How do you think about speed rating for a rubber?

Michael Zhuang · Feb 4, 2022

If you bounce a ball on a rubber, you can directly see how far the ball bounces off the rubber, and this gives you a sense of speed.

But i think the grippiness also contributes to speed on topspin loops.

I have found some rubbers to be quite slow on a regular bounce, and yet incredibly fast in topspin loops.

I heard otcharov say something similar, that dignics05 is faster in first meter, but dignics09c is faster in 2nd and 3rd meter.

How do you think about what speed means for a rubber?

brokenball · Feb 4, 2022

It seems the forum has a memory of a gold fish.
This document explains most of what you need to know
https://deltamotion.com/peter/TableTennis/199408014 - Tiefenbacher - Impact.pdf
In short, it is all about the COR, the normal and tangential coefficient of restitution.

Read the second paragraph of the introduction. Nothing has really changed since this document was published in 1994.

dajdosta · Feb 4, 2022

Single digit speed rating of a rubber is inadequate. It usually relates to bounciness.
As you noticed some rubbers don’t have "gears", they are bouncy even on passive contact while some are slow and can feel dead on light contact but on hard hits they are fast. Hard rubbers have more gears usually.
D09C can be slow and controlled but very fast if hit hard with open blade.

igorponger · Feb 4, 2022

Schob pendulum is all you need. We got one from Alibaba, 35 Kilogramme freight shipping.

IB66 · Feb 4, 2022

The bounce test is just that really, it gives a very basic idea of how 'springy' the rubber/top sheet combo (rubber) is.

As for speed, its actually hard to tell, we observe what happens when we hit a ball, but we can't really put an actual speed or velocity in say meters / second to that shot, it's just fast / slow Etc.

As BB says we are not calibrated machines.

What I tend to do when testing or trying different rubbers (rightly or wrongly) is to see how far up the table the ball travels when I play a series of FH/BH drives / top spin strokes with roughly a similar amount of force applied to the strokes, this for me is a practical way to get an idea of roughly how fast the rubber / blade combo is.

Speed may be better assessed when you are actually on the receiving end of incoming shots!!! especially when different set ups are used in quick succession (twiddling between strokes). Then you get a good direct comparison between a couple of rubbers, Both 'pre' bounce and 'post' bounce.

Also the speed through the air compared to after the bounce can be vastly different depending on how much spin / what type of spin is on the ball before it bounces, how the table surface finish affects the ball after the bounce etc
for example, 2 tables, 1 has a surface that is 'grippy' allows the spin to 'grab' into the table, the 2nd is frictionless.
for a 'ghost' backspin serve, 1st table the ball grips, slows and then accelerates as it returns to the net, the 2nd table and the ball shoots off the end !!!
For a heavy top spin serve, 1st table the ball bounces and accelerates forward, 2nd table the ball just continues with (almost) its pre bounce speed / velocity.
So which table is 'faster' which is 'slower' ?? In this instance you could argue that the 1st table is both 'fast' and 'slow' depending on the spin on the ball !!!
The 2nd table would have less variation or effect on the balls speed after the bounce though regardless of the spin on the ball.
This also contributes to how we perceive the ball speed.

in an ideal world (for looping) I suppose you want fast through the air 'pre bounce' and faster 'post bounce' the greater the difference is, The greater the jump forward is, the better, but this is more down to 'spin' than 'speed'

We tend to associate speed or 'fastness' as 'I have to put in less effort to achieve a certain level/amount of ball speed, therefore the rubber is fast. but this is not the complete story!!! this is 'pre' bounce only!!!
You could have an extremely springy anti spin combo of sponge and top sheet, initially 'fast' pre bounce but no acceleration post bounce, as no topspin has been imparted on the ball during impact. Compare this to a rubber that is equally springy but can produce spin, initially both rubbers have the same pre bounce speed, but post bounce the ball that carries top spin is faster and 'jumps' / accelerates forward. Which is the 'faster' rubber???

The figures given by manufacturers, their speed and spin ratings must be based on some sort of testing, whether 'scientific' or human assessment ???? perhaps some of each!!

Can a ball accelerate differently ie T05 faster the 1st meter, D09C faster after 2-3 meters?? (all pre bounce?) BB over to you!!!

brokenball · Feb 4, 2022

IB66 said:
The bounce test is just that really, it gives a very basic idea of how 'springy' the rubber/top sheet combo (rubber) is.

