Golf Shaft Spine

This is a summary from David Tutelman’s article “All About Spines”.

This article can be found in full on his website www.tutelman.com

“What a spine is and what it isn’t.

What it is:

Let's start by an explicit definition of what spine is. Here is my definition:

“Generically, spine in golf club shafts is the directional variation of stiffness.

More specifically, the spine is the direction of greatest stiffness of the shaft.”

RE: Spines. I do not like that name. More appropriate would be something like: “asymmetries in shaft stiffness”, but that’s not quite as catchy and as many people are familiar with the term ‘spine’, I will use it on that basis.

Since shafts cannot be built perfectly symmetrically, every shaft will be stiffer (more resistant to bending) in some directions than in others. This difference may be too small to be measured or, even if detected, too small to make a practical difference. But, given imperfect fabrication, the difference will exist.

Having said that, it is important to note what spine is not:

·      It is not some obvious physical characteristic, like welded seam of steel shaft. Actually, the name "spine" originally came from the belief that, since most steel shafts were welded tubes, the seam created an asymmetry in stiffness. But the welding seam isn't the only cause of spine, nor even the major cause.

·      It is not residual bend. Just as it is impossible to manufacture a perfectly symmetrical shaft, it is impossible to manufacture a perfectly straight shaft. Some shafts are straighter than others, just as some shafts are more symmetrical in stiffness than others. The bend of the shaft at rest -- with no flex forces on it -- is called the "residual bend".

Let's finish with a definition of the size of the spine. Remarkably little of the discussion of spine alignment addresses the fact that there are big, serious spines and then there are spines that are probably too small to matter.

“The size of the spine in a shaft is a measure of the difference between the stiffness at the spine and the stiffness at the NBP. It can be measured in CPM or in percentage difference of spring constant, depending on whether your measuring instruments use frequency or deflection.”

1cpm of frequency or 1% of spring constant is a small or even negligible spine. 10cpm or 8% is a rather large spine. The work has not been done to quantify where, between these numbers, is the "threshold" of spine importance, but it makes no sense to talk about aligning spine without also talking about the size of the spine.”

David Tutelman.