On 18 Apr 2006 10:07:35 -0700,
[email protected] wrote:
>Michael Press wrote:
>> > > > This makes me wonder about the conditions in which jeverett
>> > > > gets 18K from a chain. He suggests that it comes from lubing
>> > > > it only when it is clean, IIRC. But then he lives in Seattle.
>> > > > Perhaps it's because his chain is constantly washed clean by
>> > > > the rain.
>> > >
>> > > It does not work that way. Road spray is not water. It is
>> > > a slurry of water, sludge, and grit. Chains get dirtier in
>> > > the rain, not cleaner; and dirtier than in dry weather.
>> > > A full chain case is another matter.
>> >
>> > I disagree, but you'll note that I am hypothesizing, not stating as
>> > fact. You are stating as fact. You got anything whatsoever with which
>> > to back up your statement or are you just huffing and puffing?
>> >
>> > Also, I dunno where you live, but here in san jose, ca, we have a wet
>> > and a dry season. The first rain or two of the wet, I would agree
>> > with your statement. After that, the roads are squeaky clean for the
>> > following six months.
>>
>> Look at any car that has traveled wet roads around here
>> (San Francisco Bay area). The lower body panels are thick
>> with grit. Look at the bottom bracket a bicycle that has
>> traveled a wet road. Road spray all along the seat tube,
>> and when it dries: grit.
>
>Okay, done. What I see is a few particles with a lot of airspace
>inbetween them. I looked on the bb and tubes of my roadbike an counted
>3-20 particles per square cm. Doesn't seem like very much to me -
>seems to me like almost nothing. How can this be? My last ride was two
>nights ago, in the rain, longways thru Golden Gate Park from
>Haight-Ashbury to the beach and back. Off-roading my Vitus 979, I
>started to fall twice in mud and unclipped just in time to get one foot
>muddy. I also rode the spiral up to the top of the hill in the middle
>of stow lake - a dirt (sand) road up a sand dune - and again started to
>fall in the deep sand on top. I wished I had brought my CR250 instead
>and then rode back down. Then I continued to the beach and then home
>on pavement. When I got back, my shoe was clean, pedals were clean,
>cleats were clean, bike was clean. Except for the 5-15 pieces of sand
>per sq. cm with the occaisional 20.
>
>By 'thick with grit', how many particles per unit of area or volume are
>you talking about? And what is the relationship between those
>particles and the small ones which you think penetrate the rollers?
>Most of the ones I see on my bike are too large to get in there.
>
>dkl
Dear DKL,
The grit that damages chains consists of practically
invisible road dust particles, which are whipped up by the
tires and swirl around the chain.
While these particles are ridiculously tiny, they're still
just as hard as the original rocks from which they're
descended and will happily grind steel.
The dust sticks to any oily surface, just as flies stick to
flypaper. If the surface is an oily chain, the oil squishes
in and out (very slightly) of every nook and cranny as the
chain tightens, loosens, and swivels. This faint pumping
action gradually mixes filthy exterior oil with clean
interior oil.
(If the chain is waxed, the dust mostly bounces off the
non-sticky surface. Meanwhile, the wax slowly works outward
and never returns to the chain crevices from whence it came.
This one-way movement keeps the chain interior cleaner,
which reduces wear, but it also requires re-waxing to
replenish the lost wax.)
To see the invisible road dust, oil a clean chain, wipe it
off with a white paper towel, lay the towel aside, and go
for a ten mile ride. Wipe the chain off again and compare
paper towels.
The paper towel with the ugly black streak is smeared with
oil that has trapped road dust. The particles are so small
that you can't feel any grittiness when you rub the mess
with your fingers, but they eventually polish the chain
innards until a foot of chain wears enough to elongate a
sixteenth of an inch and needs to be replaced.
No matter how clean the roads may seem, even the air itself
ctonains dust. Run a damp paper towel along the top of a
window or door frame, and you'll see how much dust has been
drifting around inside the still air.
This omnipresent dust is why we go to all the fuss and
trouble of putting those apparently useless doors on kitchen
cabinets. Without the doors in the way, it would be much
easier to put plates away and then get them out again, but
it would also be much easier for the dust to get all over
the plates that you took the trouble to clean. Cabinet doors
are the domestic version of an enclosed bicycle chain--they
keep the dust out.
It's astonishing that such tiny particles suspended in oil
can wear steel chains, but we have to remember that a
slow-moving bicycle chain puts a very heavy load on a very
small part of each pin, so heavy that the metal surfaces are
expected to touch, despite any lubrication that we slather
on them. Keeping them apart under such loads would require
pressurized lubrication.
This raises a common misunderstanding about chain
lubrication. Professor Spicer's chain efficiency tests at
Johns Hopkins showed that only three main factors affect
power transmission--gear size, chain alignment, and chain
tension.
With a larger gear, the chain links swivel less as they feed
onto the sprocket.
With a straight chain run, there's no friction bending the
links sideways.
With more tension on the upper run that transmits the power,
the chain becomes more efficient.
(Unfortunately, this desire for more tension conflicts with
the desire for larger gears. At the same bicycle speed and
power, we produce more chain tension and efficiency by using
a higher, lower-cadence gear, which means that we're
wrapping the chain around a smaller, less efficient rear
cog.)
Chain efficiency was not affected by the choice of
lubricant. Spicer found that oil was a tiny bit better than
spray-on and wax, but the insignificant improvement was at
the limits of his measuring instruments.
In fact, Spicer found that lubrication has little practical
effect on chain efficiency. After cleaning with solvent, a
bare, dry, unlubricated chain transmitted 98% as much power
as it did with oil, wax, or spray-on lubricants. (Spicer
didn't mention it, but the dry chain probably squeaked like
a tortured bat.)
Spicer concluded that the chief function of the various
exotic lubricants that we debate here on RBT is really just
to keep road dust out by filling up the empty spaces inside
the chain. This agrees with decades of industry experience
with motorcycle primary transmission chains, which
essentially last forever because they run in a sealed oil
bath that protects them from the polishing effects of dust.
You can read Spicer's study here:
http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf
As for WD-40, the film of oil that remains after the solvent
evaporates is quite thin and light, so it tends to squish in
and out of a chain more easily than heavier oils, mixing
filthy outer oil more rapidly and thoroughly with clean
inner oil.
You can demonstrate this by spraying a little WD-40 on a
plate next to some motor oil and conducting a finger test
the next day. The remnants of the WD-40 will be much thinner
and easier to wipe off than the motor oil.
WD-40 is just too thin to fill up the empty spaces inside a
chain very well. What doesn't evaporate or run out is still
thin enough to squish in and out alarmingly well, mixing and
transporting trapped dust to the worst possible places.
Cheers,
Carl Fogel
