Row, row, row your balls, gently down the inner race... I am going to pretend I didn't just say that.
The balls are the part of the bearing that do the rolling audible gasp!. Because of this, they are arguably the most important piece of the bearing. Furthermore, balls land center stage for the hottest debate in longboard bearings: Ceramic or Steel?
It is believed that ceramic balls are superior to the standard steel balls because they are stronger and smoother. Ceramic balls are significantly more expensive than steel balls, but this does not directly translate to a higher quality product.
There are 3 commonly used ceramics in ball bearings:
Silicon Nitride ceramic is the hardest of the three and most often used in ceramic hybrid bearings. It's important to keep in mind that "ceramic" only refers to the balls. The races remain chrome steel or stainless steel, hence the term hybrid.
Since only the balls within the bearing are ceramic, the outer and inner races are still steel. While the ceramic balls might be "harder" and "invincible against rust", the steel races can get rusted and pitted. This will greatly affect the feel and performance of the bearing. Race surfaces come in direct contact with the ceramic balls, degrading what higher qualities the ceramic balls may have offered.
The one advantage ceramic has over steel is resistance to corrosion, meaning rust. But remember ceramic skateboard bearings are hybrids; therefore the inner and outer races are still susceptible to corrosion.
It is possible to buy a full ceramic bearing at a price comparable to a skateboard brand hybrid ceramic bearing, but it will almost certainly come without seals. To get a fully sealed ceramic bearing, it will cost $200+ for 1 set of 8 bearings. You could get 10 sets of quality steel for that price!
Applications exist that specifically require full ceramic bearings, but the cost to use them in a skateboard just doesn't make sense. We recommend saving your wallet and going with quality steel bearings 9 times out of 10.
The only time we recommend going with ceramics is in a racing situation or if you just want high quality, regardless of the cost.
Steel is ductile and has elasticity that enables it to retain its original shape after loads are applied. It is also comparatively inexpensive with quality bearings going for $15-$25 per set.
The components in a steel bearing come polished smooth to minimize friction. Steel requires a lubricant to help the parts move smoothly under load and protect it from corrosion (rust).
There are some bearings that are made from stainless steel, but this is quite rare due to the high cost. If a bearing is low priced and claimed to be stainless steel, I would be suspicious if this is true. Most bearings are made from chrome steel.