The bounce test is a good test for starters.
Again, the forum has a memory of a gold fish. I has posted this too many times. It should be stickied somewhere.
Read the sports section there. The specifications for TT balls is given.
A metal plate is used because it doesn't absorb much energy.
https://en.wikipedia.org/wiki/Coefficient_of_restitution

But the OP is talking about rubbers not balls.
Again I would use a metal plate and a steel bearing that weighs the same amount as a TT ball and bounce the bearing off the rubber mounted on a steel plate. I would use a steel bearing for two reasons.
One, it won't deform and absorb energy like a TT ball would.
Two, it won be affected by wind resistance as much as a TT ball.
This means that only the TT rubber will absorb energy and affect the bounce.
The height of the bounce is related to the speed of the ball. Kinetic energy is (1/2)*m*v^2 and potential energy is mgh so it is easy to compute the normal COR based on the square root of the ratio if the rebound height to the initial height.

Measuring the tangent COR is a bit trickier. I would drop TT balls on a rubber moving horizontally using a motion controller ( I sell those ). The ball will not bounce straight up but the horizontal friction and springiness of the rubber will also cause the ball to move horizontally too. If the platform is moving horizontally at 5 m/s and the ball is moving .25 m/s horizontally after impact then the tangential COR is 0.5.

We are not calibrated machines but we can build one. The TT manufacturers don't care. If they did they would post true normal and tangential COR numbers. Also, these numbers would change as the thickness of the rubber changes.

Air resistance does play a part. Air resistance can be accounted for but it requires messing around with non-linear differential equations. A TT ball's speed will drop by about one half after 5 meters of travel. Yes, I did the simulation use non-linear differential equations. Until I retired I did this all the time.

This also contributes to how we perceive the ball speed.

How we perceive is irrelevant to the actual facts. So many times the customer will tell me this or that is happening after after looking at the data from a recording device they can see what they that was happening isn't what is actually happening. This is why we have high speed cameras and are able to capture motion do sub millisecond levels.

The figures given by manufacturers, their speed and spin ratings must be based on some sort of testing, whether 'scientific' or human assessment ???? perhaps some of each!!

Marketing overrules truth.

Can a ball accelerate differently ie T05 faster the 1st meter, D09C faster after 2-3 meters?? (all pre bounce?) BB over to you!!!

The ball only care about the impulse imparted on it. It doesn't care what rubber or stroke made the impulse.
Nothing is going to change after 2-3 meters because of the rubber. There is just wind resistance, gravity, viscosity and the Magnus force.

Michael Zhuang · Feb 4, 2022

igorponger said:
Schob pendulum is all you need. We got one from Alibaba, 35 Kilogramme freight shipping.

Which rubbers have you tested with this? what were your results?

Michael Zhuang · Feb 4, 2022

brokenball said:
The bounce test is a good test for starters.
Again, the forum has a memory of a gold fish. I has posted this too many times. It should be stickied somewhere.
Read the sports section there. The specifications for TT balls is given.
A metal plate is used because it doesn't absorb much energy.
https://en.wikipedia.org/wiki/Coefficient_of_restitution

But the OP is talking about rubbers not balls.
Again I would use a metal plate and a steel bearing that weighs the same amount as a TT ball and bounce the bearing off the rubber mounted on a steel plate. I would use a steel bearing for two reasons.
One, it won't deform and absorb energy like a TT ball would.
Two, it won be affected by wind resistance as much as a TT ball.
This means that only the TT rubber will absorb energy and affect the bounce.
The height of the bounce is related to the speed of the ball. Kinetic energy is (1/2)*m*v^2 and potential energy is mgh so it is easy to compute the normal COR based on the square root of the ratio if the rebound height to the initial height.

Measuring the tangent COR is a bit trickier. I would drop TT balls on a rubber moving horizontally using a motion controller ( I sell those ). The ball will not bounce straight up but the horizontal friction and springiness of the rubber will also cause the ball to move horizontally too. If the platform is moving horizontally at 5 m/s and the ball is moving .25 m/s horizontally after impact then the tangential COR is 0.5.

We are not calibrated machines but we can build one. The TT manufacturers don't care. If they did they would post true normal and tangential COR numbers. Also, these numbers would change as the thickness of the rubber changes.

Air resistance does play a part. Air resistance can be accounted for but it requires messing around with non-linear differential equations. A TT ball's speed will drop by about one half after 5 meters of travel. Yes, I did the simulation use non-linear differential equations. Until I retired I did this all the time.

How we perceive is irrelevant to the actual facts. So many times the customer will tell me this or that is happening after after looking at the data from a recording device they can see what they that was happening isn't what is actually happening. This is why we have high speed cameras and are able to capture motion do sub millisecond levels.

Marketing overrules truth.

The ball only care about the impulse imparted on it. It doesn't care what rubber or stroke made the impulse.
Nothing is going to change after 2-3 meters because of the rubber. There is just wind resistance, gravity, viscosity and the Magnus force.

Which rubbers have you found to have a high tangential COR?

