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"WILL THE
REAL PARALLEL LIMB BOW PLEASE STAND UP!" |
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 TALK
ABOUT TERMS
Not since High School Geometry Class have we all heard
the word "parallel" so often. "Parallel" is the new
million-dollar word in the archery industry. In every
archery magazine, commercial, talk-forum, and
publication, the word parallel commands
attention. It's a full fledged industry buzz-word. The
phenomenon has even spawned a number of new parallel
phrases, such as..... parallel geometry,
parallel configuration, and parallel technology.
Strangely, a few archery marketing gurus have even
managed to quantify the parallel ideology, as
in..... near parallel, or
highly parallel, and the popular virtually
parallel. So whatever a highly parallel
geometric bow configuration is, we must desperately
need it. So perhaps it's time to take a closer look at
this innovation and to develop some way of measuring
just how much Parallel Force Quantum Alignment we
archery enthusiasts are actually getting.
PARALLEL LIMB ORIENTATION
Of course, the parallel reference is to the bow
design phenomenon we commonly know as Parallel Limbs.
Over the last few years, the Parallel Limb bow has risen
to become the apex predator in the compound bow market,
and every bow manufacturer now wants their piece of the
kill. But what is a Parallel Limb Bow? What
qualifies a bow as Parallel Limb?
Let's start at the top. Basically, a Parallel Limb
Bow is a bow that has a long riser and short swept
back limbs which are oriented horizontally (more or
less) at full draw. Unlike the limbs of a conventional
bow, which are oriented more vertically, the limbs of a
parallel limb bow angle back directly towards the
shooter. So from a side view, the limbs appear to
be......well.....virtually parallel to each
other. Hence the name of course. |
 GRADUAL
CHANGE TOWARDS TRUE PARALLEL LIMB ORIENTATION
Parallel limb bows didn’t just suddenly appear on the
market like a new cam system or camo pattern. The
development of parallel limb designs has been gradual.
As materials and machining technologies have improved,
some bow manufacturers have steadily tinkered with
longer riser lengths, shorter limb lengths, higher
limb-pocket angles and increased limb pre-load. So
particularly during the last 5 years, we’ve seen an
increasing degree of parallel limb orientation in the
new bow designs. |
 PARALLEL
SELLS
Anyone who has shot a parallel limb bow can tell
the obvious difference immediately. Compared to
standard bows with upright limbs, parallel limb bows
have very little recoil (and less noise). And the
flatter the limb orientation is, the smoother they seem
to shoot. There's no wonder why so many bowhunters
(especially) are opting for the newest parallel limb bow
designs. Virtually all of the hottest-selling bows on
the market are now parallel limb style bows.
Unfortunately, the success of the parallel limb bow has
created a number of parallel wanna-be's out there
- bows which are advertised as parallel limb but
clearly are not.....at least not close-enough to be a
genuine member of the club.
THE NEED FOR MEASUREMENT
It seems that any swept-limb bow can be adorned with the
label parallel limb. However, the various designs
certainly don't share the same limb angles. Some designs
are obviously much closer to being truly parallel than
others. So are consumers really getting what's being
advertised? Or is the label parallel limb being
used so loosely that any bow with a 70º+ limb angle is
now being sported as a parallel limb bow? Since
all parallel limb bows are obviously not created equal,
we think it's time for some reasonable standards of
measurement on this issue. |
 PRACTICALLY
PARALLEL TECHNOLOGY
Before we start talking about varying "amounts" of
parallel measurement, we should note that the word
parallel isn't a marketing term. It's a
mathematical term that describes the relative
orientation of two lines. By definition, parallel lines
extend in the same direction, they share a common
perpendicular, they are equidistant at all points, and
they must never converge or diverge. So two parallel
lines would never intersect, even if you extended them
forever in both directions like a set of perfectly
straight never-ending train tracks. Simply put, either
two lines are parallel or they're not. However, for the
purposes of melding the marketing with some some basic
measurement, we should define a true "parallel-limb" bow
as a bow with limbs swept back at 90º or greater (with
respect to the vertical axis of the bow) when the bow is
at full draw. |
 MEASURING
CHALLENGES
So, are there any bows on the market today which
actually have limbs that are parallel? Maybe. That's
what we're going to find out. But before we can declare
any particular design as truly parallel limb, we
first have to decide on a method of measurement.
Compound bow limbs aren't straight. They're installed
with some degree of pre-load (bend), such that a bow’s
limbs predominantly have a curved or arched shape even
when the bow is at rest. When the bow is at full draw,
the curvature of the limb increases. So the angle of the
limb, with respect to the bow's vertical axis, will be
different at the limb pocket than near the axles, and
the limb angles change as the bow is drawn back. So
this could get tricky.
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MEASURING THE LIMB
ORIENTATION
To get the best measurement of the limb
angles, we are going to focus only on the
last 4" of the limbs, where there is little
to no limb curvature. By carefully measuring
the distances between 4 points along the last 4"
of limbs, we are able to gather enough data to
compute the limb angles.
