PDA

View Full Version : ask DR.DAVE about the contact time.



pigbrain
07-06-2005, 06:25 PM
Is there any method that we can change the cuetip-cueball contact time, except an illegal shot. I have read many your .pdf documents, and i know the time is about 0.001s. but many people say they can make the contact time longer by some technic they can't tell clearly. I doubt.
and is there any difference between different impact points and different speed we stroke.

pigbrain
07-06-2005, 06:50 PM
and I am a chinese boy, i like billiards and also physics. i appreciate people like you who are working hard to discover the physical principles of billiards. and i gonna step on the way too. i personally collect your every articles but can i download your videos? i have not found out how can i download them.

Billy_Bob
07-07-2005, 06:26 AM
<blockquote><font class="small">Quote pigbrain:</font><hr> Is there any method that we can change the cuetip-cueball contact time... <hr /></blockquote>

I would suspect that a soft tip would have more contact time with the cue ball than a hard tip???

But then no one has ever experimented with different tips/shapes of tips with a robot *and* a high speed camera, so just guessing at this point...

randyg
07-07-2005, 07:18 AM
I believe that the "Jacksonville Experiment" answers those questions. Bob Jewett can help you here....randyg

Billy_Bob
07-07-2005, 07:42 AM
<blockquote><font class="small">Quote randyg:</font><hr> I believe that the "Jacksonville Experiment" answers those questions. Bob Jewett can help you here....randyg <hr /></blockquote>

They experimented with different tips and different tip shapes in the Jacksonville Experiment?

Scott Lee
07-07-2005, 10:10 AM
Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.

Scott

Billy_Bob
07-07-2005, 10:22 AM
<blockquote><font class="small">Quote Scott Lee:</font><hr> Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.<hr /></blockquote>

I was thinking more along the lines of a very soft tip as opposed to a very hard phenolic tip (not speed of stroke).

It seems to me that a very soft tip would initially hit the cue ball, then proceed to "squish in" - "absorb the shock" or whatever, and during this process, the tip would be in contact with the cue ball longer.

Whereas a very hard phenolic tip would have no give, would not squish in, etc.

I don't know, but it would be interesting to compare the two in a high speed video. (Actually I have a copy of the Jacksonville video and don't recall seeing any experiments done with different tips like this???)

Cane
07-07-2005, 10:46 AM
Read this thread and just had to try! LOL I wouldn't have thought it, but I can draw the ball well with a Lucasi House cue with a LePro on it(just the first one I grabbed out of the cabinet in my pool room) and with my Jerico Stinger Jump/Break cue (phenolic tip, very slight radius... nearly flat). Never would have thought that! Actually, the Stinger sucks the ball back VERY well on a power draw and I use it a lot on extreme masse' shots because of it's ability to spin the ball well without a miscue.

Of course, I'm not a robot, and no HS Camera, but, as they say, the proof is in the pudding. Pudding drew almost two table lengths with both cues.

As a matter of fact, Damn, let me see if I can do this! LOL I'm going to try to do a WEI table for the first time!

As an example of how well a phenolic tip cue can draw... In Tulsa, there's a little "game" that Gabe Owen, Shane McMinn and a few others play. The idea is to make the one, draw the CB three rails and make the ball in the corner pocket. It MUST be done with a phenolic tipped cue. I've seen them roll the money over time after time, because they all make the shot. It keeps going until only one makes it.

WEI Table (http://endeavor.med.nyu.edu/~wei/pool/pooltable2.html)

START(
%AI1Z9%BL7P8%CJ5O4%DL7N1%EM7P1%FK6P1%GK6N8%HM7N8%I L7O4%JK6M5
%KJ5P7%LJ5N2%MK6Q4%NJ5R0%OD1D0%Ph3V6%UJ5[3%Vg5V6%We3D2%XI5[2
%Yr6N1%Zf2C6%[e2[2%\s4O1%]E6E3%^d7[3%eA9b2
)END

I've tried it 20 or 30 times... made it a couple of times, but not consistently.

Later,
Bob

Chopstick
07-07-2005, 11:30 AM
<blockquote><font class="small">Quote Cane:</font><hr> It MUST be done with a phenolic tipped cue. <hr /></blockquote>

Why? I have never seen one of those tips.

Cane
07-07-2005, 01:50 PM
<blockquote><font class="small">Quote Chopstick:</font><hr> <blockquote><font class="small">Quote Cane:</font><hr> It MUST be done with a phenolic tipped cue. <hr /></blockquote>
Why? I have never seen one of those tips. <hr /></blockquote>

Chopstick. Maybe I should have stated that more clearly. It isn't that the shot can't be made with another kind of tip. The stipulations of the bet are that the CB must be completely behind the headstring, the first OB must be frozen to the rail at 1 diamond from the pocket, the second OB may be placed anywhere in or near the other corner pocket, the cue ball must travel 3 cushions before it makes the second ball and the cue used MUST be a phenolic tipped break cue. These guys seem to think it's too easy with a leather tip! Yeah right. I didn't EVEN ask if I could get in their little contest!

