July 4, 2011
FLO Cycling - Components Series Part 1 - EZO Bearings
Today we are starting a components series. High quality components are important to us and they are one of our three key design criteria. The other two are great aerodynamics and affordable prices.
We feel it is important to explain what we mean by "high quality". We are explaining our bearings by going through the specs. These are the things we worry about so you don't have to. Still it is nice to have access to this data when making a buying decision that's right for you.
You can see more of our component series in the links below.
You can see more of our component series in the links below.
FLO Cycling - Component Series Part 2 - FLO VORTEX HubsFLO Cycling - Component Series Part 3 - Sapim Spokes
FLO Cycling - Component Series Part 4 - FLO WIDE RIDE Rims
FLO Cycling - Component Series Part 5 - Ceramic Bearings
Bearings are located inside the hub of a wheel. They allow the hub to spin freely. Bearings come in all shapes and sizes but most of them have the same basic components. There is an inner ring, an outer ring, ball bearings, and a bearing spacer. Here is a picture of a bearing where the ball bearings are visible.
The components are easily identified with the exception of the bearing spacers. In the picture above the bearing spacers are the black pieces between the ball bearings.
Here is a picture of a partly disassembled FLO VORTEX hub. You can see the bearing in the picture. Note the ball bearings are not visible since they are covered with a piece of rubber which has Japan written on it. You can see the inner and outer rings have a silver color.
|Bearing in our Flo Vortex Hub|
Japanese EZO Bearings
We have made mention several times that we use Japanese EZO Bearings. What does that mean? The company name is EZO and they manufacture their bearings in Japan. They are arguably one of the best bearing manufacturers around. Here is a quote regarding EZO bearings.
EZO are a Japanese company and a specialist manufacturer of high precision bearings for over 30 years and have a deserved worldwide reputation amongst customers and bearing manufacturers alike for total consistency and reliability. EZO have factories in Japan and China and their bearings are used the world over in precison instruments, automotive applications, electric motors, top-of-the-range audio equipment, robotics.. in fact anywhere where quality cannot be compromised.
The easiest "non-scientific" way to test a bearing is to test how it feels. When we were selecting bearings for our hubs we quickly learned that some bearings just felt better and spun more freely than others. After looking into the difference, we discovered that EZO bearings were what made the difference.
We didn't just want to leave it to a feel. We wanted to ensure the bearings were capable of handling the loads required and that they would have a long life. This is where the spec sheets came in handy.
EZO 6900RU and EZO 6902RU
Our hubs use two different bearings. The front hubs use 2 EZO 6900RU bearings and our rear hubs use 4 EZO 6902RU bearings. Take a look at the pictures of the EZO 6902RU below. You can see the markings on the rubber seal.
|Japan and EZO Marking|
I am posting the spec data for the two bearings that I will use as the post continues.
First let's talk about the two diameters. The bore diameter is the inside diameter and the outer diameter is obviously the outer diameter. We checked the precision of the bearings with a digital caliper and were amazed to see how tight the tolerances were.
|Bore Diameter Measurement|
|Outer Diameter Measurement|
The width is the thickness of the bearing and was equally accurate. The accuracy peaked my interest so I went out to EZO's website and found the following picture, which I though was pretty cool. It shows two micro bearings on a US dime. If they can handle this type of accuracy our relatively huge bearings are no problem.
|Two EZO Micro Bearings on a US Dime|
Cr and Cor
Next up is the Cr and the Cor. These are symbols for "Basic Dynamic Load Rating" and "Basic Static Radial Load" respectively. Yeah, it didn't really clear it up for me either. Basically, the dynamic load rating is a measurement that relates to a load and 1,000,000 revolutions. The bearing is tested to determine the maximum load where the bearing will remain operable for 1,000,000 revolutions. The static load rating is a measurement of how much weight can be applied to the bearing before the bearing starts to deform.
This could be either the ball bearings loosing shape or the rings developing grooves.
