The Carbon Fiber Incedent
Just as I was about to board the plane I noticed that the lady in front of me
was having trouble with her seat assignment. As with any plane boarding,
I was in the cattle line awaiting my turn to get a seat in the cramped
aircraft. I happened to be just at the edge of the jetway - the device
for boarding aircraft which is akin to a rodent habit-trail - when I
started to look at the metal used to make the planes outer fuselage. From
my insignificant perspective, the aluminum used to make the plane looked
real sturdy to me. I even grabbed an edge and attempted to see if it was
flexible. No, the metal would not be flexible without help from the "Jaws
of Life".
On the other hand, I knew this plane would buckle like a pinata if it had
to take any forces beyond those of passenger air travel.
Once inside the plane, I took my seat next to the lady with
seat-assignment woes. We sat near the junction of the wing and the fuselage.
She began to regale me with various stories about the stresses of
parenthood. I guess the stress of parenthood can effect anyone, but I found
myself more and more interested in the stress I saw on the aircrafts wing surface.
Take off
As we sped down the runway to a speed which would facilitate lift, I saw
the metal on the top of the wing surfaces appear to give a little. It was
similar to the first time you used a Seal-a-Meal. You knew the bag would
shrink up and look ugly, but somehow this was normal, no matter
how odd it looked. At some level I knew the metal on the surface of the
wing could take the forces of a 240MPH takeoff, but seeing the same
metal I was unable to bend actually giving way to unseen forces was a bit
eerie.
Once in the air I opened the latest edition of Roadbike-Mountain-Bike-Action-Carnage-Air-BMX Magazine
and tried to kill some time while waiting for
the plane to get where I was going. On every page was the newest,
strongest, and lightest part ever needed for your bike or MTB. There was
some stuff so lightweight it came with warnings about usage.
I started to correlate this with the metal on the outside of the plane.
The plane was designed to withstand the forces of flight within a given
set of parameters. That is, if you do not go over a certain speed, there
are no boulders on the taxiway, you have fuel, you are nowhere near
Mt. Pinatubo, and you do not land without the gear down, you will have
no problem getting the plane to go where you want. This is all coupled
with the fact that the pilot of the plane has had many hundreds of
hours flying a plane in the correct conditions. (If you haven't flown a
plane in the right conditions, you will not have hundreds of hours' practice!)
Now, if you change the parameters in which a plane has to work, you
can turn the most svelte aircraft into a big chunk of crap.
This started me thinking about the grey area in the middle of engineering
design, the area where a materials' rigidity meets flexibility and overall
weight. Most well-designed parts, in aircraft or MTB's for that matter,
have to compromise a bit in at least one of these areas.
The Incedent
My friend Phil bought a new mountain bike about 3 years ago. At the
time I was riding regularly on my beast - 30 pounds of bone-crushing
steel that would hammer over the roughest terrain without even a squeak
of complaint. I had no suspension yet, and the weight of my bike did not seem
of paramount importance to me. But, I was having problems with parts breaking everytime
I went riding. Phil kept going on and on about how light his bike
was. He had bought one of the first bikes that had carbon-fiber
integrated into the frame - a Trek. I tried the bike and had to admit it
was light compared to the beast, but I was not convinced it was worth
the $900 cost. The gears, brakes, and other components
were barely up to snuff with the parts I had on the beast (the parts I was
breaking eveytime I rode) when compared. But hey, this had a carbon-fiber frame. It was
supposed to dance circles around my beastie right??
Well, maybe.
After numerous talks about places to go riding, I finally got him
to agree to a park on Skyline Blvd.
This park had walking and riding trails, none of which are real flat in
any particlular place. I had also never ridden there before, so I figured
Phil and I would be better set to pace each other as I rode often
and he did not.
Everything started out OK. We began the ascent to the first leg of the
trail. Once at the top, Phil stopped and looked down the hill in
horror.
"Wassa matter?" I asked.
"I don't know about this trail. It looks real rough to me,". he said. He had that
look you get before you try your first "Advanced" ski run.
"Just go slow, pump the brakes, and you will have no problems," I told him. This was
not the first time I muttered these famous last words.
"What if the bike breaks?"
I tried to figure out what in the hell he was talking about. I have taken
a few serious falls. One was on a trail where I got
MTB riding and professional high-diving confused, and went off a rather
large fire road. In any case, I have broken levers, pedals, cranks, and
even a rear rim or two, but never an entire bike!
