Ever used roller blades or a skateboard? Not much fun when those little wheels jam on a pebble and throw you down is it? Well, the same applies to scooter wheels. Small wheels transmit bumps and jolts to the rider much more severely than larger ones do. The larger the wheel the larger an object it can roll over without ill effect. Larger wheeled scooters also seem to have a bit more ground clearance for cornering and a slightly larger contact patch on the road (Although some small wheels have obscenely wide tyres like the Yamaha Bee Wizz and PGO T-Rex).