SBS is String Bed Stiffness. What this tells us is the “stiffness” of the entire string bed, not just a single string. You may still hear the term ASPS, Absolute String Plane Stiffness, but that is too many words. How is this different than “reference tension”? Reference tension is the number you, the customer, tell your stringer to set the stringing machine to pull each string.
This “reference tension” has been the default conversation between customer and racquet technician for many years. The problem is that the SBS may not be even close to that number so as a racquet technician we need to know what the SBS is at a given “reference tension”. A device such as the Babolat RDC shown above can do this but it comes at a hefty price. The Beers ERT300 is
an electronic device that is available for around $150.00 and gives a number in Kg/cm, which can be easily converted to pounds. The FlexFour is another device that returns valuable SBS numbers. The point is be sure your racquet technician is using some device to record SBS. At Racquet Quest we use all three (3) so we can respond to any SBS request.
Without going into what happens to a string and racquet during the install process it is clear that the ball feels the “result” of all the strings acting in concert with one another and the racquet itself. So it makes sense to know what SBS (stiffness) the ball is “feeling”, and with this SBS number and the racquet stiffness number the “effective stiffness” can be calculated. Through manipulation of the SBS a “perfect” effective stiffness can be provided to you the customer.
So when you hear the term SBS you can quickly join the conversation and know what you are talking about! And, that is a good thing!