His trepidation stemmed from the 24 inches of carbon fiber which made up
the stay tube of his frame between the head and the top of the seatpost.
He was thinking that this light frame had compromised rigidity for weight.
On other words, he figured that a lighter bike could not take the same
abuse as a heavier bike with less "lightweight" material in it.
Knowing that Trek would not build a bike which was light and not somewhat
strong, I took the time at the top of the hill to describe the virtues of
frames and frame materials.
An Example:
The carbon fiber section of the frame was specifically chosen for the type of
stresses it took. Trek was able to measure the forces put upon the
top frame tube and determine that it took mostly shock from the headset
and the seatpost. Thus, a material that was strong in the same "direction"
would be sufficient, as opposed to a material which was able to take extreme
flexing or side deflection. In this case, carbon fiber was probably a perfect
candidate.
If you take carbon fiber and create the same shape as the carboard center
of a roll of paper towels, you will notice that you can push the object
from any end with a great amount of force. You could, for example, take
the carbon fiber tube and place it between you car and another car.
As long as you push in a straight line down the length of the tube, you
can actually push a car with this small carbon fiber tube. Now take the
tube and place it between the cars so you are pushing towards the center
of the tube from the sides. The slightest little force, and the tube
will break like it was made from balsa wood. This is part of the
compromise we deal with on all MTB parts. If you use the part within its
operating limits, it will perform like a charm. Push the part beyond the
limit, and you will have a chunk of garbage you still have to pay off on your
credit card bill.
Creating MTB frames is a science of balancing forces. Besides the forces
put upon a bike by the weight of a rider, you have the earth trying to
flatten out your rims, and deflate your tires. And, you still have to lean and
brake to go anywhere. All of this can put major stress on a MTB frame.
To create a MTB frame, you want to work with the forces which will be
hammering on your bike. To do this you need to think out a few details
like the frame geometry, the material(s) used to make the frame, and
the way the frame components are joined.
If you look in the latest MTB rag, you will see ads for all the latest bikes
and bike technology. Specialized has announced bikes with its
revolutionary M2 frame material. Trek is still sporting carbon fiber
and T1 aluminum frames, while other vendors work on the art of using Titanium.
(I say 'art' because Titanium is expensive and it is difficult to weld)
None of these bike frames are perfect. Some will do better than others,
and some just have too many odd handling quirks.
So what makes a good frame?
First the frame needs to fit the rider - this is the most important of
all. I cannot tell you how many times I have seen someone decide to buy
a new bike and the salesperson asks that great, all-loaded question "What
size frame do you want?"
Normally this question is followed by silence.
Without describing the entire girth of frame selection parameters, you will
want to choose a frame which suits you the best. On my ProFlex, I have a
20 inch frame. This measurement is determined by the length between the
bottom bracket and the place you would insert the seatpost. Being 6 feet tall,
you may need a 20 inch frame. You can look in any MTB magazine or book to
get parameters to assist in the fitting of a frame.
Another feature of a good frame is rigidity.
My beast is very stiff. In fact, this is the reason I chose the bike. My
motorcycling background had taught me that stiff frames were the only way to
win races and keep ones face from being buried into asphalt.
This is not true with a mountain bike. In fact, almost the opposite is true.
My beast is very stiff due to the materials used, and the way they are inter-
connected. Unfortunately, to get a real stiff frame you need to use a stiff
material. The beast is made of steel. You also have to weld the frame in
such a way that it will not crack. You see, if the frame is ultra-stiff, all
the forces acting on the MTB will be transmitted to other parts of the bike.
In my case these were the cranks, the wheel hubs, and the bars. The result of this
setup was about 3 years of broken bike parts.
Just so you know, I have gone through about 4 sets of rims and three rear hubs. And
until I got gel gloves, I was having severe pain in my wrists after a gnarly
ride. I have also broken three cranks; one was even stripped out from the center!
At one point it became painfully obvious that I needed to buy very strong
parts. Some of this was due to the fact that I was riding the beast like I
rode my motorcycle at the track - slides and all. The main reason
for my problems was that my frame had no give.
Now, reciprocally, I was able to use the ultra stiff beast to my advantage when
going downhill. Forays into the world of gravitational
decent allowed me to barrel down an incline like a skier
on qualudes. Because the frame was so rigid, the forces of rapid decent
had little effect on the beast. As long as I kept the rims from wheel-lock,
I could go downhill with the best of them.
