(Not as simple as it seems)
Read well these
info before ordering new bearings.
Bearing replacement is not an easy operation as it may seem.
Here below you'll find the basics on how to manage properly a cartridge bearing.
If you simply pop in a set of new bearings chanches are that they get damaged right from the start.
Additionally the installation of any kind of Hybrid & Ceramic bearings requires a really good specific expertise.
If your hub was originally equipped with standard bearings it will probably require micro-tolerance adjustments to axle and bearing fittings,
this to allow proper bearing rotation and durability (but these operations are for real experts only).
Alternatively send your hub to us for a proper servicing.
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a Worn-out Bearing
In most cases, when you have to extract a hub bearing, you can only push it out from its internal race.
This operation will generally damage or compromise the bearing races, however, if you are going to replace a worn-out bearing with a new one, this is a marginal problem.
Removing a Bearing that's Still Good
In case you wish to re-install a previously-used bearing you'll need to extract it in a safer way. Avoid hitting the internal race with a mallet at all. Even a threaded extractor or a bench-press can damage the bearing races.
Try to warm up the hub-shell with a hairdryer to facilitate an easier extraction of the bearing. The heat expands the alloy hubshell more than the bearing steel allowing to gently push it out by hand pressure and will also soften
Loctite (or other coaxial glue) that could have been eventually applied at the factory original assembling.
Inserting a New Bearing
A new bearing should always be inserted by pressing it on the same race that's going to be pressed into the hub fitting.
Cartridge bearings are generally fitted into the hub-shell with some interference on the outer bearing race, these cases apply pressure on the bearing external race only.
Note that the pressure should be applied exclusively onto the outer race, do not push flat on both races. Pressure or hits on the bearing's internal race will permanently damage the balls and races of your new bearing.
To properly press in new bearings are normally used specific insertion tools (each bearing size needs its specific insertion tool). Use only an inserting tool that is made for your exact bearing size.
Extralite offers a complete tool-set for hub maintenance: the Pro-tool kit 1 includes bearing inserting tools in every bearing sizes used on UltraHubs / HyperHubs.
Using an Old Bearing to Protect the New One
tAs a last resort, in absence of proper inserting tools, you could use the old bearing to carefully press in the new one as follows (use this method for emergency only)
- the 2 bearings should be perfectly aligned
- the mallet should hit only the external race of the worn bearing
- tap the bearing down in small increments and periodically make sure it's getting in perfectly flat.
- make sure the cartridge has reached it's final position contacting the bore end-shoulder, than do not over press.
As your new bearings are finally in their correct position rmemind that the hub axle has to slide into the bearings with only a mild pressure (the pressure amount is directly related to the bearing side-load capacity).
Forcing the axle through the bearings can again permanently damage balls and races of the new bearings.
Hub-Shell / Cartridge Bearing Interference Criteria
As general rule the pressing interference between hub-shell and bearing should be around 0.01mm. An interference of 0.02mm applied on a thin bearing (ex. 6802 - 6803 etc.) can compromise the ball-races tolerance.
On high quality bearings the matching/coupling of the parts leaves less than 0.003mm of play between races and balls before the installation.
If the races get pressed by a excessive pressure of the fitting bore or by the axle the balls will rub against their races and won't rotate smoothly and this brings to premature wear too.
The opposite case of a slightly loose bearing fitting can generally be properly dealt using Loxeal 83.21 / Loctite 260 or equivalent ?coaxial coupling' products and the then tuning well the bearing-preload (if you hub has it).
Hybrid Ceramic Bearings
The installation of Hybrid ceramic bearings is rather difficult and requires a very good specific expertise.
A proper bearing and axle insertion is even more critical when you are planning to mount hybrid-ceramic bearings. The ceramic balls feature a very hard surface that can ding the bearing steel races very easily. Additionally hybrid-ceramic bearings require a more precise tolerance match. Too much interference of the bearing outer-race with its hub shell fitting can often result in a rough-rolling bearing.The same thing can happen when the axle requires too much pressure to be slid into the bearing's inner-race.
