Cam Designs and why

by John Dudley
Cam Designs and why
I have a steady flow of questions come to
me each and every day through my
website. One subject of question that is
very common is Cams on compound
bows. There are lots of good questions
about cam types and positioning. Is this
cam better than that? Will this bow be
better if I use that cam? I am sure you get
the point. If you have a basic
understanding about cams you can
certainly help assure maximum
performance from your set up instead of
minimizing it. However you need to be
wise about it and stick to what the factory
has put in front of you as an option. Every
shooter has a certain need or certain feel
they are after and to be honest that is
why some companies offer such choices
to the consumers. Yes it may make you
slightly indecisive about what
combination to choose however the
results can be rewarding. I give credit to
Hoyt for offering such options to the
shooters. If any of you out there are in
the manufacturing business you will
definitely understand overhead and
inventory. Hoyt tends to overlook this
when it comes to cam options because
nearly every bow they offer has choices
on different cam types to choose from.
What I would like to do is walk you
through some of the cam choices
available and what the differences are in
these cams.
Before I go much further I would like to
mention something. Many of you want to
know the difference in Cams simply so you
can choose what bow configuration to
order, while others want to know so they
can make changes to the bows they already
have. I think changing a cam is something
most mid level archery enthusiast can do
and eventually will do. I think there is a
certain satisfaction that comes with taking a
cam from one model bow and putting it to
another model. It will make you feel like you
have designed something yourself. This is
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especially true if you try a combination that
isn’t available. I know because I have done
it. However, it is a false sense of creative
design. Reality is though that when it comes
to cams there is so much more to it that
meets the eye. I can assure you though that
the design teams that are in place inside the
walls of the factory have already concocted
every combination imaginable before they
released that bow to the market. Many of
them are good friends and I will vouch for
their brain capacities. The “CAMbinations”
that offer an advantage and are safe are the
ones they have as an option. Cams that
offer poor tuning, poor efficiency will not
make it into the catalog as an option.
Certain cams must go with certainly length
limbs and certain limb angles. You may
notice the parallel limb bows seldom have a
compatible cam system as a straighter limb
bow. There is a lot that goes into this and
the reasons are numerous so be sure to pay
attention to what the factory says for option
cambinations. I wouldn’t encourage you to
try cambinations outside the catalog or what
is recommended from the factory. It will not
only void your warranty in some cases be
potentially dangerous. With that said let’s
dive into some useful terminology and
information about Cams.
Common Cam Terminology
Let Off- I am sure most of you know what
let off is but I won’t assume all of you do.
Let-Off is a term that is used to describe
how the cam releases the difficulty of pull as
you reach the full draw position. This is one
of the many benefits to compound bows is
that the holding weight is much easier that
the pulling weight. With recurve bows this is
the opposite and why many believe to be
The
more difficult to shoot. The most common
let off options will be 65%, 70%, 75% & 80%.
For simple math I will use a 100 pound pull
and 80%let off as an example. As you pull
the bow the cam is designed to let-off 80%
of the weight you are trying to pull so once
you are at full draw you will only have to
hold the remaining 20% which in this
example would be 20 lbs. If the let-off is 65%
then you will have to hold the remaining
35% which would be 35#. Many target
archers prefer the lower let-off because this
forces to pull harder against the back wall.
The added holding weight usually helps
stabilize the bow and increase steadiness.
On the other hand the higher let-off option is
preferred by most Bow hunter’s because it
allows them to hold the bow at full draw for
a longer period of time with the heavier
pulling weight that is common with hunting.
A valuable thing to consider is that let-off is
usually designed into the cam by the
engineers during design. However we can
slightly change let-off by making changes to
the cable diameters. If you make the overall
diameter of the cables larger than factory
spec then you will intern lower the let-off.
Likewise if you make the cables diameter
smaller than the factory specs you can
increase the achieved let-off.
Valley- The Valley of the cam is the amount
of space you feel in the let-off between the
string going forward or backward. On older
bows with round wheels they had very long
valleys meaning you could pull it to full draw
and still be able to let the string forward
generously before it wanted to take off.
