Open vs sealed bearings: how much speed do seals actually cost?
2026-09-15
Using our own parameter-table data to explain how seal type affects the grease-lubricated limiting speed, and how to read that number when specifying.
The question comes up on almost every enquiry: does adding a seal cost you speed on the same bore size? The honest answer is not yes or no — it depends on which seal and on which number you compare against.
Two terms worth separating
- Limiting speed — the figure in our parameter table. It is the maximum speed permitted under that lubrication method under stated conditions. It is a thermal and friction limit, not a guarantee that any speed below it is safe in your application.
- Operating speed — the speed your equipment actually runs at. When specifying, your operating speed should stay below the limiting speed with margin.
In short: the tabulated limiting speed is a screening threshold, not a licence for your machine speed.
How the four seal families differ
Our table covers seven variants: open, Z, ZZ, RZ, 2RZ, RS and 2RS. By their limiting-speed behaviour they fall into three families:
| Family | Variants | Construction | Limiting speed in our table |
|---|---|---|---|
| Unshielded | open | both sides open | highest for that model |
| Metal shields | Z / ZZ | one / both sides shielded | same as open |
| Rubber seals (light-contact) | RZ / 2RZ | one / both sides, NBR rings | same as open |
| Rubber seals (contact) | RS / 2RS | one / both sides, NBR rings | lower than open (measured range below) |
Two conclusions follow:
- Metal shields (Z / ZZ) do not reduce the grease-lubricated limiting speed in our table — it matches the open version.
- Light-contact RZ / 2RZ also match the open version in our table (note: although they carry rubber rings, our data does not show a reduction).
- Contact-type RS / 2RS do reduce it. That is the cost of the added friction.
"How much lower" cannot be generalised
This is where it is easy to go wrong. The reduction differs from model to model — but the spread is narrower than often assumed. Recalculated against our 100 base models:
- across the 74 base models where the figures are comparable, the ratio of the RS (or 2RS) grease rating to the open rating falls between 53.6% and 80%;
- that is, the highest is about 1.5× the lowest — not several times;
- for the remaining 26 models the sealed variants do not list the figure. In our usage, "not listed" does not mean "unsupported" — please ask us.
So:
- ❌ Do not apply a single percentage (for example "sealed is 60% of open") — for a specific model that is often simply wrong.
- ✅ Do open that model's own page and compare its open and sealed figures side by side.
This is also why we built the bearing selector: it screens on each model's own listed speeds rather than substituting a catalogue-level average.
Using the number when you specify
- Establish your operating speed, and keep margin.
- Check the lubrication method: grease and oil have different limiting speeds, listed separately.
- If your speed approaches the limit for the model you picked, our engineers must confirm the selection before you commit — the permissible speed also depends on load, temperature rise, lubricant type and maintenance conditions.
All figures here come from our factory parameter table. Where a rating is not listed for a variant, the sample did not provide it — that does not mean it is unsupported. Please ask us.
Want us to screen it for you?
Send us the shaft diameter, available envelope, operating speed and environment — or use the bearing selector, which screens on each model's own listed speeds rather than a catalogue-level average — and we will shortlist models and confirm the final selection.