Now that I have the ProFlex I have learned that a stiff frame is not all it
is cracked up to be. The ProFlex is not as stiff as the beast, it is
about 6 POUNDS lighter, and the slight give I get from the frame actually
helps me keep more of the Panaracers on the earth. This is also helpful when
one needs assistance from the "Blessed Mother of Acceleration."
My ProFlex is T1 alumimun (a lighter version of what was called Chromolly).
The T1 has exceptional rigidity for its light weight, and it is not very hard
to weld up tight. To minimize the flex, Girvin (makers of the ProFlex)
has used oversized frame tubes (like about 2.5 inches in a few places!) and
welds so "beefy" that you could put the frame in a car-crusher and you would
end up with the equivalent of a coke can and a handful of circular welds.
Light weight, careful frame geometry, and good welding result
in a bike which has enough give to keep the rims from deflecting under load,
while taking a downhill run like a rocket-sled. I also no longer need
to pump the brakes. I can go down with full binders on, and I get all the
grip I need (suspensions do not suck).
To be fair, you can buy a bike which has too much flex. Like some older
motorcycles (the Kawasaki H2 comes to mind), the flex is so bad I refer to
these bikes as being "hinged" in the middle. One way you can tell this is to
take your MTB for a test drive in a paved parking lot. Lean the bike
into a turn, and grab the rear brake.
A Science experiment
Does the front rim start to contact the brake pads??
You may hear some rubbing which is not present when you are riding upright.
Another test can be performed when the bike is not moving. Get off the bike
so that your feet are both flat on the ground. Close your legs so that you
have the top frame tube clamped between your manliness (or womenhoodliness).
Now grab the handlebars and try to bend them to the left or right. Do not
try to turn them, but pretend that you are trying to shear the bars off the
bike. On a bike you'd find at Walmart, you will notice that you can deflect the front
of the bike (the headset) as much as an inch off the alignment of the seatpost.
This is a bad frame, and it may even brake when you try to hammer on it real
hard.
Don't get Forked
Tom and Steve had gone out on San Antonio Rd. to ride on the paths by
the San Francisco Bay. Steve was talking up a storm about all the jumps there were, and
how fun it would be "table-topping" over them. Tom, being more competitive
than anyone I have ever met, figured if Steve could do it, Tom could do it.
Well, Steve could not do it. On one of the first jumps, Steve caught about
as much air as you'd find between the oil pan of a Ferrari and the pavement.
Of course, Tom made an attempt to follow suit.
Just as Tom hit the jump, the weld on his front
fork cracked, sent the front wheel into the frame and launched Tom into the
air like those freaks in the cannon at a circus. Tom had exceeded the ability
and engineering of his MTB. This was due in part to the fact that Tom
had bought one of the first Giant MTBs. When Giant first came out, they
were almost as well made as "department store" bikes. Now the Giant MTBs are actually
quite well made - on a par with Diamond Back, Trek, and the best of 'em.
Back to Phil.
We were still at the top of the hill, and Phil was beginning to sweat. It was
about 60 degrees out. I finally convinced him to make the decent, but he
was going to granny the Trek down the hill. I know what I would have done
with that bike.
We got to the bottom and Phil dismounted to see if any damage had occured.
Not to my surprise, the bike was fine, and Phil was relieved. Phil wanted
to go home.
About 3 months went by and Phil was one day telling my wife about "getting his bike
back." I asked him what had happened.
I figured he just was getting stuff adjusted. It seems that Phil had taken
a bail-out and the carbon fiber section of the frame contacted a rock and
was severly damaged. Thanks to good warranties, Trek had no problem replacing
the frame.
This is an example of another way you can exceed the engineering of a bike -
being paranoid and silly. If Phil had just relaxed everytime he went riding,
he may not have taken a spill, and the frame may have still been intact.
When talking to a friend, Pat, (who had the same Trek MTB Phil did),
I discovered that he was educated differently than Phil. When Pat bought his bike
he was told that the carbon-fiber Trek was not designed for beginners. It was
not a pro-bike either, but Pat was at least told that experience would keep
the bike from breaking, not luck. Pat was experienced, and to this day, I do
not believe that Pat has had any problems.
Oh ya, one last thing.
No matter what you buy, someone will come blowing by you like you are parked,
and they will be on a much less capable bike than you yours.
It is not logical, but it is often true.
Flyin Al
Got a question for Flyin' Al?
If you have any fishing or mountain biking questions for Flyin' Al,
you can send an email to:
aeb@adobe.com
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