String Bed Stiffness Riddle

Stefanm

Rookie
I have 2 Pure Drives (2015). One is about 2 years old and the other is a few months old. The older one is pretty beat. Both are approximately the same weight

I tend to restring them at the same time with the same string, tension, machine etc (Alpha with Wise)

For some reason the String Bed Stiffness (DT) of the newer one measures consistently 1-2 (kp/cm?) higher than the older one using a Beers ERT)

Does anyone have any theories why? Could the frame on the old one be "softened" up? I've noticed this the last 4 times I've restrung them. They definitely feel different when playing.
 

oble

Hall of Fame
Frames do soften over time, especially with heavy use. It probably deforms just a bit more than the newer frame when strung so that can potentially lower the DT by a bit.
 

esgee48

G.O.A.T.
Do you keep records of how often the older PD has been strung vs the new PD? Stringing places stresses on the frame each time it is strung. These stresses do create micro fractures in the frame leading to softness. Still, the DT should not be that much difference. DT of 1-2 units mean that the relative tensions are also different which means maybe you should check your grommets. I suspect that the grommets in the older PD have developed channels/grooves where the strings sit and that these may be creating frame/string friction that you may not be getting out when tensioning. I restring older Radicals all the time (in sets) for a customer and I take my time clamping after each pull. My customer's set always come out +/- 1/2 # of reference tension or less. I assume you move the crosses as you pull to remove interstring friction.

Wipe down the frame with polish to clean and make sure you get some of that polish into the channels of the grommets. 2 cents.
 

Stefanm

Rookie
The older one has been strung about 24 times. The current grommet strip has about 8 string jobs on it. The new one has been strung 5 times

I would have actually expected the DT for the very first string job on the newer one to be a bit low as the grommets would have not been completely seated , but it was not lower

Each racquet has been consistent in DT from stringing to stringing, it's just that one is consistently higher than the other

I do fan the crosses

Good tip on trying the polish. I'll try taking extra time in clamping the crosses next time as an experiment
 

esgee48

G.O.A.T.
I seem to recall that the portable ERT uses frequency to measure DT. This is just a throwaway thought. I am thinking that the older frame may be dampening vibrations a lot faster than the new one and if this is the source of your 'error.' I prefer to use Racquet Tune to check my tensions as soon as the frame comes off the stringer. Since I use the same strings almost all the time, it is not a big issue to get the tension via frequency. And I get the same tension(s) whether the frame/grommets are new or old. (I know that the brand new grommets will lose tension faster.) This does not answer your issue. If nothing seems to work, as a last resort, increase the tension in the mains and crosses by 3#.
 
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