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"So,
when's the next installment coming out?"
That's a question I have been asked
so many times this season, I can't even count. And it is understandable
why so many have asked the question, considering our intentions
to complete the bike by the first race of the season. But since
the writing of the first article, several unforeseen and uncontrollable
situations forced us to alter our original timetable.
As the first event of the season
approached, it became apparent that it was not going to be possible
to have the bike completed within our limited amount of remaining
time. This was due largely to the fact that many of our parts
were special-ordered pieces, and there just simply weren't enough
days remaining to allow the manufacturers to deliver them to
us. Thus, we found ourselves in a dilemma because, while we
had an extensive project to be documented, we also had an AMA/Prostar
championship to pursue.
So, with about three weeks remaining
until Gainesville, we had to make the tough choice of putting
aside the new chassis, and making some minor updates to our
old, but proven chassis. We would then, as the season progressed
and new components were received, slowly integrate the new equipment
into the racing program. This would afford us a much better
opportunity to test and experiment with the new parts prior
to actually using them in competition.
We also decided to change the way
in which the buildup would be covered on Dragbike.com. While
our first intent was to cover the buildup on a day-by-day basis,
we felt that a different type of approach would give the readers
an easier-to-follow series of articles. Instead of day-by-day,
we will be breaking up the articles into groups of related components.
For instance, this installment will cover all of the basic frame
and suspension components. A later article will cover the completion
of the chassis, including mounting the body, brakes, etc. Down
the road, the engine buildup will be covered, followed by another
article covering all of the electronics.
So, now that everyone is up to
date on where we have been, and where we are heading, let's
get down to the business of building a dragbike.
THE CHASSIS
As was previously mentioned, our
old chassis was a proven design. When I say "proven",
I mean it had shown, over several seasons of competition, to
consistently produce some of the best 60' times in the class,
and an extremely stable ride further down the track. This level
of performance has come from years of experience and experimentation,
and those lessons learned would help us to build an even better
chassis for the new bike. But first, lets look at the somewhat
unique demands that the Formula Superbike rules place on chassis
design.
Unlike just about every other class
in motorcycle drag racing, Formula Superbike requires that production
frames be used in the construction of the bikes. So, while most
other professional class drag race bikes have specialty-fabricated
aftermarket frames, a Superbike has a production frame, with
an aftermarket, bolt-on swingarm. By limiting these bikes to
production frames, the cost of building a bike has been reduced.
Plus, and probably more importantly, it keeps the bikes in the
class more closely related to their, street-driven cousins.
They have the look and "feel" of being production-based
vehicles, much more so than other classes where full aftermarket
frames result in bikes that only slightly resemble their original
bloodlines.
Production frames are extremely
strong, but they are designed to yield that strength in ways
that do not necessarily reflect the needs of drag racing. That
is because the high horsepower levels, combined with a sticky
Mickey Thompson rear
drag slick, create loads in the swingarm pivot and engine mount
areas that far exceed what the factories ever envisioned their
bikes needing to sustain. In order to counteract the flexing
that results from this, a properly designed swingarm, with multiple
attachment points and plenty of bracing, serves to greatly stiffen
the stock frame.
For the construction of the swingarm,
we turned to Athanas
Race Chassis in Hyde Park, NY. Unlike many
other chassis/swingarm manufacturers, all products from ARC
are custom-built to the exact needs of the particular customer.
There are no off-the-shelf components from ARC, each one is
hand-built to whatever specs the customer desires. After consulting
with the owner, Todd Athanas, what we came up with would be
something completely new, and radically different than any other
swingarm we have ever used. The swingarm would be constructed
out of chrome moly tubing but, unlike most swingarm designs,
it would not use heavy rectangular tubing as the main structure.
Instead, it would be constructed entirely out of smaller diameter
round tubing, using structural design to attain rigidity.
As you can see from the accompanying
photos, what we ended up with is a very impressive piece. Instead
of being just a swingarm, it is actually a complete rear frame
section, similar to the back portion of a Pro Stock frame. It
is bolted to the stock frame at the top in the original rear
subframe holes, and is also attached at the bottom near the
original footpeg mounts. This serves to transfer the load across
the entire rear section of the frame, a far stronger method
than just using the original shock mounts. The long runs of
tubing along the top and bottom of the swingarm transfer the
load of hard launches not only to the factory pivot location,
but also to the top and bottom of the stock frame. Plenty of
diagonals and cross braces tie together what is actually rather
flimsy 1 inch diameter tubing. But despite the fact that the
tubing only has a wall thickness of .058", the structural
support created by all of the bracing results in an extremely
rigid unit.
