Wheels per package:
The amount of wheels in a package. A scooter needs two wheels, one for the front and one in the back. When your wheels are close to being worn down it might be an idea to consider buying some new ones, before it is too late.
Each wheel needs 2 pieces of bearings, which have to be pressed into the wheel if not already included. The quality of bearings is divided with ABEC. The higher the value, the better the bearings will run. For an example an ABEC-7 is better than an ABEC-5.
The size of the wheels should depend on the way you ride. If your focus is a great experience, a sweet flow and nice speeds, then you need to go for larger wheels. If instead, you want fast reactions and improved control, then you will need to go for smaller wheels. It is important the wheel diameter fits along with the fork, deck and brake.
The total weight of the wheels once assembled. Lighter wheels is a good idea if you want to do tricks with your scooter, however the durability lessens on lighter wheels compared to the heavier ones. Heavy wheels will therefore last longer, but the execution of the tricks will also be harder.
Wheels of aluminum and nylon both has their advantages when it comes to quality. Wheels of aluminum are the strongest, but nylon wheels are the lightest. It is therefore smart to go efter nylon wheels if you wanna perform tricks on your scooter. If you on the other hand is using your scooter as a transport then aluminum wheels is the choice for you.
There is various types of core designs: Solid and spoked. Solid core wheels are relatively heavy wheels, but at the same time more durable. Spoked wheels are lighter, but have slightly less durability.
A wheel's hardness is measured on the durometer scale, which goes from 0 - 100 A. 0 is the absolute softest while 100 A is the hardest. Hard wheels lasts longer and rides faster. Soft wheels wear down quicker, but has a much better grip and are perfect for parks and indoors usage.
A flat profile gives the best grip, where as the most narrow profile provides more speed for the wheels. The fork's look needs to match the wheel profile.
Wheel hub width:
The vast majority of scooter wheels have a hub width of 24 mm, which fits forks and decks with also 24 mm hub width.
Describes the diameter of the axle / bolt that will hold the wheel. The wheel in the ball bearings is intended for a specific diameter of the shaft / bolt.