Scooter wheels are available in a number of sizes. The most common sizes are 100mm and 110mm. This is measured from the opposite edges of the tyre.
The tyres are usually made from a compound known as PU88. This is a type of Polyurethane that moulds well and grips well. The material also dampens noise and a bit of vibration making for a nicer ride. Tyres are often black however it is becoming more common to have brighter neon colours and even a marble effect of 2 colours.
Wheel centres known as 'Cores' come in plastic or alloy. Alloy cores are most desirable due to the cool designs and vibrant anodized colours. The cores run on a sealed bearing. Most scooter bearing are made by the bearing company ABEC. This company has been making this size bearing for skateboards and roller/inline skates for years. The bearing is pressed into the core and can be replaced when worn if needed.
Due to the harsh nature of the sport wheels do wear out, tyres if skidded will wear flat spots on them and will eventually wear down in size. The good news is that scooter wheels are fairly cheap between £5-£15 per wheel which isn't bad given the amount of hours they will last.