Many people referred to long valley cams as
feeling “spongy”. They longer valleys many
times are more forgiving to shoot but with
the cost of having lower performance. Most
of the cams today have shorter valleys with
Cam designs and why
a very solid wall. This is the preferred feel by
the highest percentage of archers because
overall performance is higher and proper
form is easier repeated. Some valleys
however are shorter than others. On very
aggressive cams with very short valleys it
will almost feel as if the bow will either be
getting pulled backwards or wanting to take
off forwards with literally no in between. You
are either pulling hard against the back wall
of the cam or the bow is shooting forward!
Some targets archers prefer this feel again
because it forces strong shots and perfect
shooting form. However a vast number of
archers may have a difficult time keeping up
with a very short valley especially when
combined with a lower let-off. The short
valley aggressive style cams are usually
offered as an option and not always the
standard option available.
Force Draw Curve- The force draw curve
is a plotted graph of the bows peaking force
or weight as it is pulled to full draw. The
further the bow is pulled the higher the force
increase until reaching its peak force and
then eventually falls lower again as the cam
let-off happens. The force draw curve will
reveal many characteristics of the bow it is
plotting. The shape of the curve will let you
know how quickly or slow it takes for the
peak weight to be achieved and also how
long it is sustained before falling off. When a
trained eye is looking at a force draw curve
they will almost certainly know the how the
bow will feel and perform before they have
even drawn it by hand. One of the most
important parts of the Curve is that it tells
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how efficient the cam is and how much
energy you get out of the cam as compared
to the energy you put in to draw it back. The
Easton Bow Force Mapper is available to
consumers and does a great job plotting
the Force Draw Curve. It gives a curve
reading the same as the machines top bow
companies uses which cost thousands of
dollars more.
Bow Mapper
Cam 1 & 2 plus
Timing/Synchronization- There is a lot of
marketing put into cam “timing” and why
some companies have advantages over
others. Personally I like to put all the hype
aside and say that for all cam systems on
the market there are still positions that make
the cams work more efficiently than others.
On the Hoyt Cam ½ system both cams are
slaved together with the control cable so
they argue the cams don’t have to be synch
perfectly to still shoot well. However, I still
say that having both cams reach the full
draw position at the same time assure peak
performance. On single cam bows they
advertise “no timing” which is true because
there isn’t another cam to time it or
compare it against. However they still have
cam “positioning or rotation” that greatly
affects the nocking point position, nock
travel, draw length and draw weight. If a
single cam changes in position all four of
those things are quickly affected resulting in
a change of accuracy or groupings. So the
The
bottom line is it is important to know your
cam system and make sure the settings are
in the correct place.
Comparing the available
Cam ½ systems
Cam1/2 Plus- This cam is based on the
original Cam ½ systems that Hoyt
developed 2003 but redesigned this year for
optimized higher performance including a
better force draw curves and higher speeds.
This very proven design and has so many
good attributes to offer any user. The Cam &
1/2 Plus™ has great speeds on all
configurations, is one of the easiest cams to
draw. One huge benefit to the Cam ½ and
Cam ½ Plus is the draw length adjustability.
The modules on the cams have settings A-F
that allow for quickly adjusting draw length
in ½” increments for 3 full inches of range.
For new archers and growing archers that
have not yet settled into a definite draw
length this is a great feature. I rate Draw
length as the #1 thing to have set correctly
in relation to shooting form. The adjustability
will help your local retailer quickly set the
bow perfectly to your size. This cam is very
forgiving and has a solid wall with an easy
shooting valley. This is one of the least
demanding systems on the market and has
numerous high level results due to the easy
shootability. It is available in 65% or 75%
let-off and can be changed by replacing
only the modules and not the entire cam.
Over a Dozen current Hoyt model bows are
adaptable with the Cam ½ Plus system. It
has been my experience that the highest
output of the Cam ½ Plus system are when
the modules are set in the E or F positions.
