What
makes a good skate bearing?
Abec rating? Lubrication? Seals? Cage/retainer? The answer
is all of these. The problem is that some retailers will throw a
lot of jargon at you to convince you that their bearings are superior.
You have to decide what is relevant but, not being a bearing expert,
how are you supposed to know? As experts, we will try to explain
in plain simple language in the hope that you will go away with
a better understanding of what to look for. For more details see
our technical
pages.
Material:
Rings: SAE52100 chrome steel is the most commonly used steel
for bearings because it is hard wearing. It will corrode so if
you skate in the wet, clean the bearings after use to avoid rust
(see the section on cleaning below). Stainless steel is slightly
softer but will still last a long time as, even if you are very
heavy, the bearings are designed to take much greater loads than
you. We do offer stainless steel as an option for those who like
the rain. See Technical
Data - Bearing Material).
Balls: Chrome and stainless steel balls will take high loads and
speeds and are absolutely fine for skaters. Silicon nitride (ceramic)
balls are much lighter than steel balls and about twice as hard.
These factors reduce running temperature and minimise wear meaning
longer bearing life. The extra
hardness of ceramic balls means they are less likely to be damaged
if debris gets into the bearing. If used with a small amount of
low torque grease, bearing life can be significantly extended. These
hybrid bearings (bearings with ceramic balls) are capable of higher
speeds too but higher speeds are not necessary for skate use. As
they are lighter and generate less friction, they require less effort
to accelerate and maintain speed. However, this will not be a noticeable
difference compared with, for example, using a stiff grease in your
bearings.
See more details on hybrid bearings at the Cerbec
website.
ISO/Abec rating (tolerances/precision grade)
ISO ratings are expressed in millimetres whereas Abec tolerances
are measured in inches (see Technical
Data - Tolerances). These standards control the dimensions of
the bearing such as internal and external diameters and width. For
example, the inner ring diameter (bore size) of a 608 bearinng is
8mm. If the bearing is P0 (Abec1), the inner diameter can be no
bigger than 8mm but it can as small as 7.992mm. The smallest for
P6 (Abec3) is 7.993mm, for P5 (Abec5) its 7.995mm and for P4 (Abec7)
its 7.996mm. The ISO/Abec rating also controls the roundness of
the bearing by limiting the amount of variation allowed on each
inner or outer ring. The ISO/Abec rating DOES NOT control the looseness
of the bearing. That is down to "Clearance" (see below).To
be honest, ISO/Abec ratings are way over-hyped in the skate world.
The difference in inner ring tolerance
between P0 (Abec1) and P4 (Abec7) is a matter of 4 microns or 0.004mm
and none of the other components on the skate/skateboard would be
made to such a standard. There are a lot of much higher precison
applications in industry where P5 or P4 bearings would not be considered
necessary. As for Abec9, there very few manufacturers in the world
capable of making genuine Abec9 bearings and they are very, very
expensive! An improvement in smoothness can be achieved by selecting
a low noise bearing (see "Noise Rating"
below). However, many skaters seem convinced that the ISO/Abec rating
gives a certain peace of mind so our skate bearings are genuine
P5. There are factories out there who will stamp Abec1 bearings
with "Abec5" and others who make bearings with high tolerances
on the inner and outer diameters but won't worry about smoothness
of the raceways (grooves inside the inner and outer rings that the
balls run in) or the roundness of the rings so making the whole
thing a waste of time (and your money).
Speed
A standard bearing is rated up to a certain
speed (according to the size). This can be increased by use of a
high speed cage, a high speed lubricant, ceramic balls or, very
slightly, by a higher precision grade. None of this is relevant
here as you will never even
approach the maximum speed of a standard bearing!!
As an extreme skater, you may occasionally approach 2500 to 3000
rpm whereas the bearing will manage well over 30,000 rpm with a
standard cage and over 60,000 rpm with a high speed cage. Much more
relevant is torque or drag (see below).
