BMX Bikes: for acrobatics, jumps and monkey around your neighbourhood, also off-road racing on obstacle course.
1 speed: for traveling short distances in a mostly flat neighbourhood. If you can walk there in 30 minutes, it should take around 6 minutes by bike. Not good for going up hills, even low grade climbs are hard. - Derailleur:
Tires 20 x 1.75: medium width tires with small thread, for comfort on asphalt and occasional off-road.