Spiral X Cam ½- This cam is also a newly
remodeled version of a previous Cam ½
system. The original Spiral Cam ½ was
designed specifically for the serious target
archer that preferred a high output,
demanding cam. It offered a rock solid wall
with a short valley and aggressive draw
cycle. The new Spiral X has been slightly
tweaked to perfect the original Spiral Cam.
This cam is going to give an easy 8-10 feet
per second when compared to the Cam ½
Plus system. The Spiral X has an aggressive
draw force curve and reaches peak weight
at a quicker rate than any of the other
systems. It is a fixed draw length cam that is
designed specially to the size you order it
in. Minimal adjustments can be made to the
draw length by modifying the strings and
cable length. Since the Spiral X is geared
specifically to the performance archer it is
only available in 65% - 55% let-off. What I
have found with the Spiral X Cam ½ is that
the valley is always fairly short. The feel of
this cam greatly changes from riser to riser,
limb to limb and draw length to draw length.
Nearly every combination will have a slightly
different feel. I have had my best results with
Spiral systems but prefer to shoot them
between 52-56#.
Bottom Cam synch - BAD
Top Cam synch - BAD
Bottom Cam synch - GOOD
Top Cam synch - GOOD
Spiral Cams
XTR Cam ½- This cam was designed
specifically to work well with the new XTS
limb available on the Alpha Max Series and
Turbo Hawk. I personally see this as the
best cam offered on short parallel limb
bows. The XTR has a very good draw force
curve and is very efficient. It has a
comfortable valley and a very solid wall.
This cam is only available in 75% let-off.
What I like most about this cam is that it is
also modular for draw length adjustment
and can be adjusted without the use of a
bow press. The XTR Cam ½ has a small
module that is held in position by two
screws that have been strategically placed
on the cam so that you can remove them
while the bow is at rest. I find that extremely
convenient to be able to adjust a cam length
without having to press the bow. The XTR
delivers high speeds over 320 fps on both
the Alpha Max 32 and the Turbo Hawk. On
my personal bow I installed a thicker cable
to lower the let-off slightly and used it for
target shooting this year.
XTR Cams
Autumn 2009
Z3 Cam ½- The Z3 Cam ½ was originally
designed for the Katera and Katera XL bows
that used the XT 500 limb. This cam is in
many ways very similar to the XTR Cam ½.
It pulls a smooth draw curve and has a
comfortable valley and a very solid wall. The
Katera series were also very fast bows and
achieved high performance from this cam.
There are still several Women and Short
draw archers making use of this cam on the
target scene. This cam is highly efficient and
continually delivers high speeds even at the
shorter draw lengths. This is also a fixed
draw length cam so the draw length must
be ordered exact. Unlike the XTR Cam ½
the Z3 offered both a 65% & 75% let-off.
Recently the Z3 Cam ½ has been
determined to work well with the Alpha Max
to achieve shorter draw lengths then
originally available. If you considered
The
Z3 Cam
shooting an Alpha Max but had a shorter
draw than what was available then you
should Contact Hoyt regarding this cam and
its ability to achieve shorter draw lengths on
the Alpha Max series.
M4 Cam ½- The M4 was initially designed
to fit the Mid Priced Hawk Series bows from
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Cam designs and why
Hoyt. This cam can easily be compared to
the Cam ½ Plus system. It is easy to pull,
with a comfortable valley and good wall.
The M4 is fully adjustable for 4” of draw
length. Much like the Cam ½ Plus the M4
has a rotating module system that is easily
changed to suit your length. This cam
however is only available in 75% let. I know
this cam pulls very nicely and is a forgiving
cam system to shoot. There is no doubt this
system was designed specifically for the
archer most likely to buy a mid level bow.
Speed on this system is rated at the
303-306 fps mark.
cam was designed for is the Trykon JR and
has a draw length range of 17-25”. I believe
it is very important to have entry level
archers use equipment that they are
capable of controlling. If the cam system is
too aggressive or the peak pulling weight
too high then it forces improper draw habits
that typically result in poor shooting
posture. This Cam is designed to perform
with this that in mind.