Torque and drag
Bearing torque relates to the amount of force required to
rotate a bearing from rest (starting torque) and to keep it running
(running torque). With skate bearings, this turning force is your
weight acting on the skate causing it to roll downhill or you pushing
off on your board to accelerate. Starting and running torque figures
for a bearing are influenced by a number of factors such as raceway
roundness and smoothness; seals; lubricant and cage. In plain language,
a bearing with a very stiff grease and tight seals will be harder
to turn and will not allow your skates to roll freely. Also, a cheap
bearing will not actually spin as freely because it is not as round
although you would need a bearing torque tester as the difference
is too slight to feel by hand.
Quite simply, the less drag you have on the bearing,
the faster you can accelerate and the longer you can freewheel but
the difference in drag between our low torque grease and a light
oil is not noticeable unless the turning force is really small.
Skate bearings do not need to be
oiled to run freely with you onboard. You may notice the
difference when you spin the bearing with your finger but not when
you're actually skating (there are a few grammes/cm difference in
frictional torque).
The difference is even less once the bearing has been running for
a short time as the grease warms up and gets softer. Light oils
are used for bearings in sensitive instruments where the force acting
on the bearing is likely to be very small. If you really insist
that your bearings spin freely, use light oil or nothing at all
in the ceramic ball type. They will just wear out faster than the
greased type.
Cage/retainer
A good all purpose steel cage is fine for
skate bearings. We use a high speed nylon cage simply because, although
it does have better sliding characteristics and slightly better
low noise performance, it is more forgiving if the bearing is contaminated
with dirt or being used with inadequate lubrication which may be
important if your bearings are overdue for cleaning and relubrication.
The stainless bearings have a stainless steel cage.
Seals
Bearings can be supplied with metal shields to keep out the grit
or rubber seals (sometimes called contact seals) which will stop
dust too but seals have one drawback. They rub on the inner ring
of the bearing to create an effective seal so greatly increase bearing
drag which is not great for skate use. A better solution is the
non contact seal. This design
gives better protection than shields but without the drag caused
by normal seals. Finally, as they are only a push fit in the outer
ring of the bearing, non contact seals can be easily removed and
re-fitted when you clean and relubricate the bearing. IMPORTANT
- the 688 micro skate bearing has one seal. When the bearings are
fitted, the seal should always be on the outside of the wheel.
Noise Rating
Bearing rings and balls are not perfectly round and the balls
and raceways, even after extensive fine grinding and polishing,
are not perfectly smooth. These machining/grinding imperfections
cause extra vibration. Our skate bearings are EMQ grade which means
they had additional noise testing after production and only the
lower noise P5 bearings were selected. These have better roundness
and smoother raceways which means a smoother running bearing.
Clearance
The internal clearance of the bearing relates
to the space between the balls and the raceways. A bearing is designed
to take mainly radial load (vertical load on skate bearings) and
some axial (side) load. The clearance on our skate bearings is slightly
larger than standard and designed to allow the bearings to take
a greater side load when needed.
Lubrication
Correct lubrication is vital to keep the
inner surfaces of the bearing from getting too hot which causes
more rapid wear. The most effective lubrication for a sealed or
shielded bearing is grease. Oil is often used in bearings but normally
where rotation is very slow or where it possible to continuously
lubricate the bearing with, say, an oil jet or spray. Grease is
basically an oil mixed with a thickener to keep it in place. It
normally creates more drag than oil but only slightly more if the
grease is low torque (free-running) and the amount used is quite
small.
The lubricant in our chrome steel 608 type skate
bearings is manufactured by Klueber who make a range of high grade
lubricants for some of the most demanding applications in industry
and aerospace. "LDS18 Special A" is a high speed, low
torque grease. The grease in our stainless steel 608 type and our
688 type mini skate bearings is also a high speed, low torque grease
made by Kyodo Yushi of Japan. They both contain hard wearing lithium
which is more than tough enough for skate conditions. They possess
good water resistance, useful for skating in wet conditions. A standard
amount of grease for a ball bearing is about 30 percent of the internal
space of the bearing but we have reduced this to 20 percent. This
means minimal drag on the bearing while giving very effective lubrication.
We offer tubes of LDS18 grease for those who want to clean and relubricate
their own bearings. Remember, you can relubricate the ceramic type
with oil or nothing at all if that is your preference but the bearing
will wear out faster and the difference in performance will be minimal.