We begin by measuring and marking the limbs at
exactly 4" from the outside corners of the limb
tips. We then measure the distance between
points A & B and then the distance between
points C & D. As you can see, the resulting
ÐABD
certainly isn't a 90º angle, but this gives us a
nice regular trapezoid, and a basis to begin our
calculations. |
|
 |
| In this
example (2007 PSE Brute), line AB was 32.77",
and line CD was 30.19". Of course, we already
know the distances of line AC and BD are 4".
Now, to find the limb angle, we need to make a
right-triangle first. |
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To compute the limb angle
(ÐDBF),
we need at least two side lengths of right triangle DFB.
We know the length of line BD, and we can find the
length of line FB by finding 1/2 the difference of lines
AB and CD. Then we can compute
ÐDBF
with some basic Trig functions. |
|
 |
FB =
(AB-CD)/2
FB
= 1.125"
BD
= 4"
Ratio = ADJ/HYP = 1.125/4 = .28125
ACOS(.28125) = 73.68º
ÐDBF
= 73.68º
So we know that the at rest limb position
of the PSE Brute is 16.32º short of actually
being parallel (90º). So if we had to quantify
how parallel the Brute's limbs
are, we can figure it as a percentage and say
that the Brute's limbs are 81.9% parallel
(73.68/90) when the bow is at rest. So the
Brute isn't quite parallel when at rest. But
will the Brute's limbs be 100% parallel at full
draw? |
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|
 |
Using our Apple Force Draw Machine, we brought
our PSE Brute to full-draw, and then repeated
the same marks and measurements. The outer
measurement was 29.19" and the inner was
28.63". This yielded a limb angle of 85.99º,
which is surprisingly 95.5% parallel.
|
2007 PSE BRUTE |
|
At Rest L1 |
At Rest L2 |
Full Draw L1 |
Full Draw L2 |
|
32.44 |
30.19 |
29.19 |
28.63 |
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Limb
Tip Travel @ 29" Draw:
|
1.63"
p/limb |
|
At Rest
Limb Angle: |
73.67º / 81.9% |
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Full
Draw Limb Angle: |
85.99º / 95.5% |
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PARALLEL COMPARISONS
We repeated this procedure for the popular Fred Bear
Element and the new Diamond Black Ice to compute their
limb angles. As you can see, although each of these
bows are advertised as parallel limb designs, only one
of them actually reaches a 90º angle at any time during
the drawstroke. However, all three bows are within 5%
of parallel at full draw.
|
2007 PSE BRUTE |
2007 FRED BEAR
ELEMENT |
2007 DIAMOND BLACK
ICE |
|
 |
 |
 |
|
2007 PSE BRUTE |
At Rest
L1 |
At Rest
L2 |
Full Draw
L1 |
Full Draw
L2 |
|
32.44 |
30.19 |
29.19 |
28.63 |
|
Limb
Tip Travel: |
1.63"
p/limb |
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At Rest
Limb Angle: |
73.67º / 81.9% |
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Full
Draw Limb Angle: |
85.99º / 95.5% |
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|
2007 FRED BEAR ELEMENT |
At Rest
L1 |
At Rest
L2 |
Full Draw
L1 |
Full Draw
L2 |
|
32.88 |
29.88 |
28.50 |
27.94 |
|
Limb
Tip Travel: |
2.19"
p/limb |
|
At Rest
Limb Angle: |
67.98º / 75.5% |
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Full
Draw Limb Angle: |
85.99º / 95.5% |
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|
2007 DIAMOND BLACK ICE |
At Rest
L1 |
At Rest
L2 |
Full Draw
L1 |
Full Draw
L2 |
|
32.28 |
30.47 |
28.35 |
28.66 |
|
Limb
Tip Travel: |
1.97"
p/limb |
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At Rest
Limb Angle: |
76.92º / 85.5% |
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Full
Draw Limb Angle: |
92.22º /
102.5% |
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We also tested a random
sampling of a few other parallel-limb bows in the shop.
We even measured a non-parallel limb bow for
comparison. We've ordered them here, and classified all
bows with limb angles 90º or greater as Class AA
Parallel Limb Bows. Bows with limbs angles greater than
85º but less than 90º are called Class A parallel-limb
bows. Bows with limb angles greater than 80º but less
then 85º as Class B parallel limb bows. And any bow
with a max limb angle less than 80º is considered a
non-parallel limb bow.
|
Compound Bow
Make/Model |
Max Limb Angle
(@ 29" Full Draw) |
Percent of
Parallel |
Parallel
Class |
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|
Fred Bear
Truth |
94.0º |
BEYOND |
Class AA |
CLASS AA:
No significant hand-shock detectable at the
shot. Bow does not recoil away from your
hand upon release. Minimal forward limb
thrust. Excellent efficiency and speed. |
|
Parker
Frontier 2-Plus |
92.2º |
BEYOND |
Class AA |
|
Diamond Black
Ice |
92.2º |
BEYOND |
Class AA |
|
Browning Myst |
91.3º |
BEYOND |
Class AA |
|
Bowtech
Allegiance |
90.9º |
BEYOND |
Class AA |
|
Jennings CK
3.4R |
86.4º |
96.0% |
Class A |
CLASS A:
Very little hand-shock detectable at the
shot. Some forward limb thrust, but bow
remains comfortably stable at the shot.