Also, the pivot bolts have supports
that come both inside and outside the frame. This is to counteract
the uneven load that a single-sided chain drive design places
on the rear suspension. Under acceleration, the load on the
chain is constantly trying to pull the sprockets together. Because
this only happens on one side, the resulting load actually tries
to pull the rear wheel to the left side of the bike. To understand
how mounting the swingarm outside of the frame counteracts this
force, consider this: Imagine standing with your feet shoulder-width
apart, and having someone trying to push you from the side.
It wouldn't take much force to move you off balance. Now, move
your feet to about twice shoulder-width apart, and have someone
push you in the same manner. Your wider stance gives you much
greater stability against this force, just as the outboard (or
"clubfoot," as this design is also known) swingarm
mount gives greater stability against the uneven force of the
chain.
Another advantage
of this round tubing perimeter-style frame structure can be
seen for the accompanying photo. When viewed from above, it
is easy to see just how much room is available underneath the
seat area. Compared to a rectangular-tube swingarm , the open
area between the rear tire and the rear of the stock frame is
massive. And we will need it, because within that area we must
mount a large battery, the Schnitz
Ignitions Pro Series 2 ignition controller,
the
Motorcycle Performance Engineering
data acquisition system, and a very large oil tank for the dry
sump oiling system.
At the rear of the swingarm, ARC
installed a set of Pro Stock-style axle block assemblies, provided
by Precision
Metal Fab Racing. PMFR manufactures a number
of components for the serious drag racer, including wheels,
brakes, front ends, even complete chassis for the professional
class racer. Several components for this project were supplied
by PMFR, but for now, lets look at the rear axle adjusters in
detail. This style of axle adjusters is considerably stronger
than a conventional rectangular tubing adjuster. As an additional
benefit, these block assemblies allow for the rear ride height
to be adjusted. This is especially helpful in this application,
because the manner in which the swingarm bolts to the rear of
the factory frame provides no means to adjust rear suspension
height. The PMFR blocks will give us back the ability to not
only fine-tune the ground clearance, but also gives us an additional
method to tune the way in which the chassis reacts during hard
launches at the drag strip.
To complete the rear suspension
setup, ARC built a custom set of aluminum wheelie bars, which
bolt into the PMFR axle adjuster rails. This setup, as pictured,
including PMFR blocks, rear axle, wheelie bars, and footpeg
mounts, is available from ARC for only $800 racer price. Considering
the amount of detailed work involved in building this type of
swingarm, plus the fact that each unit is custom-built to the
customers needs, this is an absolute steal. It's no small wonder
why the majority of the bikes currently racing in the Formula
Superbike class use swingarms manufactured by Athanas. Other
styles of swingarms, including conventional rectangular tubing
units, are also available from ARC, just call Todd to discuss
your particular needs and prices.
Looking towards the front of the
bike, there are almost no modifications performed to the stock
frame. This is because the only allowable modifications within
the rulebook are limited to bracket removal and relocation.
The one exception to this is that the frame may be "raked",
which means that the angle of the steering stem may be increased.
This modification is frequently performed to drag race bikes
because it increases stability in the front end. It would take
too much time to fully explain the dynamics of how this works,
so let's just take for granted that the higher the rake angle,
the more straight-line stability will be present.
Of course, like most everything,
improvements in one area usually yield reduced performance in
another area. In this case, increased rake angles also result
in a bike with slower, heavier steering capabilities. For street
or road race use, which was the OEM's intended use, light, nimble
steering is a very important quality for their production bikes.
The factories build their frames with enough rake for safe,
stable operation, but no more than is necessary to maintain
light steering. Drag racing has exactly the opposite needs,
because the bikes simply have no need to turn. Instead, straight-line
stability is of utmost importance. This need is further enhanced
by the use of flimsy, soft side-walled drag slicks. These tires
cause a tremendous amount of instability at the rear of the
bike, and the resulting swaying and "wiggle" can cause
oscillations within the chassis. These oscillations can cause
"head shake", something most experienced riders have
had to deal with at one time or another. Increased rake angles
help to dampen and counteract these oscillations, and reduce
dangerous head shake.
