IBO SPEED:  Let’s begin with our IBO Speed test. To obtain an accurate IBO Speed, several standard test conditions must be met. To begin, each bow must be set for exactly 30” draw length, 70# peak draw weight, and the test is conducted with an arrow weighing precisely 350 grains. Now…..that’s the basics, but when it comes to the business of selling compound bows, IBO Speed testing is a very serious matter. As such, the process of IBO Speed testing has become more of an art than a science. To learn more about the mysticisms of the process, please check out our help section for Understanding the IBO Speed Phenomenon.

For the purposes of our test, we don’t need to pull out all the stops. We just need to level the playing field between the two bows. And while we have no reason to suspect our chronograph to be inaccurate, we freely admit that it may or may not be calibrated perfectly - we don't know.  But for the purpose of this test, it won't matter if our chronograph reads a little high or low.  Regardless of any calibration error, our chronograph will treat each bow the same, giving us the data we need for comparison. 

So we setup each bow for exactly 30” draw length, 70# peak draw weight, and left each bow setup with it‘s standard let-off. We then installed a standard TM Hunter arrow rest and a single brass nocking point on each bow, but all string silencers and other accessories were removed for the test.

We then prepared a 350 grain Gold Tip 5575 arrow and setup our Competition Digital ProChrono Chronograph for the test. Standing exactly 2 arrow lengths from the Chronograph, we fired and recorded a series of 12 shots with each bow. To ensure the reliability of the data, the same person fired all 24 shots, and lighting and environmental conditions remained constant throughout the test. For each bow, our final speed score was established by throwing out the highest and lowest readings, and averaging the remaining 10 recorded speeds.

Special Note: Bowtech advertises an IBO Speed range, rather than a specific number. The Liberty is rated at 300-308 fps. So for the purposes of our computation we’ll use the middle of that range (304) as the Liberty’s advertised IBO Speed.  Our test results are listed below.

 

Chrono Test	T1	T2	T3	T4	T5	T6	T7	T8	T9	T10	T11	T12	AVG.
Bowtech Liberty (304 IBO)	294	296	293	293	292	294	292	294	294	293	293	294	293.4 FPS
Champion Diablo (315 IBO)	305	307	306	305	305	305	304	303	303	304	305	305	304.7 FPS

DRAW LENGTH:  This might seem like a moot point, as most bows (including our test bows) offer a considerable amount of draw length adjustability.  So if the draw length isn't right, it can simply be changed.  To that we concede.  However, this is a problem area for many manufacturers, and it's more of a pain in the neck than you might think.  All too often, we find draw lengths are LONG compared to their stickered rating on the limb - and this creates several problems.  To begin, most manufacturers publish their module charts for customer and pro-shop reference.  So when a customer orders a specific #6 module for his bow, then finds that the #6 module makes 27.5" rather than the 27" he wanted, he likely assumes something is wrong.  So draw length inaccuracies cause service problems and complaints.  Additionally, a pro-shop might decide to solve this little problem by adding or subtracting twists to strings, buss-cables, or control cables - essentially altering their lengths.  And this handy solution may indeed fix the draw length problem - but it can create other problems at the same time (cam timing issues, loss of efficiency, loss/gain of peak weight, nock travel issues, loss of let-off, etc.).  So it's much nicer if the draw lengths are just correct from the start.  Additionally, since longer draw lengths produce higher speeds, we sometimes suspect these inaccuracies aren't just a technical accident.  If a particular bow's 30" module actually makes 30.5", that may add an extra 3-6 fps to the bow's IBO Speed test.

So, how do we measure draw length?  The AMO/ATA has a very specific methodology for making this measurement.  Officially, a bow's draw length setting can be found by measuring the distance between the groove of the nock - to a position 1 3/4" forward from the pivot point of the grip - when the bow is at full draw.  Each of our test bows have arrived from the factory, pre-set and stickered as 30" draw lengths.  So the closer our measurements are to 30", the better.  The actual measurement is best done with a specially prepared arrow that has a graduated scale along it's side.  A square is used to locate the position that is 1.75" forward of the pivot point of the grip.  So now we just draw back and measure.  Holding from the bottom of the valley (not forcibly overdrawing either bow), our measurements yielded the following results.
 

LET-OFF PERCENTAGE:   Unlike a traditional Recurve or LongBow, Compound Bows are designed so the pressure required to hold them back DECREASES at the end of the draw stroke - sometimes dramatically.  So even though your bow may have a PEAK weight of 70# during the drawstroke, once you reach full-draw, you get the welcome relief of holding back LESS WEIGHT.  This decrease in weight is known as LET-OFF, and the greater the DECREASE in weight, the higher the let-off.  Let-off is typically measured in percentage.  So if a bow has a peak weight of 60# and 75% let-off, the shooter will only need to hold-back 25% of that weight (just 15#) when he's at full draw.  The remaining 75% of the weight will have been "let-off".  Easy enough! 

Though there is some debate in the industry about how much let-off is best, most shooters prefer MORE rather than less.  And now that Pope & Young has repealed their 65% let-off rule, the high let-off bows are sure to become even more popular.  So for the most part, it behooves manufacturers to advertise a higher let-off percentage.  Both the Liberty and the Diablo ETS have advertised let-offs of 80%. 

However, there's a bit of a technical snafu here too.  Depending upon how you compute the percentage, you can get two clearly different let-offs for the same bow, the "Effective" and "Actual" let-off.  If you would like to know more about hysterisis and let-off computation methodology, please click the link and read our help section.  That information is a bit too lengthy to include here in our shoot-out report. 

SO....using the data from our force-draw test (download this info - MS Works spreadsheet) we found the peak and minimum holding weights for each draw cycle.  The following results represent the ACTUAL amount of let-off they each have. 

PHYSICAL WEIGHT:   This was an easy one.  We wouldn't expect this spec to be fudged, as this is easily verifiable by anyone with a decent scale.  To conduct our test, we simply recalibrated our Weightronics 7620 Digital Package Scale and weighed each bow. 

Note:  Champion specifically notes that the Diablo's weight of 4.2 lbs. INCLUDES the Champion ISO Bar weighted dampeners (2) - which come installed standard on the Diablo.  As such, these items remained on the bow for our test.  Otherwise, ALL accessories and components were removed from both bows.

AXLE-TO-AXLE LENGTH:  This one should be a gimme' - another easily verifiable spec.  Keep in mind that your bow's A2A length isn't the same as overall bow length (as if measuring to fit the bow for a new bowcase).  The overall bow length will be longer than the A2A length.  To measure the axle-to-axle length you only include the distance between the axles as measured from their respective centers.  To conduct this simple test, we carefully measured from the center of the upper limb axle to the center of the bottom limb axle on each bow.  

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ROUND RESULTS:

So the Bowtech Liberty manages a narrow victory in round one - winner 10/9.  We were particularly impressed that both bows made over 96% of their IBO Speeds.  But we were surprised that both bows were well underrated regarding physical weight. 

SCORECARD:

         
          ON TO ROUND #2
          RING THE BELL  -------_>