As Reader's Digest is fond of saying, "It Pays To Enrich Your WORD POWER!" Here's the word for today: frisson. What's it mean? Nothing in English, but in French it means "shudder", more specifically the shudder that comes with a sudden realization or discovery. Here's an example. A couple years ago, I had the valves on my old Kawasaki Ninja adjusted. "You'll have a lot more power now that it's adjusted properly," my mechanic told me, so I headed directly for my local freeway and held the throttle open up to sixth gear. He was right---it had a LOT more power. I wanted to look at my speedometer so I could brag to my buddies about terminal velocity, et cetera, but I didn't quite have the guts to take my attention away from the road. After about two minutes and probably a touch more than four and a half miles of this ignorant behavior, I finally lost my nerve and decided to pull off the freeway for a Slurpee.
So there I was, sitting
on the curb at the 7-11 next to my bike, slurping away and doing
my best to look cool, when I noticed a spot of what looked
like dirt on the Ninja's fairing. I wiped it off. It was oil.
I followed the line of oil spots forward to the leaking head
gasket, then back to the, um, uh oh... The entire rear tire had
a light coating of Kawasaki motor oil. Those of you who own a
motorcycle or two are no doubt painfully aware of what oil on
your rear tire can do, but for the rest of my readers let me simply
state that it's not a good thing. The combination of high speed
and a slick tire could have wiped me off the NBL roster forever.
(Yes, I realize that not all of you would disapprove of that,
but try to look at it from my perspective.) The realization that
I had been, as Molly Hatchet says, "flirtin' with disaster"
caused a hideous chill to run up my spine. That's a frisson.
Not something I want to repeat.
When I (carefully)
returned the bike to my mechanic, he nearly killed himself trying
to apologize for his carelessness. "It's okay," I said.
"Nothing happened."
"It's not okay,"
he replied. "When you're on two wheels, everything has to
be right." That's the correct attitude to take. It
doesn't matter whether you ride a Honda VFR or a Dyno VFR---the
bike has to be in safe operating condition.
Now let's fast-forward
to a recent National. I'd just gotten done being a whipping boy
for Jorg de Louw, Paul de Pauw, and a bunch of other Dutch-sounding
dudes, when I saw a rider's head tube snap off during a mild landing.
The head tube weld breakage is perhaps the most common BMX frame
failure, but its effects are often nothing short of horrifying.
I went to the medics' tent to offer my worthless assistance and
saw the broken bike lying by the entrance. Both the top and down
tubes had the typical jagged edges that accompany weld failure,
but there was something odd on the down tube. I took a closer
look. Most of the broken weld surface was thoroughly corroded.
That corrosion hadn't happened in the five minutes after the accident.
When did it happen?
A quick check of the
book Light Metals by I.J. Polmear (Polmear I.J.; Metallurgy
of the Light Metals, Edward Arnold, London UK, 1989, ISBN 0-340-49175-2)
revealed the answer. It had probably been weeks, maybe months,
since the crack in this rider's frame had begun. With each
race, the crack spread around the tube, until less than half of
the original weld remained intact. Like the straw that broke the
proverbial camel's back, it only took one last small impact to
snap the down tube. When that happened, the top tube couldn't
withstand the shock alone, so it broke off as well. That left
the rider holding on to a set of unconnected handlebars, which
is as certain a prescription for disaster as exists in BMX.
Whose fault was this
failure? Was it the manufacturer's fault, for making a frame which
eventually cracked? Or was it the rider's fault, for not checking
the frame for cracks? Before you make a quick answer, ask yourself
the following questions: A)What type of material is your racing
frame made of? and B)How often do you check it for cracks? For
ninety-nine percent of riders in the NBL, the answer to A) is
either "Aluminum" or "Chromoly", and the answer
to B) is "Never." That's like going scuba diving, not
checking your air gauge, nearly dying of oxygen starvation, and
blaming it on folks who made your air tank. It's the manufacturer's
responsibility to make a decent product, but once it enters your
hands it's your responsibility to maintain and inspect
it.
A couple of months
ago in "BMX Basics", I opined that what "everybody
knows" is usually dead wrong. The conventional wisdom about
frame breakage is another great example of this. Here are some
more BMX myths to ponder:
"Chromoly frames don't break." Oh, yes, they
do. I've seen it happen a dozen times or more. I've seen frames
from nearly every reputable manufacturer break in some fashion
or another. All BMX frames wear out eventually. The physics of
a 150lb rider landing from seven feet up will eventually break
anything.
"Aluminum frames break without warning." Again,
this isn't true. According to Mr. Polmear's book, aluminum starts
to fail by developing microscopic cracks which get bigger and
bigger as time goes on. If you examine your welds and tubing,
you will catch frame breakages on the typical aluminum BMX frame
a long time before they happen.
"My (fill in the blank) tube broke on that jump."
I doubt it. More likely, the weld securing that tube broke.
Most people have no idea how strong aluminum or chromoly can be,
but if you take a look at a "steel-framed" roller-coaster
you'll get an idea. Tubing no bigger than what you'd find on a
BMX frame holds up several tons worth of people going very fast.
"I can ride this frame forever without any problems."
