On a 60 mm shaft the seal is a rounding error. On an 8 mm shaft it can be most of the friction. A standard 2RS lip on a 608-size bearing adds enough drag to change the starting current of a small motor, flatten a battery-powered device and show up as heat in a sealed instrument. Low-torque sealing is a separate design problem with its own answers.
Running torque of a lip seal is roughly constant with speed, but starting torque is higher: the lip has to break static contact and the grease has to be sheared from rest. In a gearmotor that has to start under load, or a device that wakes up hundreds of times a day, starting torque dominates the design. That is why non-contact seals are standard in battery tools, camera gimbals and dosing pumps.
Below about 15 mm bore, the seal is a significant fraction of total friction and the upgrade to a non-contact design pays for itself in efficiency. Above 40 mm bore the same change saves a smaller percentage but also reduces heat, which matters more than torque in continuous duty.
| Contact 2RS lip | 100% — the reference drag |
|---|---|
| Non-contact 2RZ / VV / LLB | 25–35% of contact-seal drag |
| Steel shield 2Z | 10–15% of contact-seal drag |
| Open | Baseline, rolling resistance only |
| Starting torque | Disproportionately affected — the lip must break static friction |
| Effect on small motors | Measurable change in no-load current and temperature rise |
| Seal thickness | Thin-section lips exist for instrument bearings |
| Trade-off | Lower drag means weaker protection against fine dust |
| Type | Running drag | Starting drag | Dust | Water | Speed |
|---|---|---|---|---|---|
| Contact seal (2RS) | 100% | 100% | Tight | Splash | 60–70% |
| Reinforced contact (RSH) | 105–115% | 110% | Tight | Splash | 60–70% |
| Non-contact seal (2RZ) | 25–35% | 30–40% | Good | Light | 80–90% |
| Steel shield (2Z) | 10–15% | 10–15% | Coarse | No | 85–95% |
| Open | 0 (reference) | 0 | None | No | 100% |
Rubber contact seal on both sides — maximum protection
Read →Steel shield on both sides — high speed, coarse dust only
Read →Non-contact rubber seal — shield friction, better sealing
Read →No seal — maximum speed, relubrication access
Read →The brand crosswalk for contact rubber seals
Read →SKF's reinforced contact seal for larger bores
Read →Open has the lowest, then a steel shield, then a non-contact rubber seal, then a contact lip seal. If the housing cannot be sealed, a non-contact seal is the practical minimum.
Yes. On small bore sizes the lip friction is a meaningful share of total losses and it raises the no-load current. In battery-powered devices that shows up directly as runtime.
Usually yes. Indoors, with no water and only coarse dust, a 2Z shield gives most of the protection at a fraction of the drag.
No — non-contact seals have no rubbing surface, so they do not wear. Their weakness is protection, not life.
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