This post compares the advantages and disadvantages of DU bearings and standard ball bearings.
What are DU bearings?
DU bearings/bushings are a hollow cylinder (sleeve) that rotates around an axle. They are made of metal polymers and have PTFE (Teflon) coating acting as permanent lubrication.
Note: “DU” stands for “Dry Unlubricated” because DU bushing/bearings have their own lubrication (Teflon impregnation.)
What Are Ball Bearings?
Ball bearings rely on steel balls to separate two rotating elements (races). The function of the bearings is to reduce rotational friction and support radial and axial loads.
The Advantages of DU Bearings/Bushings
DU bearings have fewer moving parts and are therefore less likely to malfunction. The simpler the unit, the more reliable it is.
DU bearings can take more stress/abuse than ball bearings of the same size. Hence why DU bearings/bushings are found even on some expensive bike pedals.
- Dirt Tolerant
DU bearings can tolerate dirt better than unsealed ball bearings. This makes them even more wear-resistant.
The simplicity of DU bearings makes them lighter too. That said, the weight savings are inconsequential, especially when the scale is small.
The Disadvantages of DU Bearings/Bushings
The main disadvantage of DU bearings is that they’re disposable. Once the sleeve is worn it develops play and the only way to eliminate the issue is a replacement. That said, in most cases, it makes more economic sense to replace the entire unit if it’s cheap.
For example, it makes little financial logic to replace the DU bushings of a 15-dollar pedal.
DU bearings/bushings experience more friction than ball bearings and do not rotate as smoothly.
The Advantages of Ball Bearings
- Smoother Rotation
Ball bearings offer smoother rotation because they overcome friction by rolling whereas DU bearings rely on sliding.
If the ball bearings aren’t sealed, they can be serviced. Servicing can prolong their time substantially. For example, if a pedal starts to complain, it can be disassembled, cleaned and re-lubricated. If there are damaged ball bearings in it, they can be replaced.
Since it’s fairly easy to access the ball bearings of a non-sealed bearing, this procedure isn’t deprived of financial logic. That said, when the races of the bearings start to go bad, the entire unit has to be replaced.
Note: If the bearings are sealed, they’re not meant to be serviced. Instead, the user is expected to replace them when a problem occurs.
- Better Suited For High-speed Operations
When a unit (e.g., a wheel) is operating in a high-velocity environment, a bearing works better. Hence why bicycle hubs always have ball bearings.
Bushings, on the other hand, are more suitable for slower rotations and heavy loads. Hence why you see them often in bicycle pedals. (Pedals do not have to rotate nearly as intensely as a wheel.)
The Disadvantages of Ball Bearings
- Prone To Contaminations
If the ball bearings aren’t sealed, dirt and moisture can get into them. Hence why unsealed ball bearings need more frequent servicing. Conversely, DU bearings are not as affected by contaminations.
- Difficult to Manufacture Accurately
Ball bearings can be acquired for cheap, but the low-end units usually aren’t built accurately enough to spread the load evenly. Hence why in some cases, a couple of low-quality ball bearings may cost less than a DU bushing.
- Weaker for The Same Size
DU bearings offer more strength for the same size when compared to ball bearings. This is a strong incentive to use them in small components such as pedals.
A quality bearing built within tight tolerances can cost five times more than a DU bushing.
Summary: What You Need To Know
- DU bearings/bushings represent a cylinder rotating around a shaft/axle. The inside of the cylinder is impregnated with lubricating compounds.
- Ball bearings rely on steel balls to separate two rotating elements (races). The function of the bearings is to reduce rotational friction and support radial and axial loads.
- Quality ball bearings offer superior rotation because friction is overcome via rolling.
- The high cost of quality bearings and the difficult manufacturing process act as a strong incentive to use DU bushings when the application permits it. In the case of bicycles, DU bushings are usually found on the pedals.
- DU bearings offer more rigidity and strength than bearings of the same size. (Hence why it makes even more sense to use bushings on bike pedals.)