Facts and Friction
Depending on the size of your wheels, your wheel bearings spin at about 800 RPM at 60 MPH. That’s 800 revolutions in the minute it takes your bike to travel one mile. While that’s nowhere near as fast as your engine bearings spin, it’s still fast enough for friction to generate some serious heat.
And, unlike engine bearings, your wheel bearings do this while carrying a substantial load – the weight of the bike plus the weight of the driver.
Normally, with help from a little lubricant, wheel bearings manage to handle this kind of load in stride without letting friction turn up the heat. But the bad news is that, unlike riders and fine wine, they don’t get better with age.
The Steel Bearing Lifespan
You can typically count on motorcycle bearings to last anywhere between 20,000 and 100,000 miles. That’s a pretty big variance. Within that 80,000-mile difference are considerations for riding conditions, riding style, and care and maintenance. Obviously, if you weigh 90 pounds, keep your speed under 60 MPH on the smoothest and driest of roads, and keep your bearings lubed and maintained regularly, those bearings are going to last you longer than if the opposite situations apply.
Steel ball bearings may appear completely smooth, but so does planet Earth when you see it from the Moon. Were you able to explore a steel ball bearing at the same scale as Earth (such as with a microscope), you’d find that their surfaces are actually pretty similar.
There are mountains and valleys, and variations in roundness that may not be apparent, but they are there. And you can be certain that these features generate friction. But that’s not all.
Ball bearings work by rolling between two steel “tracks” known as races. Those tracks have the same kind of surface as the balls, which can wear down over time. Think of it like a path through a field. If you walk or ride on that path every day, eventually it’s going to wear down into a groove. The same thing happens with steel races.
As the races wear down, the gap, or “play” in the bearing increases, which also increases friction, and therefore heat. High heat causes the ball to weld with the races on a microscopic level. These welds are instantly broken by the momentum of the wheel as it turns. These micro-welds are impossible to detect with the naked eye, but they build up over time, amplifying the topography of the steel balls and exponentially increasing friction and heat.
Eventually, small pieces of the steel ball will fracture off, adding grit to the inside of the bearing that will rapidly hasten the breakdown of the remaining balls and soon cause the bearing to fail completely.
Don’t worry, a rider will almost certainly notice issues with their wheels well before their wheel bearings reach the point of failure, but it’s important to understand the breakdown process so you can remedy it.
The Best Remedy
Unsurprisingly, just as in medicine, the best remedy is always prevention. Careful, regular maintenance will almost always extend the life of a wheel bearing. This means cleaning and re-lubricating them frequently, especially after exposure to moisture or submersion in water.
But prevention can also mean replacing your steel wheel bearings with quality ceramic bearings.
The difference between steel and ceramic ball bearings is pretty huge.
For starters, ceramic ball bearings are about four times smoother than their steel counterparts. This means far less friction, and therefore less heat. But even with substantial heat, the ceramic material (usually silicon nitride) is non-conductive, and therefore highly resistant to heat.
Ceramic bearings also have steel races (we call them “ceramic hybrid bearings.” We also offer full ceramic bearings with ceramic balls and races, but they are not recommended for use in motorcycle wheels), but the extra smoothness of the ceramic balls causes far less wear to them. And since the balls and the races are different materials, the balls will not “cold weld” to the races, further eliminating the primary cause of bearing breakdown.
Ceramic hybrid bearings are usually more expensive than steel options, but they will almost certainly last longer, which basically covers any difference in price. What’s more, ceramic hybrid bearings PERFORM better, attaining higher RPMs and better fuel economy than even the best steel bearings.