I’ve been thinking a lot about bearings lately. Night and day. It keeps me awake
at night. Bearings are rolling around my brain. They’re damn tricky things. They’re
like hummingbirds; when everything goes right, they perform amazing feats. When things
go wrong, their life spans are measured in minutes and seconds.
When I say I’m thinking about bearings, I’m not just talking about the little rolly
metal bits. Bearings need seals to function properly in a harsh, off road environment
(despite what some overly optimistic suspension component manufacturers seem to think
these days). Grit, water, and small, hapless, furry animals can get sucked into the
whirring pieces. When this happens, the foreign objects will wreak havoc with the
tolerances and surfaces that bearings depend on to run right. Bearings have to be
protected from the hostile world we live in or they turn to expensive, rusty dust
in a hurry. Believe it or not, and I’ll bet you’ll be surprised to hear this burbling
from my mouth, sealing a bearing effectively is a damn tricky thing to do.
What about “sealed” bearings you ask? Everybody that has read a bike mag
(like they used to say in elementary school and now say in college – for comprehension
– not just looking at the pictures) has heard of sealed bearings. There are bike
parts that use sealed bearings, and these generally get bonus points in the magazine
reviews. They always cost more as well. The bearings have these spiffy little rubber
seals in them and a bike equipped with these little devils seems like it could be
ridden hard through an entire California winter without a failure.* And the spendy
hubs and bottom brackets that incorporate (a word I use with care these days) these
parts generally feel smooth as silk when you lift them cautiously (with permission
from the shop owner of course) from the dealer’s jewelry case and caress them longingly.
“Quality” everyone utters reverently… spinning an axle just for the rush.
“Quality” everyone in the area echoes obediently, trying to share the spiritual
moment. This must be the real deal right?
I don’t think so.
Language is a tricky thing, much trickier than bearings (see for a terribly tedious
example, Bertrand Russell, symbolic logic and all that junk). I feel like I can get
this bearings techno thing down well enough with a few months of dedicated agonizing,
but look at how badly I mangle the language you and I depend on when I spew my own
whacked dialect of Cal speak out for you poor folks to decipher, even after months
of practice (just look at the last sentence for proof!). Along those lines, the concept
of quality is hideously abused in the previous paragraph, though this is not an uncommon
use of the word. I’ll have to leave this for a subsequent rant or I’ll chew through
my word allotment much too quickly. (Pro pays me by the word, and they are reluctant
to give me a raise now that I’m actually getting paid to do what I do for a living.)
For now I’ll just have to follow up on the way seals (don’t) work, in spite of their
misleading name.
The theoretical notion of a sealed bearing is understandable. The name of the things
begs the question of course, as is often the case in double speak, but we moderns
have to overlook that sort of jive right? Is a sealed bearing really sealed, or is
it simply a bearing that happens to be equipped with little rubber thingies that
are called seals and might, in the best case, keep the junk out of the bearing’s
guts. And, in what conditions will the sealing system fail and let the muck pour
into those polished rolling jewels. Is “sealed” a scam or is it just a
poorly understood engineering principle that the hardworking but technically brain
dead marketing folks abuse regularly?
The seals that come on bearings work when everything’s right; there’s no question
about it. The suits that spend their productive lives deciding on the shape of the
sealing lips, the preload on said lips (I’ll leave it to your imagination to sort
out what a preloaded lip is – go ahead – be creative), and what the ideal seal material
might be are not fools. They have expensive college loans to pay off, and they’re
motivated. And they’ll butcher me if they think I’m giving them heard time!!! There
are definitely circumstances where these bearings are sealed up tighter than… well…
damned tight. But there are some situations where they leak like they’ve been hangin’
at the pub too long. No way around it.
Here’s the engineering bit. Had to get to it eventually, right? It’s a job. The sealing
lip has to touch the bearing’s inner race for it to work. Always. Non-negotiable
condition. If there is ever clearance between the two, the environment, the thing
all us greenies are scrapping to protect, goes right in and trashes everything. Preload
is, roughly speaking, the distance that the inner race of the bearing can move away
from the seal’s static position before it loses contact; the hero in this case.
Push hard on those cranks or jump a bit too high and the seal and journal lose contact.
Slam a berm a bit off angle and the axle flexes a lot. Shit goes in. You lose. No
way around it. The hot shot bearing designers didn’t think about MTB hammers putting
large amplitude, low frequency load onto their pet projects. If they did, the thought
came as a nightmare. There are no standard bearings that fit this application. Don’t
let the hypemeisters tell you otherwise.
* I should explain that last statement. After the great Dorking “mud” fest
Chipps organized at Bike 95 last year, an epic event where we poor Yanks were supposed
to flounder around in deep English glop for the photographer all day, at our expense
of course, flopping over and looking like fools, and a good idea if nature would
have been cooperative, but where the only mud I saw was where Jo Burt took a very,
very long leak on the side of the trail, longer than any normal human ought to, and
I certainly didn’t ride anywhere near that awesome puddle, seals or otherwise, I
figure our sunny California winters are really much more extreme than yours. There…
I said it. I realize that it may be a controversial opinion, but I’m a scientist,
and there’s nothing more persuasive than direct experience, Jo Burt’s feat not withstanding.
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