Quick and Dirty
While riding a bicycle, there are a plethora of aspects that will affect overall speed and required effort. Some of these are: tire flex and pressure, frame flexing, chain friction, road bumps, road material, wind, rain, the dog you’re trying not to hit, and not to mention the cheeseburger and fries you ate last night. Microns of tolerance in a bearing will have a vastly smaller effect on the overall max RPM and rolling resistance than the above list or some good old-fashioned training. The main exception to this is a bike that is reasonably set up with components (bearings included) that are in reasonable condition. We know that this is a strong statement to some people. If you want to know the truth in the engineering, keep on reading. If you just want to spend the dollars on a good bearing to brag to your friends about, please click here. We fully understand and partake in making sure our bikes are braggable.
Difference Between ABEC Bearings
The difference from an ABEC 1 to an ABEC 7 bearing for radial runout is 7.5 microns for a 6000 (10mm ID) bearing. This means that if a skilled person with a dial gauge and a professional set up checks the bearing for roundness on the raceway itself, as they are spinning the bearing, the deviation of the radius from nominal for an ABEC 7 is 2.5 microns and an ABEC 1 is 10 microns. This is not measuring with a tape measure, Vernier caliper, or even the vast majority of micrometers. This is measuring with dial gauges that are frequently calibrated, a correct set up of most likely custom tools, a temperature-controlled room, and most importantly, someone who knows what they are doing. This takes training, practice, and time. Some expensive machines do exist to support this measuring. A good brand is Taylor Hobson if you want to look them up. Another important aspect that many people forget is that the bearing needs to be in a temperature and humidity-controlled room for hours (to homogenize the temperature). 52100 bearing steel has a coefficient of thermal expansion large enough to grow about 1 micron for every 10°C [18°F].
Microns and Ball Bearings
Let’s take a look at what 7.5 microns actually is…
Arguably, a human hair is 17-181 microns, a sheet of paper is about 100 microns thick, and an average red blood cell is 8 microns. The next time someone is telling you that they can feel the difference in their new bearing precision, ask them how their red blood cells are doing. Having said all of this, proper bearing grease, proper bearing grease fill, contact vs. non-contact seals, etc. will make a difference to the rolling friction of a bearing. This will feel like riding against a 20-mph vs 0-mph gust of wind. Note that this feeling is not the same as feeling the precision of the bearing. Feeling the precision of a bearing is like riding on a gravel road vs. a newly paved road (i.e. roughness vs. smoothness). This means that a proper set up ABEC 1 bearing could easily feel much better than a poorly setup ABEC 7 bearing on your bike.
Bearing Package Dimensions
Another aspect of precision is the package dimensions. The easiest way to look at this is inner dimension, outer dimension and width of the bearing. Using the same 6000 bearing size example, the below table outlines the different tolerances for the different precisions – again all in microns (micro meters). If there is a person who is trying to sell you a true ABEC 7 bearing, and they state it is tighter tolerance, this is true. BUTT (two T’s…), ask them, or at least ask yourself, what is the machining tolerance of my thru-axle and the hub that my bearing will go into? If you are able to install your bearing by hand with little effort, then an ABEC 7 bearing is not worth the money for package dimensions – repeat, for the package dimensions. Doing this by hand means that there are at least a few microns of gap, if not much more. If you have multiple microns of gap, what is the point in paying for a tighter tolerance when the bearing is going to orbit on the axle anyway? The flip side argument we are expecting to get is poor + great is better than poor + poor. We agree. But bring in cost to benefit, proper set up, and the list of other possible watt sucking potential influences above.
Higher precision bearings are very valuable to many people. But the point in writing this is that the average biker/hobbyist/charity rider does not need to pay hundreds of dollars for ABEC 7 bearings, let alone ABEC 5. Spend tens of dollars and take care of your ABEC 1’s and you will be happy. Taking care of your bearings will make a much larger impact than spending more on your bearings unless you are showing up your buddies’ bike, then by all means get the better bearings.