Versa Cam
Wrapping Up
M4 Cams
Versa Cam ½- The versa cam is really
designed with one thing in mind. A growing
young archer! This cam is adjustable up to
9” in range. It pulls easily for a kid and has a
long valley and soft wall. The bow that this
I know sometimes as a consumer it is
difficult when there is too many choices. I
know I can certainly have problems being
indecisive at times. However, options are a
good thing to have. For a manufacturer it is
an expensive thing to offer as well. I know
that in production companies there are very
few that decide to offer a lot of options and
customizing. For those that do though you
can have a good sense of individuality by
selecting something that is really
customized to fit your needs. I remember
ordering my first pair of custom Oakley’s
from the O custom shop and how special it
made me feel getting them. Did they protect
my eyes any better? NO, but I liked wearing
them more often because they were
something I put together with my mind.
A Placebo is a very positive attribute to a
competitor and customization is a very
good placebo. Who knows, maybe the best
shooting bow you will ever have is one you
help customize. Each and every Cam
offered from Hoyt has a certain feel, certain
performance and certain intention. Consider
the options and consider yourself and you
can certainly find a perfect match.
Good Luck…
John Dudley
www.dudleyarchery.info
www.ddbowhunting.com
Tournament Diary
13 September: Alton & Four Marks Archery Club’s 29th Annual Open Tournament.
Venue: Four Marks Recreation Ground, Uplands Lane Four Marks. Rounds: Windsors
(mainly for Archers who have not yet attained their 1st class, though experienced Archers
are most welcome to come along and shoot). Send SAE to: Kaye Garrett, 77A Victoria
Road, Alton, Hants. GU34 2DF. Tel: 01420 80481, or email to [email protected].
Details and entry forms can also be downloaded from our website:
www.altonarchers.co.uk
25-27 September 2009: Residential archery weekend at Green Park Centre, Ashton
Clinton, Aylesbury, Field, Golf, Clout & Novelties. For further details & entry form contact
Ian Millar at [email protected]
19-20 September 2009: The Ipswich International. Venue: Ipswich's prestigious Trinity
Park. The Tournament is open to all archers and consists of a World Record Status FITA
720 qualifying round on the Saturday followed by set format head to head matches on
the Sunday. Entry to the event entitles you to one 720 round and at least one head to
head match.
22 November 2009: ACA Worcester Tournament. Venue: The Agricultural Hall,
Lockmeadow, Barker Road, Maidstone, Kent. ME16 8LW. Details: SAE to Mrs Sandra
Punton, 577 Loose Road, Maidstone, Kent. ME15 9UH Tel: 01622 749960
In addition to the prize fund some major sponsors will be providing prizes for category
winners. In addition to the usual categories the organisers intend to have prize categories
that ensure that all entries have a realistic chance of winning a prize.The aim is to add
some innovation into the shooting calendar and if this event takes off you can be sure
that it will become a regular fixture that will no doubt grow. It's not often we get chance to
take part in something new so go on get those entry forms in. Further details can be
found at www.deben-archery.org.uk or email Steve at [email protected]
15-16 November 2009: Armistace Shoot; At the Marks, Speed, Cloth of Gold, Flight.
Venue : Scotney Castle, Lamberhurst, Kent.
Details: www.longbow-archers.com/keyeventsstgeorge.htm
12-13 December 2009: Christmas Pudding Shoot; At the Marks, Speed, Cloth of Gold,
Flight. Venue : Torry Hill Estate, Milstead, Kent.
Details: www.longbow-archers.com/keyeventsstgeorge.htm
3 January 2010: Welland Valley Archers’ Thirteenth Annual Indoor UK Record Status
FITA 18. Venue: Market Harborough Leisure Centre.
Details: www.wellandvalleyarchers.com or SAE to Paul Gash, 17 Oxendon Road,
Arthingworth, Mkt. Harborough LE16 8LA. Tel: 01858 525189 or [email protected]
21 February 2010: ACA Portsmouth Tournament. Venue: The Agricultural Hall,
Lockmeadow, Barker Road, Maidstone, Kent. ME16 8LW. Details: SAE to Mrs Sandra
Punton, 577 Loose Road, Maidstone, Kent. ME15 9UH Tel: 01622 749960
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The