Open vs sealed bearings: how much speed do seals actually cost?

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 four families:

Three conclusions follow:

1. Metal shields (Z / ZZ) do not reduce the grease-lubricated limiting speed in our table — it matches the open version.
2. 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).
3. Contact-type RS / 2RS do reduce it. That is the cost of the added friction.

For what each suffix stands for — and which fields stay identical when you switch suffix — see bearing suffix codes.

"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.

To see the difference on a specific model, open 6205 or 6305: the model page lists the open and each sealed variant side by side, which beats any generalisation.

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

1. Establish your operating speed, and keep margin.
2. Check the lubrication method: grease and oil have different limiting speeds, listed separately.
3. 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.