Later,
Bob

Bob_Jewett
07-07-2005, 05:30 PM
<blockquote><font class="small">Quote pigbrain:</font><hr> Is there any method that we can change the cuetip-cueball contact time, except an illegal shot. I have read many your .pdf documents, and i know the time is about 0.001s.... <hr /></blockquote>
The following increase the time of the tip on the ball:

A softer tip

A slower stick

Holding the stick tightly (but this effect is very, very, very small)

Using spin

A heavier stick

But you should first ask yourself why you want to increase the contact time. Some people think that by itself will increase the spin. It won't. If you want the ball to spin more, hit it further off center. That's much easier to control and has a much larger desired effect.

In fact, there are good reasons why you want to keep the contact time as short as possible to get more spin. Stated simply, if the tip is on the ball for too long a time when applying spin, it will drag on the ball (or tend to miscue).

pigbrain
07-07-2005, 05:49 PM
thank you so much! but want more experiments results. i dont think and am not eager to enlength the time. but some body kept telling me he can and can have a better control of cueball. can someone be so sensitive that if he stroke 0.002s he can tell its longer than 0.001s?
by the way i cant read many slang word.
what is the meaning of the sentence below?
"Hey boss. Let's shave him." - Puss n Boots

dr_dave
07-07-2005, 05:51 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote pigbrain:</font><hr> Is there any method that we can change the cuetip-cueball contact time, except an illegal shot. I have read many your .pdf documents, and i know the time is about 0.001s.... <hr /></blockquote>
The following increase the time of the tip on the ball:

A softer tip

A slower stick

Holding the stick tightly (but this effect is very, very, very small)

Using spin

A heavier stick

But you should first ask yourself why you want to increase the contact time. Some people think that by itself will increase the spin. It won't. If you want the ball to spin more, hit it further off center. That's much easier to control and has a much larger desired effect.

In fact, there are good reasons why you want to keep the contact time as short as possible to get more spin. Stated simply, if the tip is on the ball for too long a time when applying spin, it will drag on the ball (or tend to miscue).
<hr /></blockquote>
Great summary, Bob.

The only thing I would add is that for differences in contact time, we're still only talking microseconds (1/1000 second) or fractions of a microsecond. Also, some people think they can change the action of a shot by changing the contact time with changes in their grip or stroke mechanics. Based on what I've seen with high-speed video, I don't think this is possible. The only things that really matter for a given cue stick and shot are tip speed and offset from the CB center. Do you agree, based on your tests?

Dave

PS: Welcome back to the board! It seems that you've been away for a while. It's nice to have you back.

pigbrain
07-07-2005, 05:54 PM
one more question to Dr.Dave.
can i add a link to his video clips in my post in a Chinese BBS?

dr_dave
07-07-2005, 05:59 PM
FYI for you and others,

My August '05 instructional article (http://www.engr.colostate.edu/~dga/pool/bd_articles/aug05.pdf) describes many high-speed video results that are relevant to this discussion. Check it out. Also, The Jacksonville Project results can be checked out in Bob's collection of articles (http://www.sfbilliards.com/jax_bd150.pdf).

Regards,
Dr. Dave

dr_dave
07-07-2005, 06:06 PM
<blockquote><font class="small">Quote Billy_Bob:</font><hr>But then no one has ever experimented with different tips/shapes of tips with a robot *and* a high speed camera, so just guessing at this point...<hr /></blockquote>
I haven't experimented much with tip types and shapes, but I have tried a variety of grip and stroke types and speeds (e.g., see HSV A.35 through HSV A.59 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html)). Contact time does not change much with grip or stroke mechanics. The only important aspects of a stroke are cue tip speed at impact and how far the line of contact is away from the CB center.

Regards,
Dave

dr_dave
07-07-2005, 06:07 PM
<blockquote><font class="small">Quote pigbrain:</font><hr> one more question to Dr.Dave.
can i add a link to his video clips in my post in a Chinese BBS? <hr /></blockquote>
Feel free to link to any of my resources. That's why they are there, so people can have easy access to them.

