If you spin a skateboard bearing like a Bones Red it will spin very fast and will go for a long time. This seems like a very logical test for a bearing. Below we explain why this is not the right test for a wheelchair bearing.
First, let’s agree on the goal of wheelchair bearings:
A wheelchair bearing needs to have the least rolling resistance possible for as long as possible, not in a single push but over the lifespan of the bearing.
This is true for both sports wheelchairs and everyday wheelchairs.
Before we can get into the test we should cover some “need-to-know” terminology in bearing construction. Essentially, a bearing is made up of balls, held together in a cage, placed between an outer and inner race (metal rings), lubrication is added, then seals (mostly rubber in the wheelchair world) are added to keep the lubricant from leaching or washing out.
Rubber seals work to keep moisture from getting in and stop lubricants from getting out. The seals are held in place by cutting a groove along the inside of the outer race and along the outside of the inner race of the bearings. The rubber seal is then popped into the lip or groove. A single lip seal means that the seal is held in place with a groove (lip) at the top. A double lip seal means the rubber seal is held in place by a lip both at the top and bottom. A double lip seal is way better for long-term bearing life than a single lip seal. The downside is that both upper and lower lip create friction in a free (no load) bearing, but have no practical disadvantage when someone is pushing in a wheelchair.
In this size bearing, the two most commonly used lubricants are oil and grease. Oil is by far the faster of the two, but the downside of oil is that it does not have water inhibitors and will leach out through humidity very quickly. In some climates, a bearing can leach all of its oil out in a matter of a week with no direct water exposure or in an hour with direct water exposure.
Then there is grease. Grease is thicker and harder to leach or wash away. It can have water inhibitors added to further extend its life. And - this is very important - grease will turn into oil at different RPMs (or heat), then will turn back into grease when it cools off. This means you can have all the longevity advantages of grease along with the speed of oil when you are using it.
Why Skateboard Bearings Spin So Fast:
Skateboard bearings are designed to be used in dry environments. You do not see a skateboarder go into a shower and you do not see them run their skateboards through a puddle. Because of this, skateboard bearing designers use a single lip seal on their rubber seals and use oil instead of grease. As a result, most skateboard bearing manufacturers recommend that you remove the seals on your bearings and reapply oil ONCE A MONTH. We are only aware of a handful of wheelchair users that maintain their bearings once per month.
But wait, skateboard bearings spin fast when they clearly have no oil. So doesn't that make them faster? And you are right, with no load, the bearing will spin very fast. The problem is when you get into your wheelchair and start pushing. A bearing with no lubricant will require a lot more energy to push than one with even the worst kind of lubricant.
So if you are taking your skateboard bearings apart and adding oil regularly, then you are good. The problem we are trying to solve is how to get all of the advantages of skateboard bearings without all the work.
Our bearings have a number of advantages over skateboard bearings and even original equipment manufacturers’ bearings.
Let’s start with water management. The first step in water management is preventing water from getting in. Our bearings are double lip sealed. This is twice the seals of all manufacturer bearings and most skateboard bearings. Second, we want to prevent the lubricant from getting out. We use Mult-Temp SLR high-performance synthetic grease. This grease has some of the best water inhibitors on the market. The double lip seal and water inhibitors reduce leaching and washing out compared to a standard skateboard or manufacturer bearing that does not have either.
Let’s talk performance. There is no doubt that oil is faster than grease, particularly in a cold start. Most manufacturers use an electronic motor bearing with a Mobil grease that is designed to turn into an oil at the high RPMs found in perpetually running engines. Great, but this is not how a wheelchair functions. Mult-Temp SLR is a LOW RPM grease that turns into an oil at the low temperatures found in wheelchair use and then back to a grease quickly as it cools off to protect from leaching.
Why we think the spin test is not the right test for a wheelchair bearing.
There is no doubt that a cold spin test with a skateboard bearing will show much better results compared to one of our bearings. This, however, is not a good test in our opinion because there is no weight on the bearing. In real-world conditions where there is little to no maintenance and high levels of humidity, the bearing with the best seals and lubricant will be a much more efficient bearing for someone pushing a wheelchair. Our brand of bearing is designed to give you all the advantages of an oil bearing, but require less maintenance over the long run because the lubricant stays in.