So how does this relate to our wheels and what are the important things to look for? First of all 1,000,000 revolutions on a standard 700c wheel with a 23mm tire is roughly 1,300 miles. This is not very far for a set of wheels. Understand that the rating is for the maximum load and this changes as the load gets lighter. To show the maximum loads allowable I created a table that shows the maximums in units that make more sense to most of us then Newtons. I used both kilograms force (kgf) and pounds force (lbsf). This is essentially the same thing as kilograms and pounds. Don't let the "f" confuse you.
|Cr and Cro Values in kgf and lbsf|
We can see here that a single front bearing can withstand 285 lbs before it deforms and a rear bearing can withstand 506 lbs. We also see that the front and rear bearings can withstand 604 lbs and 969 lbs respectively for 1,000,000 revolutions. This basically states that even thought the load is over the static load rating it will still remain operable. It seems a bit odd, but under static load the bearings do not have time to recover from the applied load. It's this constant state of deformation that lowers the static load rating when compared to the dynamic load rating. Even though these limits exist, it is still good practice to design a system that is far away form these limits. I created a sample case with 72.72 kg or 160 lbs rider to show the actual force applied to each bearings. Remember there are two bearings in the front hub and 4 in the rear hub. This means the weight is evenly distributed over these sets of bearings. I made the assumption in my calculation that the weight distribution of the rider is 45% over the front wheel and 55% over the rear wheel. I am sure there are lots of arguments against this but it's purely for explanation purposes. Let's be honest, in the real world the load is constantly shifting anyway. The table below shows the load applied to each bearing.
|Bearing Loads with a 72.72 kg or 160 lbs Rider|
We can see that our bearings can handle at least 8 times the actual load applied with the rider in the example above. This is exactly what we want to see. You want a large safety factor so you can maximize the life of your bearings and prevent damage. Unless you use our wheels for a weekend big air competition, you can rest assured the bearings can handle your weight.
The maximum speed column is an interesting one. It basically means how fast can the bearing spin and still be operable. The symbol "rpm" stand for revolutions per minute. This means how many times the bearing makes a complete turn in one minute. Again, I wanted to use a term that is more common. I converted the rpm value to miles per hour (mph). I assumed the wheel had a circumference of 2,100 mm and used the following equation.
mph = rpm * 60 * 2,100 * 0.00000062137
The 0.00000062137 is the conversion from mm to miles. Check out the values below. I had to laugh when I saw them.
|Max Rider Speed on mph|
The speed of sound is 761.20 mph. The means you would have to break the sound barrier by a factor 3.50 for the EZO 6900RU or 2.67 for the EZO 6902RU before you would run into any problems. If you can ride your bike that fast, we are guessing something else will fail first :). Needless to say our bearings have you covered when it comes to max speed.
The cage type is the type of spacer used for the ball bearings. A steel ribbon looks similar to an egg carton. There are two pieces that come together to enclose the ball bearings. It's a good design coupled with the grease. It helps keep debris from coming in contact with the ball bearings and ultimately the rolling surfaces. The grease traps any potential debris if it gets past the seal. I took off the rubber seal to show you what the inside looks like.
|Steel Ribbon Cage|
The ball bearing section is pretty self explanatory. When referring to the "Bearing Spec" table above, the first column is the number of ball bearings per bearing and the second column is the size of each bearing. The number and size both relate to the rest of the data. The calculations that go into the rest of the data are far beyond this post. Regardless, you can rest assured they are optimized for these bearings.
Finally we have the seal. This is the rubber piece that had the 6902RU and Japan EZO markings. For a bicycle the seal is important. It keeps out dirt and debris to help maximize bearing life. The 2RU means the seal is a non-contact seal. This means it does not make contact with the ball bearings. This is important because it reduces the amount of friction. The less friction, the less resistance, which is exactly what we want. I took a couple pictures to show what it looks like by itself.
|Outside Surface of 2RU Rubber Seal|
|Inside Surface of 2RU Rubber Seal|
I hope that this post helps you begin to understand what FLO Cycling means by "high quality" and that it increases understanding of bearings. We feel each piece is important and have paid special attention to each one. The selection process has been very important to us so we can deliver a wheel that meets our design goals and hopefully yours too.
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