Regards,
Dr. Dave

dr_dave
07-07-2005, 06:17 PM
<blockquote><font class="small">Quote Scott Lee:</font><hr> Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.<hr /></blockquote>
Actually, the contact time for most shots is closer to 1/1000 of a second (a microsecond). This is true for a wide range of shot types and speeds. One exception is with miscues (e.g., HSV 2.1, A.13-A.15, A.17, A.43-A.45, and A.54 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/index.html), where there can be sliding and multiple contacts between the CB and the cue tip, ferrule, and shaft. Another exception is masse shots (e.g., see HSV A.60 (http://www.engr.colostate.edu/~dga/pool/high_speed_videos/new/HSVA-60.htm)).

Regards,
Dave

ras314
07-07-2005, 08:43 PM
<blockquote><font class="small">Quote dr_dave:</font><hr>
Actually, the contact time for most shots is closer to 1/1000 of a second (a microsecond). This is true for a wide range of shot types and speeds. <hr /></blockquote>
Dr_dave, sounds like you must be a mechanical eng. type not used to working with small increments of time. /ccboard/images/graemlins/grin.gif

Actually 1 microsecond is .000001 second or 1/1000000 of a second. 1/1000 of a second is one millisecond.

Sorry just couldn't resist even though it probably doesn't make any difference to anyone. lol

Fred Agnir
07-08-2005, 06:32 AM
<blockquote><font class="small">Quote dr_dave:</font><hr> The only thing I would add is that for differences in contact time, we're still only talking microseconds (1/1000 second) or fractions of a microsecond. <hr /></blockquote> I'm sure you meant something else. Microsecond = 1 Millionth of a second = a thousandths of a millisecond.

Fred

Billy_Bob
07-08-2005, 07:18 AM
<blockquote><font class="small">Quote dr_dave:</font><hr>I haven't experimented much with tip types and shapes... <hr /></blockquote>

Something interesting to maybe try [for tip to cue ball contact time] is an 11mm "shaft size at tip" cue, a very soft tip (I think I used an elkmaster), and a dime radius on the tip.

Then whack the heck out of the cue ball with a very fast shot, almost approaching break speed. This will leave a concave "dent" in the tip. [Then the tip would need re-shaping of course before it could be used again.]

The opposite extreme would be a 13mm/14mm "shaft size at tip" cue with a quarter radius and a very very hard tip like a Tiger break/jump tip or even harder phenolic.

What I learned from my experimenting was that I liked the softer smaller dime shaped tip, but it did not maintain its shape very long, that a harder tip would maintain its shape longer, and that a tip on a larger diameter shaft would maintain its shape longer. (Don't want to be re-shaping my tip after every hard shot or in the middle of a match/tournament...)

And I have always wondered what is the best (ideal) tip radius for various shots? You could go from perfectly flat to very rounded dime shape or even an elliptical (egg shape).

Maybe there is a range in-between the extremes which works equally well. Or maybe one particular radius works better than others? Who knows??? FYI - Here are U.S. coin sizes...

Dime........ 18.00mm
Penny....... 19.10mm
Nickel...... 21.10mm
Quarter..... 24.10mm
Half Dollar. 30.50mm

dr_dave
07-08-2005, 12:13 PM
I stand corrected. This is quite embarrassing ... please don't tell any of my students. I certainly know the difference between "milli" and "micro" and use both of them quite often in my engineering work. Thanks for pointing this out. I'll try to prevent such brain farts in the future.

Dave
<blockquote><font class="small">Quote ras314:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr>
Actually, the contact time for most shots is closer to 1/1000 of a second (a microsecond). This is true for a wide range of shot types and speeds. <hr /></blockquote>
Dr_dave, sounds like you must be a mechanical eng. type not used to working with small increments of time. /ccboard/images/graemlins/grin.gif

Actually 1 microsecond is .000001 second or 1/1000000 of a second. 1/1000 of a second is one millisecond.

Sorry just couldn't resist even though it probably doesn't make any difference to anyone. lol <hr /></blockquote>

dr_dave
07-08-2005, 12:20 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote dr_dave:</font><hr> The only thing I would add is that for differences in contact time, we're still only talking microseconds (1/1000 second) or fractions of a microsecond. <hr /></blockquote> I'm sure you meant something else. Microsecond = 1 Millionth of a second = a thousandths of a millisecond.<hr /></blockquote>
Fred,

You are absolutely correct. I certainly meant "millisecond" (0.001 = 1/1000) per my brain-fart apology message (http://www.billiardsdigest.com/ccboard/showthreaded.php?Cat=&amp;Board=ccb&amp;Number=199966&amp;page =0&amp;view=collapsed&amp;sb=5&amp;o=&amp;vc=1).