I have found a new H3 sheet to have almost no bounciness. I thought maybe the tangential COR shows up in heavy topspin loops, but the ball seems to stick to the rubber and really doesn't project far even on topspin loops. The low tangential COR is despite the rubber surface being extremely grippy.

Big Dipper has good bounciness, and the tangential COR is fairly proportional to its normal bounciness.

Tornado V5 has low bounciness, but when I use it in topspin loops, I find the tangential COR to be greater than Big Dipper.

brokenball · Feb 4, 2022

Michael Zhuang said:
Which rubbers have you found to have a high tangential COR?

I am not a calibrated machine butI like Rakza 7. It probably isn't the spinniest but the ratio of tangential to normal COR seems about right for me. Rakza 7 is also relatively inexpensive relative to Tenergy or Dignics.
I am sure there are dozens out there that are similar to Rakza 7.
I think the spin/speed ratio of tangential to normal COR ratio is important. These ratios basically roughly define what you guys call "throw". Throw doesn't mean much. Throw is just an opinion, whereas CORs can be measured and compared.
H3 Neo is good for starters. It isn't fast and it doesn't do anything strange. There is little "trampoline" effect.

davizoosk · Feb 4, 2022

i think the higher the ball bounces on the rubber, i think it is faster, it also depends on the blade btw but normally very fast rubbers have a habit of the ball going out without making much effort, and also if you know how to control you can make good balls without much effort unlike the most Chinese rubbers, for me that's it.

brokenball · Feb 5, 2022

davizoosk said:
i think the higher the ball bounces on the rubber, i think it is faster,

That is what the equation mgh=(/2)m*v^2 tells us.

it also depends on the blade

NO, NO, NO!
Why to people on TT forums always try to confuse the issue with too many variables and themselves?
What part of testing the rubber mounting it on a steel plate didn't you understand?
This way ONLY the rubber gets tested.

btw but normally very fast rubbers have a habit of the ball going out without making much effort, and also if you know how to control you can make good balls without much effort unlike the most Chinese rubbers, for me that's it.

Yes, ESN and spring sponge rubbers are faster than most Chinese rubbers. It isn't a habit.

IB66 · Feb 6, 2022

Yeah testing using a metal plate etc will give a set of figures that can be used to show a rubbers characteristics. (And a sensible option!!!)

BUT what you put the rubber onto does have an effect, not on the rubbers characteristics but on the COMBINED characteristics, the whole ‘set up’ . This is why we make reference to the blade. The racket set up plays differently.
The rubbers characteristics haven’t changed, But COMBINED with blades that have different characteristics the OVERALL result is set up ‘a’ is faster than set up’b’
It is the BLADE that has made the difference to the COMBINED speed.

Its the SAME as COMBINING the same rubber top sheet with different sponges.
Each have their own characteristics, COMBINING them results in another set of COMBINED CHARACTERISTICS.

TTboy · Feb 6, 2022

This is quite a difficult topic since the technics of every player is different and a rubber / blade which is considered fast or hard is considered to be different from other players...

brokenball · Feb 6, 2022

IB66 said:
Yeah testing using a metal plate etc will give a set of figures that can be used to show a rubbers characteristics. (And a sensible option!!!)

[/quote]
BUT what you put the rubber onto does have an effect, not on the rubbers characteristics but on the COMBINED characteristics, the whole ‘set up’ . This is why we make reference to the blade. The racket set up plays differently.
[/quote]
WHAT ARE YOU TESTING? THE PADDLE OR THE RUBBER?
WHY DO PEOPLE ALWAYS CONFUSE THE ISSUE TO THE POINT WHERE THEY JUST GIVE UP?
If one rubber is faster than another then it will be faster on another blade.

The rubbers characteristics haven’t changed, But COMBINED with blades that have different characteristics the OVERALL result is set up ‘a’ is faster than set up’b’
It is the BLADE that has made the difference to the COMBINED speed.

If rubber A is slower than rubber B it will be so on ALL blades.

Its the SAME as COMBINING the same rubber top sheet with different sponges.
Each have their own characteristics, COMBINING them results in another set of COMBINED CHARACTERISTICS.

Would you stop and think a bit?
The ball bounces off the rubber slower than it impacts because the rubber absorbs energy. Blades absorb energy.
There is no adding energy that would magically make rubber B faster than rubber A.

brokenball · Feb 6, 2022

TTboy said:
This is quite a difficult topic since the technics of every player is different and a rubber / blade which is considered fast or hard is considered to be different from other players...

It is only difficult because you want to conflate everything into the problem at once.
The rubber or paddle doesn't change when you hand it from one player to a better player.
This has been a recurring problem on TT forums. It happens to a lessor extent on engineering forums.

So when the ball rebounds and is moving at a lower speed, it has lower kinetic energy than it did at impact? Where did this energy go if energy can't be created or destroyed?

How do you think about speed rating for a rubber?

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