Learn more about Klueber at www.klueber.com
or Kyodo Yushi at www.kyodoyushi.co.jp/eng/
Packaging
Bearings are precision engineered components and secure packaging
is important to keep them from being damaged in transit and prevent
contamination. It should also be cost effective. You should pay
for the bearings, not the packaging so we do not supply our bearings
in fancy tins or supply free stickers.
Cleaning and Regreasing
Checking
for wear: Its not difficult
to to check your skate bearings for wear. Over a period of usage,
wear will cause flaking or spalling of the raceways and fine particles
of metal will break away. This causes
increased roughness in the bearing. At this point the wear will
accelerate as the metal debris scores and dents the balls and raceways.
This process is greatly speeded up by any dirt that has worked its
way into the bearing. If you hold the bearing's inner ring between
a thumb and finger and then turn the outer ring with your other
hand, you will be able to feel a roughness or grittiness if the
bearing is worn. OK, this may be due to dirt in the bearing so if
the roughness is still there after cleaning, the bearing is due
for replacement. Worn bearings often feel rougher after cleaning
because grease has a dampening effect.
Seal removal:
As mentioned in the section on seals, the non contact seal can be
easily removed with a thin blade such as a Stanley knife, a trimming
knife, a small screwdriver etc. CAREFULLY slide the tip of the blade
between the seal and the inner ring taking care not to damage the
seal. Push the tip just under the seal (but not too far as you don't
want to catch the bearing cage!!) then gently prise the seal out.
The outer lip of the seal sits in a groove in the outer ring of
the bearing.
Lubricant
removal: It is important to
clean the old grease (or oil) out as this may contain particles
of dirt or grit which have an abrasive effect on the ball and raceways.
The grease can be removed by soaking in a solvent such as white
spirit. Agitating or spinning the bearing in the solvent will help
speed up the process. You may need to dip the bearings and re-spin
a few times to remove all the old grease. The bearing will spin
freely if its clean. It will save you money if you filter the solvent
through a lint free cloth to remove larger dirt particles and grease
solids during the cleaning process rather than using fresh solvent
as soon as it gets dirty. You can spin the bearing to remove most
of the solvent and place on a clean surface to dry. If using a flammable
cleaner, make sure you keep well away from any flames or other possible
sources of ignition and UNDER NO CIRCUMSTANCES should you ever use
petrol/benzine/gas (depending on the country you live in) due to
the risk of fire or explosion. You
must always allow the solvent to fully dry off before re-lubricating
or the solvent will break down the lubricant.
You can use WD40 to clean the bearing but you should clean the bearing
in solvent before regreasing as the remaining film of WD40 will
stop the grease from properly adhering to the inner surfaces of
the bearing. Bearings can also be cleaned with a water-based degreaser
but they will need a final rinse in water to remove the degreaser.
Care must be taken to remove any remaining water quickly from chrome
steel bearings or they will rust. This can be done by immersing
in oil or spraying thoroughly with WD40. The problem here is that
you should then remove the oil or WD40 before greasing so adding
another process to the cleaning procedure.
Lubricant
application: Without
the right equipment, it is difficult to regrease with exactly the
right amount so guesswork is involved here. You want to fill roughly
20 percent of the internal space of the bearing with grease. It
is better to evenly distribute the grease so work round the bearing
squeezing a small amount between the balls. If you use too much
grease, don't worry. It will make the bearing slightly stiffer and
you can always carefully remove some of the excess. Once the greasing
is done, rotate the bearing several times by hand to spread the
grease around the raceways (these are the grooves or tracks inside
the inner and outer rings that the balls run in). If you choose
to use oil, a few drops will suffice but you should also spin the
bearing after oiling to distribute the oil evenly.
Seal replacement:
The rubber seals can be refitted by
pressing the outer lip of the seal into the narrow groove in the
outer ring of the bearing. This is a snap fit and is done by hand.
When you have replaced the seals, check that the bearing rotates
freely enough. If it feels much stiffer, the seals may not be correctly
fitted.
Protecting
your bearings: To protect against
corrosion, apply a light oil coating to outer surfaces of chrome
steel bearings (e.g. 3 in 1 or WD40).
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