Speed: Oh How We Love It!

Fast cars, fast computers, fast wide receivers, any kind of fast-action......we love it.  And when it comes to our archery equipment, it's no different.  Show most guys a brand new bow, and their first question is likely to be "How fast does it shoot?".  Right or wrong, speed is a major consideration for most archers.  And it's great to see how advancements in materials and design technologies have made today's compound bows better, faster, and more fun to shoot than ever before. 

Of course, there will always be a few dissenters in the crowd, those who'll loftily claim they don't care about speed.  But the market trends don't lie.  Archery consumers are taking advantage of these innovations, buying high-performance bows and speed-boosting gadgets by the trainload.  And nothing yields such a predictable and significant increase in speed like a good set of lightweight carbon arrows.  So let's examine the pro's and con's to shooting lightweight arrows.  Let's find out where they help, where they hurt, and where they don't really make a difference.

ARROW MASS AFFECTS ARROW VELOCITY

When all other variables are constant, arrow speed has an inverse relationship with arrow mass.  Of course there is a point of diminishing returns, but as arrow mass increases, arrow speed decreases.  As arrow mass decreases, arrow speed increases.  As we learned in Chapter 2, there is a limit to how light you should go, so it is possible to have too much of a good thing.  But the informed archer can greatly improve his bow's performance by upgrading to modern carbon/graphite arrow designs.  How much performance can be gained?  We put the issue to the test.


ARROW MASS VS. ARROW VELOCITY TEST

We prepared 9 arrows, ranging from 250 grains up to 650 grains in precisely 50 grain increments. Each arrow was fired from our test bow (60#/28" Bowtech Patriot) through the chronograph and the results were recorded (table below). Five trials were conducted for each arrow - to achieve a reliable speed measurement (average). Each arrow was fired from the same distance, from the same shooter, and without any modifications to the bow's settings during the test. The test was conducted at our indoor range, where lighting and environmental conditions could be held constant throughout our test.

FPS		Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Average
250gr Arrow	4.17 gr/lb.	294	294	295	294	294	294.2 FPS
300gr Arrow	5.00 gr/lb.	274	272	273	273	273	273.0 FPS
350gr Arrow	5.83gr/lb.	256	256	257	255	256	256.0 FPS
400gr Arrow	6.67gr/lb.	242	242	242	243	242	242.2 FPS
450gr Arrow	7.50 gr/lb.	231	231	231	230	231	230.8 FPS
500gr Arrow	8.33 gr/lb.	220	219	220	220	219	219.6 FPS
550gr Arrow	9.17 gr/lb.	211	210	209	210	209	209.8 FPS
600gr Arrow	10.00 gr/lb.	202	201	201	202	202	201.6 FPS
650gr Arrow	10.83 gr/lb.	196	195	195	195	194	195.0 FPS

OK.  BUT IS FASTER NECESSARILY BETTER?

Maybe.  From a standpoint of accuracy, you may find that lightweight arrows will yield some surprising benefits. From the moment your arrow is released from the bow, it begins to lose trajectory. As it succumbs to the effects of gravity and air resistance, it's flight path (trajectory) changes and the arrow eventually begins to drop back to earth.  Arrows which fly more quickly hold their trajectory better than slower arrows. So archers who shoot lighter-faster arrows will have less need to adjust for distance - since the faster arrows will hold a "flatter" trajectory within a given distance. In effect, the faster arrow allows you to make more mistakes in yardage estimation. If you mis-estimate a deer to be 25 yards away, and it is actually 30 yards away, a fast arrow "misses" it's mark by a much smaller margin. Look at the trajectory chart on the right from our Bowtech Patriot experiment. The heavier arrows nosedive much more quickly than the lighter faster arrows.  So whether you're a hunter or competition 3D shooter, you may find that faster arrows actually add a little forgiveness into your shooting, allowing you to make an error in yardage estimation without paying such a heavy price.

Hunters may also find that a faster arrow gives game animals less opportunity move out of position.  When you fire an arrow at a game animal, the sound of the bow travels much faster (about 1100 fps) than the arrow.  So the game animal will certainly hear the sound of the bow before the arrow arrives.  During that time, the animal has a brief opportunity to lunge, jump, squat, or otherwise get out of the way.  For example, an alarmed deer will often "crouch" in preparation to jump.  This crouching motion makes it appear the deer has attempted to "duck" the arrow, when in fact the deer is just loading it's muscles to jump and flee.  As a result, many bowhunters tend to miss high, shooting the arrow over the deer's back or impacting above the kill-zone, resulting in an unfortunate wound.  Of course, there are several factors that come into play (the alertness and athleticism of the deer, your distance and angle from the target, the amount of noise from your bow, etc.) which can affect how quickly a deer responds to the sound of your shot.  But one thing is for sure.  The faster your arrow arrives at the target, the less time the deer will have to react.  So let's take a look at how quickly an arrow traverses it's flight path, given a known distance and launch speed. 

