The core of the wheel is comprised of the hub and the spokes. The bearings and spacers are housed inside the inner hub. The spokes and outer hub are what the polyurethane itself is attached to.
The way the core is designed, and the materials from which the wheel is constructed are what give the wheel its stability. These same two things are also what give the wheel its strength. Aggressive wheels tend to have a solid core, while racing wheels tend to be lightly spoked. Your standard hub is generally called a 608 hub, meaning it takes a standard 608 type bearing.
The definition of profile is the wheel’s cross section where the wheel and the ground meet, as viewed head on. This profile is what determines the amount of wheel in contact with the ground while being ridden.
Per industry standards, all inline skate wheels are twenty four millimeters thick. However, it is the variation in your wheel’s footprint that provides your wheel with different functionality. The larger the wheel’s footprint is, the better stability and traction it has.
Selecting Your New Wheels
The hardness of the wheel and the size of the wheel are the two biggest factors, so you have to base the choice you make on these two properties. The core does have a significant influence, but it is more subtle. You will want to make your core and profile choices after you have decided on what hardness and diameter you want.
Choosing a Hardness
The harder your wheel is, the longer it will last, but the less grip it will have, and the more road shock and vibration you will feel. The average recreational skater will use wheels between78A and 82A. These ratings generally provide a good balance of grip and shock absorption. That said, you do not have to use the same amount of hardness for all the wheels on each skate. If for the first set of wheels you do use the same wheels all around, you will likely find that different wheels wear in a different pattern or rate. For instance, my wheels always wore the most under the heel, and graduated evenly up to the toe, which wore the least. The heel also wore flatly, while the toe wheels wore more wedge shaped. To combat this, you can use differing durometers of wheels to even out the wear.
Picking a Size
In general, wheels between 72mm to 80mm are appropriate for recreational or fitness skaters. Lighter skaters will find 72mm appropriate, while mid-weight skaters will generally want 76mm. Heavier skaters will want 80mm or larger. You will also want the larger diameter wheel if you plan to speed skate, are going to be going long distances, or practicing short sprints, something like 84mm or larger will be appropriate.
Just how large a wheel you can use is limited by the design of the skate, so you need to keep that in mind when purchasing your inline skates.