Improved efficiency and speed. |
|
PSE Brute |
86.0º |
95.5% |
Class A |
|
Fred Bear
Element |
86.0º |
95.5% |
Class A |
|
Bowtech TomKat |
86.0º |
95.5% |
Class A |
|
PSE Firestorm
Lite |
82.3º |
91.4% |
Class B |
CLASS B:
Notable reduction in hand shock and forward
thrust compared to bows with standard limb
angles. |
|
Browning MC
Adrenaline |
81.9º |
91.0% |
Class B |
|
Diamond
Rapture |
81.6º |
90.6% |
Class B |
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Bowtech
Mission OBS |
79.0º |
87.8% |
Non-Parallel |
|
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PSE Triton NRG |
73.0º |
81.1% |
Non-Parallel |
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PARALLEL LIMB
REVOLUTION
Parallel limb bows appear to be here to stay, at least for a
while. For 2007, practically every compound bow manufacturer
has swept their limb angles back to keep up with the market
trends. Of course this is good news for archery consumers.
Since the entire market is soon to be flooded with these
designs, you won't need to spend $600+ just to get one. With
the majority of the manufacturers restructuring their line-ups,
the parallel limb designs can no longer be reserved for the
"high-end" bow market only. For 2007, there will be many
parallel limb bows in the $299-$499 mid-price ranges - so even
more shooters can enjoy the benefits of the quiet low-recoil
parallel limb designs.
WHAT'S THE NEXT "BIG
THING"?
The parallel limb secret it out, and no single manufacturer can
keep it for themselves. In fact, parallel limb bows are now the
industry standard, and we suspect the conventional D-shaped bows
are soon destined for the bargain bin. But that leaves bow
manufacturers, especially the "en vogue" brands, with a new
problem. How are they going to entice "high-end" buyers now?
What's the next "big thing" that will demand the premium price
tags? Carbon-fiber risers? Mag-Lev Cams? Who knows! Only
time will tell. But until the next must-have innovation
comes along, it's a bow buyer's market.
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PERSPECTIVE
 ARE
PARALLEL LIMB BOWS MORE ACCURATE?
Probably not. While the parallel limb bow is notably smoother
and quieter at the shot, there's no direct evidence to suggest a
parallel limb bow is inherently more or less accurate than a
standard D-shaped bow. In fact, target archery professionals
still prefer the more upright standard limb designs. Of course,
we must also consider that parallel limb bows tend to be short.
Target shooters generally prefer longer axle-to-axle designs.
And since target shooters aren't usually concerned about noise,
or recoil for that matter, the parallel limb bow isn't as much
of a phenomenon on the competition circuits. But for
bowhunters, it's a different story. Within a typical
bowhunter's range, a parallel limb bow is likely to provide the
same consistency and accuracy as any other style bow.
 DO
ALL BOWHUNTERS LOVE PARALLEL LIMB BOWS?
Certainly not! PLB's don't appeal to everyone, as they have a
few drawbacks of their own. While the generation-x buyers tend
to love the radical batwing shape of parallel limb bows, we hear
a number of more traditional buyers comment that parallel limb
bows are "ugly". And perhaps it's a fair criticism. For those
who appreciate the sleek lines and traditional appearance of a
bow, the parallel limb bow is no beauty queen. But the
criticisms aren't just about appearance (although we hear PLB's
have nice personalities).
PLB'S PRESENT EXTRA BOW MASS
As we mentioned earlier, parallel limb bows start with a very
long riser. Since most of the bow's weight is in the riser, the
parallel limb bow is typically 1/2 pound heavier than standard
D-shaped bows. In 2001, the average compound bow weighed just
3.6 lbs. Today, that average is well over 4 lbs. You may in
fact notice that the term "lightweight" has largely disappeared
from bow advertising. The dilemma is balancing weight against
structural stability. The longer a riser is, the stronger it
must be. So there is only so much material the manufacturer can
machine away (cut-outs in the riser) to reduce the riser's
finished mass. So for now, parallel limb bow buyers will simply
have to live with the extra weight.
BOW MASS PREFERENCES
Interestingly, adding some mass to the bow isn't automatically a
bad thing. Some shooters actually prefer a little more weight,
particularly competition shooters. A heavier bow tends to be
more stable at full draw and easier to hold steady while
aiming. So in that respect, PLB's aren't necessarily a step
backwards. On the other hand, some shooters clearly prefer the
lightest bow possible - particularly hunters who hike long
distances. Perhaps there is no right or wrong here, as this is
clearly a matter of personal preference. But let's keep things
in reasonable perspective. Less than 2 lbs. separates the very
lightest from the very heaviest bows on the market. And among
popular men's hunting bows, the difference from the lightest to
heaviest is about 12 ounces (the weight of a can of soda). So
even considering the extra mass of the PLB riser, your
fully-accessorized bowhunting rig will still tip the scales well
under the weight of your hunting rifle. |
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