Note: If your hub was originally equipped with standard bearings axle and bearing fittings will probably require micro adjustments of their fitting tolerances to allow proper bearing rotation and durability (these operations are for real experts only). Alternatively send your hub to us for this servicing.
Seals and Friction
Bearing seals are often the first resposable of bearing durability.
Tighter seals increase friction however do not over-estimate the effect. Actual bearing friction can't be judged statically by just rotating the axle with your fingers.
In the real use when the bearing balls rotate under load, they rub and rotate between races, which makes for much greater friction than a properly-fitted protective seal that could keep your bearings spinning smoothly for long time.
Good seals are really a must for MTB use.
Bearing durability is related to a great number of factors such as seal type and conditions, use mode and frequency, environment, washing mode and frequency, hub maintenance and lubing and more, this makes each individual case quit different.
In highly corrosive environments the ceramic ball resists to corrosion and help to clean the hard steel races. In such circumstances the overall durability could be even higher than steel bearings but this is generally uncommon.
Bearing friction should be judged under load when the balls rub and rotate between races. In these circumsances the use of hybrid ceramic bearings can offer an advantage.
Today’s Quality Standards
Hi-end bearing manufacturers have now acheived much higher quality standards than only few years ago. Quality hybrid ceramic bearings are now made with incredibly hard steel races that can survive the coupling with ceramic balls for a much longer life.
The latest generations of hybrid-ceramic bearings, such as ABI Zero and HDC, offer durability comparable to a steel unit. Earlier generations of bearings could only offer a fraction of the durability of a regular steel bearing.
In highly corrosive environments the ceramic ball resists corrosion and helps to clean the hard steel races. In such circumstances the overall durability could be even higher than steel bearings, however this is generally an uncommon situation.
Advantages and Disadvantages
Do not over-estimate the advantages of hybrid ceramic bearings. Their durability is equal or lower than steel ones, price is higher,all to gain a slightly lower rolling resistance.
When you are choosing to use hybrid-ceramic bearings be aware that the lower rolling resistance is the sole advantage they can offer besides a very very slight weight reduction (ca 1gr. less on each hub bearing).
Beware of Cheap Gimmicks
To enhance the feel of low-rolling resistance some non-serious manufacturer equip their bearings with non-contact seals and you can see them spinning for minutes- to your amazement.
Those bearings in reality last only few rides, as they collect dirt directly into their ball races and shortly thereafter require replacement (no surprise).
Among bike enthusiasts have tried to employ full-ceramic bearings in order to save weight and further reduce rolling resistance. Unfortunately with today's technology a properly dimensioned steel bearing cannot be replaced with a full-ceramic bearing of the same dimensions. Size should increase commensurately when moving from steel to ceramic and this nullifies any weight savings and requires a specifically designed hub-shell.
Additional note: even full-ceramic bearing manufacturers are openly not recommending their products for bicycle applications due to the ceramic material's fragility. Typical bicycle applications involve high impact resistance at low rpm (10-100 rpm) while the typical full-ceramic bearing application is at very high rpm (over 20,000 rpm) and absorbs only low impacts.
Load ratings of ceramics bearings
Ceramic has a modulus of elasticity higher than that of high carbon chrome bearing steel.
In the ceramic bearing, therefore, less deformation on the rolling elements (balls or rollers) generates higher stress at the contact point between the rolling element and raceway, when compared to a steel bearing.
Therefore, the contact stress between rolling elements and races of ceramic bearing would be significantly higher than that of steel bearing, under the same amount of load.
ca. 80% of steel bearing
ca. 70% of steel bearing
ca. 80% of steel bearing
ca. 20% of steel bearing
Load ratings of ceramic bearings compared to steel bearings.
The load capacity of ceramic bearings is accordingly decreasing when working temperature is increasing. HSC suggests choosing a larger load rating capacity bearing when using a full ceramic bearing for your application. Due to the brittleness of ceramics, full ceramic bearings are not capable of withstanding too much impact load. The outer races or inner races will generate cracks or even suddenly break under a certain amount of impact load.