Our previous chassis had the stock
steering angle still in it, but it was decided that this bike
would need to be raked. Not that we had ever experienced tremendous
problems with head shake, but it can be a bit unnerving when
the front wheel, which is carried several inched off the ground
for about the first 150', touches down at about 100mph. Because
the front tire is basically not spinning when it touches, it
actually skids for a brief moment when it first returns to the
track. The result is a bit of nervousness in the front end,
until the front tire catches up with the rest of the bike. Increasing
the rake would help to counteract this problem.
But there were other reasons why
the rake would be needed. As mentioned before, this bike will
also have a dry sump oiling system, which we will discuss in
detail later. For now, just understand that the oiling system
will allow us to run a nearly flat oil pan, giving us the ability
to lower the bike about 21/2 inches lower than the stock oil
pan would allow. To get some idea of how low this is, take a
look at the photo showing the complete roller chassis. That
wood block under the frame rails is only about 31/2 inches tall,
and the front wheel is still well in the air. Final ride height
will place the bottom of the frame rails a mere 21/2 inches
off the ground.
However, lowering the bike this
much creates new problems. With the stock rake, when we shortened
the forks as much as would be needed to achieve this ground
clearance, the front tire got so close to the engine that the
tire actually sat against the #3 exhaust tube. To further complicate
things, the tire was also sitting against the bottom side of
the lower triple tree. This left us no room for front suspension
travel. Definitely an unsafe situation, and far short of Prostar's
required 11/2 inches of fork travel. For this new chassis, in
order to take full advantage of the short oil pan, increasing
frame rake would be a necessity. By increasing the rake, the
front tire is moved further away from the rest of the bike,
giving us back the necessary room for the exhaust, as well as
the needed fork travel.
To perform the raking operation,
we turned to McIntosh Fabrications.
If you have never dealt with Terry McIntosh, give him a call.
He does some absolutely beautiful custom fabrication work, and
this rake job is no exception. The close-up photo hardly does
justice to his work, you must see it in person to appreciate
it. Terry doesn't just cut out the old neck, then reweld it
in a different location, but rather he completely removes the
original neck. In its place, a brand new billet neck is used,
complete with new bearing races already installed. Before the
new neck is welded in its new position, the frame is set up
in a fixture designed to keep the neck in perfect alignment.
This is critical, because if the neck is not parallel with the
direction of travel, a whole new set of handling difficulties
could arise. 
Once everything is mounted and
located in the fixture, the neck is TIG-welded in position and,
let me tell you, the welds are perfect. The frame is then allowed
to cool while still in the fixture. This is done because twisting
and distortion can occur during the cool-down process. The fixture
helps the parts to maintain their alignment while the temperature
of all of the various frame materials equalize temperature.
McIntosh also welds new tabs onto the front of the neck to mount
the headlight bracket, and also welds new steering stops. Our
frame does not have the stops or the headlight tabs because
we specifically requested that he not install them, due to the
fact that we need them mounted in different locations from stock.
But, unless you specify otherwise, these are included in the
job. What you get is a frame ready to be reassembled, with little
or no work required to reinstall all of the original components.
Looking again at the photo of the
roller, you can probably see that the angle of the forks is
increased. But also notice that, even with 5 extra degrees of
rake, the front wheel still doesn't appear to be way in front
of the bike. In fact, it is about the same distance from the
swingarm pivot to the front axle as it was stock. That is because
practically every bit of movement forward created by the rake
increase was counteracted by a set of front forks measuring
just 24 inches overall length. To provide us with a set of forks
this short, we again turned to PMFR. Their drag forks are absolutely
the best quality available, and have been time-tested by years
of use in both professional and sportsman-level racing. Each
component of the fork assembly is CNC produced from billet stock,
then carefully hand-assembled to the customers desired length
and width.
And talk about light! The set of
forks on this bike, including both triple trees, front axle,
and fork brace, weighs less than 12 pounds. That is several
pounds less than just one of the factory fork legs. But don't
be fooled by the light weight, they are incredibly durable.
I have personally witnessed many Outlaw Pro Street bikes wheelie
at 150+mph, then violently slam to the ground in a shower of
sparks. I have seen several front wheels collapsed, but I have
yet to see a set of PMFR forks bend.
Well that about covers it for this
portion of the frame buildup. Next installment we will complete
the frame by installing body mounts for the Beasley Fiberglass,
tabs for sheet metal panels and inner fenders, mounting the
brakes, and a whole list of small details. Until then, keep
an eye on our progress!
Installment
#1 of the Dragbike.com Formula Superbike
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