Sure, as long as you're mellow enough to not consider catastrophic
frame failure a problem. All frames fatigue. They will all eventually
break. Sorry about that.
"The weight limit on this mini frame is (fill in the blank)
lbs., but my son isn't a jumper, so it's okay to exceed that limit
a bit." It isn't always jumping that stresses frames.
It's balancing on the gate and blasting out of it. It's wrecking.
It's riding a rhythm section over and over again. Mini frames
wear out and break, too. If checking welds with a magnifying glass
after every race doesn't sound like your cup of tea, find out
the weight limit of your child's mini frame and stick to it.
I know that frame failure
is something you'd rather not think about. There are riders (and
non-riders) who are afraid to mention the subject, apparently
for fear that malicious Voodoo spirits will take some sort of
revenge on them. Like ostriches with their heads safely stuck
in the sand, these folks think that not looking at the danger
makes it go away. Also like ostriches, some people think that
if they flap their arms long enough they can fly. But I digress.
Frame failure is something that you can avoid if you are
willing to pay a little attention to your bike.
There are some very
specific warning signs that usually precede a broken weld or tube
on a BMX frame. These vary by frame material, so you have to make
sure that you're looking for the right thing. Take a moment to
go get your bike. If you have an aluminum frame, try to dig up
a magnifying glass too, but it's not absolutely required. Have
you got your bike yet? Okay, here goes.
If you have a chromoly
or high-tensile steel frame, begin by running your
fingers along the frame tubes, especially near the welds. Steel
tubing (chromoly is just steel with some other stuff mixed in)
tends to bend before it breaks. This is called straining.
If one side of a tube bends, the other side will buckle a little.
You should be able to feel both the bend and the buckle as small
bumps or dips in the tubing. Pay special attention to areas where
the paint or chrome has peeled or flaked off the tube; this is
often a sign of metal strain. Since the head tube and fork crown
are the most common failure areas, you should devote most of your
attention to this area, checking the top and down tubes where
they join the head tube.
Once you are satisfied
that your tubes are straight, take a look at the welds. Look for
dark hairlines where the cracks have begun. The edge of a old-fashioned
razor or scraper blade will usually catch in a weld crack, so
keep a blade handy for suspicious-looking areas. That's about
all there is to it. Once you know what you're doing, you can check
a frame pretty thoroughly in ten minutes or so.
If you have an aluminum
frame, you have an easier job. There's really no need for
check the tubes for bending, since most of the aluminum tubing
used in bicycles will break before it bends. You do need to be
more careful looking at the welds, however, since cracks seems
to spread faster in an aluminum weld than in a steel one. Using
a magnifying glass, if possible, examine the entire surface of
each weld, checking for the dark hairlines that usually signify
cracks. Like with the steel frame, a scraper blade will catch
in most significant cracks.
Don't be afraid to
take your time checking the welds on your aluminum frame, paying
special attention to the down tube weld. This is the most frequent
crack site, so you should examine it carefully.
If there are no cracks
in the welds, and you have some time, you can examine the tubing
for cracks. You should understand, however, that welds are the
most frequent failure area. Why? The heat of welding changes the
composition of the metal directly around the weld, usually for
the worse. It doesn't matter if you're working with steel, aluminum,
or titanium---welding weakens tubes. Since a bunch of unwelded
tubes wouldn't make much of a BMX bike, we have to put up with
that weakening. Exotic frame manufacturers like Santana Cycles,
builder of what many consider to be the world's finest tandems,
have some very expensive remedies for this weld-induced weakness,
but BMX frames simply aren't expensive enough to make this kind
of thing practical. For that reason, when your frame breaks it
will probably be at the weld.
How often should you
check your frame? It really depends on how secure you want to
feel. Once a week wouldn't be too often, especially if you ride
trails or street a lot. I recently had a major manufacturer's
team manager tell me that he was checking his riders' frames after
each National weekend. This isn't a bad idea. For the lazier riders
among us, checking once every three months or so might be enough
to keep the doctor away, as long as you are thorough about it.
If (or when) you find
a crack, there are a few things you can do, assuming the manufacturer
won't replace your frame. You can continue to ride the bike, which
will probably result in your injury. You could sell your frame
to another rider, which would be both legally and morally negligent.
You can have your buddy at the muffler shop re-weld the frame,
that's a bad idea; doing so will probably further weaken your
frame tubing and cause an even worse failure.
Last but best, you
could throw it away. I know you don't want to throw your four-hundred-dollar
frame in the dumpster.. The minute the paramedics pick you up
off the track, however, your medical bills will make $400 look
like small change. If you don't value your life enough to
"waste" that money, think of how much I, Jim Boswell,
need you to stay alive so you can continue to read my column and
feed my massive ego. Go ahead---open that dumpster and pitch your
crackmobile in. There's a good boy (or girl).
Remember the frisson
we were talking about? You'll feel it the first time you finish
a day clearing the big dubs at your local trail, come home, check
your frame, and find a big crack in the down tube weld. "What
if..." will be the first thing you think, but put it out
of your mind and start shopping for your new ride. BMX frames
aren't made to last forever. Come to think of it, neither are
BMX racing careers, but there's no reason to cut yours short,
is there?