B55 vs B50

[Precurve]

Bought a couple of spools of B55 recently and made up some flemish strings for my recurve that I'd been shooting with B50.  The bow is quieter, with less vibration, likes a slightly lower brace and most noticeably, now likes about 50 grains less up front.  I don't own a chrono, but with the other changes noted you'd think the B55 must be shooting faster than the B50.  It sure seems like an improvement.  

On another note I gave a spool to a bowyer friend to try as he's running low on B50 and wanted to test the B55.  He made some endless loop strings and thinks the initial stretch is more than the B50.  My flemish results would tell me this is a stiffer string; with less stretch, not more but I haven't made the number of strings he has.  He made an endless loop B55 for me to try, and after an hour of shooting and 1" of adjustment it settled in, with about the same spine results as my flemish B55.  This endless loop wasn't a pre-stretched string so that 1" of stretch to settle in didn't seem excessive to me.  Anyone else have experience with the B55?

Dave

[LBR]

To me its a big improvement endless or Flemish.

[Precurve]

Chad;

What do you think of that 1" of brace height stretch initially on the B55 endless loop?

[George Vernon]

I think B55 is a great replacement for B50.  But remember, there is a difference between 'stretch' and 'creep'.  Stretch relates to 'elastic' changes in length when the material is strained or pulled.  When the force is released, the material goes back to its original length.  Think rubber bands.  There is some stretch in the string with just stringing the bow, but most of the impact of stretch comes into play during the shot.  Shooting an arrow does not remove all the stored energy from a bow.  Depending on the weight of the arrow, 10-20%, or more, of stored energy can be left in the bow. One way to handle the remaining energy is using the string like a spring on a car.  If the string can stretch, it can help absorb the left over energy.  If not, the limbs will take a jolt.  B50 and B55 do stretch more than fast flight types of strings.  Many folks feel they have a softer feel during the shot, but the stretch can also cause vibration and noise.  Nothing is free.

Creep is a change in length that is permanent.  So the increase in length stays after the straining force is removed.

B55 and B50 have about the same amount of 'stretch'.  But B55 has less 'creep'.

The change in length with new strings that people see comes from three sources.  One is stretch.  One is creep and one is the individual strands settling in.  This settling in change is most noticeable in flemish splice strings due to all the twisting involved in making the end loops.  The changes in length due to the strands settling in, like creep, is permanent.

I think most folks will find B55 gets to it's final length quicker and needs far fewer length adjustments to get to a stable brace height than B50.

[Wannabe1]

Thanks for sharing that! That is one of the best explanations I've read where I wasn't more confused at the end of reading!  

[LBR]

I agree for the most part...except less stretch doesn't cause more shock--you actually get less.  That's why some shock bows calm down with HMPE materials.  

The 1" could be the way it was made, PR some other variable.  BCY sends materials to an independent lab for testing and B55 was shown to have less stretch and creep than B50 or B500.  It still has considerably more than the HMPR materials though.

[LBR]

Sorry for the typos.  Trying to type on a phone.

[George Vernon]

LBR,
A point of clarification.  In my earlier post when I say the limbs can take a 'jolt' I did not mean to imply less stretch causes more hand shock.  No stretch strings stop the limbs very quickly. Some might call this a jolt or say they feel a solid 'thunk' at the end of the shot.  There is little or no buzz or vibration in the bow--little or no 'hand shock'.  The stretchy strings can take a while (a few milliseconds) to settle down.

Strings with stretch take most of the energy out of a bow when an arrow is shot by vibrating.  Some along their length due to stretch, some by lateral movement caused by standing waves.  High speed videos of a string during the shot cycle will show sine waves running up and down the string with substantial stretch along with noticeable side to side movement.  The 'waves' in a no stretch string are hardly visible.

Vibration in a stretchy string can transmit a buzzing or thumping kind of feeling to the bow hand. This is the 'hand shock' most folks talk about.  Some folks like the softer shot cycle of the srtetchy strings, but then have to choose a silencer to eliminate the buzz or thump.  Other's prefer the solid 'thunk' that comes from strings with little or no stretch.  To each their own.

There's considerable empirical and actual sound measurement data to show the same bow is almost always quieter when shot with a no stretch vs. when shot with a stretchy string.

Are there performance differences--yes.  Does it come from stretch vs. no stretch strings.  Well, I don't think that is real clear.

Most reports about string performance say the no stretch strings throw a faster arrow than B50/55.  A potentially confusing variable often not covered is the physical weight of the strings.  The no stretch strings have a strand strength much greater than B50/55 (dacron).  And the strand diameter is much less except for 450+.  So when strings of the same strength are made, the no stretch strings often have fewer strands and can weigh much less.  In most cases, I think the reduced weight of the string increases the arrow velocity more than a reduced amount of stretch.  When I test a stretchable vs. a no stretch string, and both are made to the same physical weight, the arrow velocity is the same within the repeatability of the measuring equipment.  

Now some folks have taken reduced strand count to an extreme and are making really skinny strings with 5-6 strands and then padding the loops and center serving to the right diameter to protect the bow nocks and be able to use commercial nocks on their arrows.

I have no doubt these strings are quiet.  Have no hand shock and are fast (they weigh much less).  But like all things in life, every virtue, when taken to an extreme, becomes a vice. Small strand count, skinny, strings are something I avoid.
I know a lot of folks think they are great.  But for me the hassle of padding and the risk of what happens when a strand or two is damaged is just something I don't want to get into.

[Precurve]

Thanks for the great, in depth observations guys!

[LBR]

Strings with stretch take most of the energy out of a bow when an arrow is shot by vibrating. Some along their length due to stretch, some by lateral movement caused by standing waves. High speed videos of a string during the shot cycle will show sine waves running up and down the string with substantial stretch along with noticeable side to side movement. The 'waves' in a no stretch string are hardly visible.  

I understand the logic, but I respectfully disagree.  The energy the bow produces is the same, regardless of the string (at least I think most of us would agree on that, except the magic string that gains 4# of draw   :D    :rolleyes:  ).

If the energy produced is the same, then the energy released is the same.  Sound and  vibration are the results of energy that didn't go into the arrow.  If it didn't go into the arrow, then it resonates down the riser and we call it "hand shock".  Some bows have considerable shock even with an HMPE string.

 

There's considerable empirical and actual sound measurement data to show the same bow is almost always quieter when shot with a no stretch vs. when shot with a stretchy string.
 

I'd love to see it.  I don't have the resources for such tests, i.e. a sound proof room to do the testing in.  All I can go with is my ears and what my customers tell me, which is tuning makes a lot more difference than string material.


I don't think there's a big difference in speed.  A couple of strands of string material weighs very little, then when you build up the serving to get the nock to fit you are adding a lot of the weight you saved right back to the most critical point on the string.  I've tried lots of "skinny" and low strand count strings.  I've never gotten any big differences, at least when comparing equally well made strings of the same material--shock, noise, speed are all very similar when the bow is tuned properly.


Chad