Happy to explain it for you, I just can't do so simply and quickly I'm sorry. My apologies for the length of what follows. 🙂
Different brands use different terminogy and reference scales to describe differences in blade speed, which creates a lot of confusion.
Ultimately however, I usually find they all measure / describe / compare / refer to the exact same key concept -- i.e.: a blade's coefficient of restitution ('CoR').
The CoR of a TT blade basically refers its ability to either reflect and/or absorb impact energy. Blades that reflect a lot of impact forces have a high CoR score, and are generally faster blades to play with. Blades that absorb a lot of impact forces have a lower CoR score, and are on the slower end of the speed spectrum.
Easiest way to measure a blade's CoR score is via the ball-drop test, but its a bit of a flawed model (more on this point later). To do the test:
- You secure a blade firmly and horizontally by the handle,
- You drop a ball from a known height onto its playing surface under static lab conditions
- You then measure how high the ball bounces after impact and
- You then compare the difference in these two heights to establish its CoR rating. (Established mathematical formulae exist to measure and quantify these qualities but please don't ask me to reproduce them here -- I've long since forgotten them. Its worth a Google however if you're interested).
The ball bounce test has a number of problems with it if you want to make precise comparisons however.
This method of measuring impact measurement is so far removed from a blade's actual operating environment, its virtually useless if you want to.make precise measurements:
• blades aren't fixed objects -- the test doesn't even remotely recreate actual playing conditions
• Blades aren't used bare. They always have rubbers attached which add their own hugely varying CoR values into the mix
• Any CoR figure you calculate will only be true and accurate for your test blade, at time of testing. Other blades' CoR scores are gojng to vary, even if they are the exact same model.
• the CoR of all woods vary with changes in residual moisture levels. These figures can and does change constantly due to shifts in relative humidity
• Even if you could and did accurately measure the CoR for your particular blade, that CoR isn't going to remain static over time. A blade's CoR typically decreases over time due to wear and tear from impact induced material fatigue
• blade CoR is also indirectly linked to a blade's mass, and mass can frequently vary considerably between individual examples of the same blade model.
• TT balls are hollow plastic spheres with very thin flexible walls containing nothing but air. As a result, a ball's inherent CoR will also change depending on the thickness and flexibility of its walls, and the temperature and air pressure inside the ball.
• the variability of wood density and grain affects CoR from blade to blade, so any resulting figure needs to accommodate margin errors appropriately.
• etc, etc, ad infinitum...
Long story short, accurately determining the COR of a single blade is a bit of a nightmare -- let alone doing it for thousands of different instances of the same model.
For all the above reasons and more, any *precisely quantified* speed comparison measurements, should be viewed with skepticism, and regarded as only a very rough guide.
These measurement scales exist only as a rough comparitive tool. Relying on them to accurately reflect very small differences in blade speed / CoR is ill-advised.
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[ PS: How blade makers
create and influence the CoR of their blade is another matter entirely.
The reasons why very different blade styles, with very different behaviours and paying feel can still have the exact same CoR score, is a fascinating subject to my mind. Happy to explain how that works too desired, but It lies outside the scope of your original question, so I decided to omit it this time round (It would have also doubled the length of my post 😂😂. )
Hope this helps. 🙂🙂