So it seems to be a simple choice.  For the best possible performance, we just need to shoot the lightest arrow possible, right?  In most situations, yes.  But there's some other things to consider.  Most everything in archery is a trade-off; you have to give up some of this in order to get some of that.  The issue of arrow weight and speed is no different. Shooting an ultra-light arrow will indeed give you eye-popping speed, but at some expense.  

THE NEG:  MORE SPEED = MORE NOISE

First, shooting a lightweight arrow may result in a notable increase in noise from your bow.  It's to be expected, as the faster moving string makes a bigger disturbance in the surrounding air.  If you shoot a high-quality bow that's already pretty quiet, the difference may be subtle.  But if your bow is already noisy even when shooting your heavyweight aluminum arrows, shooting ultra-light carbon arrows will guarantee you a virtual harmonic train-wreck with every shot.  String silencers, Limb Savers™, and a good high quality stabilizer will all help, but be advised that added speed will typically come with some added noise too.  If you're a hunter, noise is an important issue.  But if you're a competition or recreational shooter, noise isn't such a serious issue.

THE BIG NEG:  LOSS OF KINETIC ENERGY

How much penetration, or knock-down power, your arrows will have is a matter of kinetic energy. Arrows which impact the target with more kinetic energy will penetrate the target more deeply than arrows with less kinetic energy. Kinetic energy is the energy of motion. Any object which has motion has kinetic energy. Total kinetic energy depends upon two variables: the mass of the object and the speed of the object.  And here's where the trade-off comes in.  A bow is generally more efficient, when launching a heavier arrow.  So mathematically, shooting lightweight carbon arrows will cost you a little Kinetic Energy (penetration) at the target.  To illustrate the point, we've converted our Bowtech Patriot experiment from FPS into Kinetic Energy.  Look at the results.

FT-POUNDS	Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Average
250gr Arrow	47.99	47.99	48.32	47.99	47.99	48.06 ft-lbs
300gr Arrow	50.02	49.30	49.66	49.66	49.66	49.66 ft-lbs
350gr Arrow	50.95	50.95	51.34	50.55	50.95	50.95 ft-lbs
400gr Arrow	52.03	52.03	52.03	52.46	52.03	52.12 ft.lbs
450gr Arrow	53.33	53.33	53.33	52.87	53.33	53.24 ft-lbs
500gr Arrow	53.75	53.26	53.75	53.75	53.26	53.55 ft-lbs
550gr Arrow	54.39	53.87	53.36	53.87	53.36	53.77 ft-lbs
600gr Arrow	54.38	53.84	53.84	54.38	54.38	54.16 ft-lbs
650gr Arrow	55.46	54.90	54.90	54.90	54.33	54.90 ft-lbs

As you can see, the heavier arrows manage more kinetic energy, or "knock down" power. But to gain just 4-6 ft-lbs of KE, you'll have to sacrifice perhaps 100 fps of your arrow velocity. Of course, every bow will not perform exactly as our test bow did. However, you can expect similar gains and losses in performance with most modern compound bow models. So this will be another trade-off to consider when ordering your arrows.  If you're a hunter, penetration is an important issue.  But if you're solely a competition or recreational shooter, don't give penetration another thought.  

This issue of KE is a major hot-topic of debate among bowhunters.  Some hunters setup their rigs to produce maximum speed, some want maximum KE, and others choose something in the middle.  Again, there may not be a right and wrong here.  Every hunter seems to have his own opinions on the proper techniques and ethics of big game bowhunting.  So with regards to lightweight hunting arrows and the real-world effect of the subsequent loss of Kinetic Energy, the following perspective might help.

SOME PERSPECTIVE: 

It should be noted that a properly placed arrow - impacting with 50 ft-lbs of KE would easily generate a clean pass-thru on large game like Whitetail Deer or Elk (as in our experiment with the Patriot above).  So with respect to kinetic energy and big-game hunting, there really is no practical difference between the 300 grain arrow impacting with 50 ft-lbs of KE and a 600 grain arrow impacting with 54 ft-lbs.  Either would make a clean harvest on big game.  So in most cases, the effective difference would really be how far the arrow sticks in the dirt after passing through the animal.

If you shoot a modern compound bow with at least 55# of draw weight, we suggest you not split too many hairs over the issue of KE.  If you do your job and place the shot properly, you'll have plenty of KE to make a quick humane harvest.  If you shoot mechanical broadheads, or you hunt "thick-skinned" animals like hogs, bear, or buffalo, some additional Kinetic Energy may be in order.