View Full Version : Clarification on Tension Discrepancies between Constant vs Lock-Out

08-13-2010, 03:22 PM
Something that's been bothering me lately is the tension discrepancy between constant pull machines vs lock out machines. Thus, I would like a bit of clarification/make sure that I am correct.

Is the difference that ultimately results in tension simply due to the fact that constant pull machines take into account the stretching of the string? Essentially, do all machines pull the same tension (say 60 pounds)? Then, when a lockout machine simply ceases to pull, tension drops due to the stretching of the string?

rich s
08-13-2010, 06:20 PM
Once a lock out hits the desired tension the machine quits pulling and string begins to lose tension because it is no longer being stressed by the tensioner.

A constant pull machine is constantly/continually applying tension/stressing the string so tension loss is delayed until you clamp the string when the tensioner is no longer stressing the string.

08-14-2010, 12:09 AM
Yss, assuming both machines are correctly calibrated then they will both initially pull to 60lbs. As Rich says when the lock-out reaches tension the brake pops and the tesnioner stops pulling tension and the string will start to try to return to its original state - thus the tension starts to drop. A constant pull machine like a drop-weight or electronic CP will continue to pull tension therefore reducing this loss of tension.

I (and many others) have found about 10% difference in reference tension is about right to match up from CP to lock-out or vice versa.


08-14-2010, 11:22 PM
Agree fully with the explanations above.

Because the elongation figures of strings are much more different than 10 years ago the difference in result between a lock out and a CP machine CAN be big.

I would advise crank users to select their strings very well on the elasticity and remaining elongation:
- Do not use stretchy polys because most of the stretch is remaining and will mean loss of tension.
- If you doubt about a string pull tension slowly, if you pull as fast as the string stretches a crank can get the same result as a CP.

As I just wrote on another post you can test the stretch qualities of strings very easily:
Clamp the end of the string in a bench vice and pull tension on the string by hand.
You can compare the elasticity and the total elongation of the strings very well.