires:
1. low ground clearance limits lean angle and thus turn speed.
2. I hit the center stand a lot - and I don't consider myself an "aggressive" rider.
3. pot holes especially when hidden at night practically knock the fillings out of your teeth. I find myself saying 'wow' wtf, after being surprised by one.
4. Tires wear out sooner [almost bald at 6K miles] - as the tire rotates more often due to small size and are a real pain to change - Think about getting a flat tire in the rear + the hassle of dropping the exhaust.
5. Limited suspension travel - means a very harsh ride.
6. Tire selection - lots in 16" think motorcycle, very limited choices in 12".
Ideal Tire Size?While I like 16" tires I don't necessarily need something that big but I want something bigger than 12". My ideal size is 14"+.
GV250 vs Burgman 400 and probably Yamaha Majesty
GV beats both for easy handling, lane sharing, off the line acceleration, slim non-bloated profile, outstanding smooth clutch / CVT operation - only vespa makes a slightly smoother transmission.
50mph+ Mid & top end:
The Burgman 400 & Majesty blow the GV away offering 90mph+ while providing as good or often better mpg and better high-speed handling.
Maintenance:
GV has some weak points - exhaust is a pain to reinstall and know to develop rattles and crack at around 10K miles. Air filter is unnecessarily difficult to change. Radiator - tiny hoses trap air and make expelling air after a complete change a nightmare and could overheat the engine if ridden on the highway while air is still trapped around the water pump.
PROS - easy to access and adjust the "screw type" two valves vs the nightmare of the Burgman's needless shim-under-the-bucket and the nightmare of Tupperware plastic to remove to access the motor.
GV's clutch lacks the various issues that the Burgman has had and offers better smoother operation. Based on two 2007 Burgman 400's I rode I feel the GV has a little less handlebar vibration.
I bought my 2005 GV used 3.5 years ago with 2600 miles now I have almost 16K. Only persistent problems have been - back light flickers and goes out on the speedometer display (only a problem at night) & exhaust has cracked repeatedly requiring me to weld it.
Final Note & Future Scooter:
I often ride my scoot 7 days a week - southern California = no rain and mild "winters". Day in and day out my scoot starts right up hot/cold/ damp or even once in a while in the rain - totally consistent like a modern car.
FUTURE - I believe 350 cc's single cylinder like the Piaggio BV350 is the ideal mix of power (for highway riding), high-speed handling, mpg and the all important thin profile that can slip through traffic while still offering good wind protection on cold days or at night. 400 / 500+ cc's brings undesirable bloat - width and weight, power that is rarely used or needed, poor mpg and makes the scoot too fat to get between cars.