Anatomy of an inline skate wheel.

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Inline skate wheel durometer.

Inline skate wheels are spun-molded from polyurethane, their hardness can be measured in an industry scale known as an ‘a’ rating. 75a being very soft and 90a being very hard.
There are pros and cons of having very soft or very hard wheels.
Soft wheels absorb vibration well. Hard wheels don’t. Learn to bend knees and use them like springs to help counter effects of vibration.
Soft wheels will wear down much faster than hard wheels. Wheels are expensive too!
Soft wheels will grip the road better than hard wheels. That’s because the weight of your body pushes down more wheel rubber into the road creating more traction.
Soft wheels are slower than hard wheels. Yep! For the same reason. The less material in contact with the road, the less friction and rolling resistance. Speed skaters tend to use much harder wheels than recreational skaters.
Most recreational skates have a medium compromise of about 75a hardness. We reckon that’s a bit soft. The manufacturers want them to wear out and then you need to buy new ones. When you do need to replace them go for about 83a, they wont feel too hard and wont wear as quickly. Rotate your inline skate wheels regularly to wear them evenly.

Inline skate wheel size.

Inline skate wheels come in various sizes which can be seen written on your wheels in mm.
Different wheel sizes have different characteristics.
Small wheels tend to let your skates be more maneuverable. You have a lower center of gravity and the distance between the point of road contact between front and rear wheels is short.
Aggressive skaters, hockey players and slalomers tend in general to like smaller wheels.
Larger skate wheels tend to be faster and smoother. (Once you have accelerated) They offer the least rolling resistance. Big wheels ride over bumps better.
Larger wheels offer a higher center of gravity and so feel less stable. Improved technique and balance are required to counter these effects.
Recreational skates tend to have wheels between 72mm and 80mm or perhaps a mix of two sizes. This is a good compromise between speed and maneuverability.
Be careful buying larger wheels for your skates. They may not fit in your frames.

Inline skate wheel profile

… Or the side view. What’s important here is how pointy it is. The wheel above has quite a blunt profile. It will offer a lot of traction and stability because it has more material in contact with the ground. A ’sharper’ wheel will be less stable but will be faster for the same reason.
This is only really relevant on new wheels. Soon you will wear them down to a happy compromise so dont fret too much.