Regards,
Dave

SpiderMan
07-18-2005, 10:28 AM
<blockquote><font class="small">Quote randyg:</font><hr> I believe that the "Jacksonville Experiment" answers those questions.<hr /></blockquote>

Randy,

Actually, I don't remember it addressing that aspect at all. I've watched the tape, and I don't believe tip hardness was a variable in any of the experiments. Bob?

SpiderMan

SpiderMan
07-18-2005, 10:30 AM
<blockquote><font class="small">Quote Scott Lee:</font><hr> Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.
Scott <hr /></blockquote>

Scott,

Where did you get this information? I would be really surprised to find that tip composition would not affect dwell time, but I'm unaware of quantitative experiments to determine this.

SpiderMan

Fred Agnir
07-18-2005, 11:21 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Scott Lee:</font><hr> Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.
Scott <hr /></blockquote>

Scott,

Where did you get this information? I would be really surprised to find that tip composition would not affect dwell time, but I'm unaware of quantitative experiments to determine this.

SpiderMan <hr /></blockquote>The Jacksonville Experiment did contain empirical data on dwell time based on a number of factors, including tip hardness and tip offset. The range reported for contact time was 0.8 milliseconds to 2 milliseconds. But, I don't believe there was specific tip hardness alone vs. contact time data. If that information is available for extraction from the videos, it might as well be presented to answer this question.

All that being said, that is a relatively small range of variance (1.2 milliseconds total) considering the number of paramaters people always bring up (stroke speed, tip hardness, tip offset).

The underlying question should be "what is the effect of tip contact time?" My quick answer is, the longer the tip contact time, the less spin or whatever people are looking for. Not more, but less. There's a couple of good reasons for why it would be less, but IMO, they ain't important.

Fred

SpiderMan
07-18-2005, 02:17 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Scott Lee:</font><hr> Randy...Why don't you just give Billy Bob the answer, which is NO. Different tip size, shape or hardness have no effect on the "dwel" time between tip and cb. It remains constant at around 4/1000's of a second...regardless of stroke speed.
Scott <hr /></blockquote>

Scott,

Where did you get this information? I would be really surprised to find that tip composition would not affect dwell time, but I'm unaware of quantitative experiments to determine this.

SpiderMan <hr /></blockquote>The Jacksonville Experiment did contain empirical data on dwell time based on a number of factors, including tip hardness and tip offset. The range reported for contact time was 0.8 milliseconds to 2 milliseconds. But, I don't believe there was specific tip hardness alone vs. contact time data. If that information is available for extraction from the videos, it might as well be presented to answer this question.

All that being said, that is a relatively small range of variance (1.2 milliseconds total) considering the number of paramaters people always bring up (stroke speed, tip hardness, tip offset).

The underlying question should be "what is the effect of tip contact time?" My quick answer is, the longer the tip contact time, the less spin or whatever people are looking for. Not more, but less. There's a couple of good reasons for why it would be less, but IMO, they ain't important.
Fred <hr /></blockquote>

Scott's source was 4 milliseconds, independent of "factors", but I've never heard that before.

BTW, why would longer contact time result in less spin?

SpiderMan

Bob_Jewett
07-18-2005, 04:09 PM
<blockquote><font class="small">Quote Fred Agnir:</font><hr> ... But, I don't believe there was specific tip hardness alone vs. contact time data. If that information is available for extraction from the videos, it might as well be presented to answer this question.
... <hr /></blockquote>
There was a "hardness alone" test. Hans de Jager had two tips that he felt subjectively were hard and soft. As I recall the center-ball contact time for the soft tip was about twice as long as for the hard tip. While we did not have a hardness meter, theory says that the tip would have to be about four times as soft to double the contact time.

Bob_Jewett
07-18-2005, 04:25 PM
<blockquote><font class="small">Quote SpiderMan:</font><hr> ... 4 milliseconds, independent of "factors", but I've never heard that before.

BTW, why would longer contact time result in less spin? <hr /></blockquote>
I have never seen a contact time as large as 4 milliseconds. The tip would have to be very, very soft and thick. Maybe a superball would do it.

If there is a long contact time, and you are trying to spin the ball, the tip will ride further around on the ball during contact than for a tip with a shorter contact time. To avoid a miscue with a long contact time, you have to start closer to the center of the ball. That means that the average distance from center for the hit is less. That means less spin on the ball.

One of the main revelations on the Jacksonville tape was the fact that the tip moves significantly to the side while on the ball when applying side spin. For another example of this, see the Austrian video clips:

http://www.bskunion.at/efler/Faszination_Dreiband_Windows_Media_9.wmv

The third sequence shows the tip moving to the side while on the ball. Notice also the large deformation of the tip, which is the kind of Moori that the shooter, Andreas Efler, normally uses.

In hind sight, it's obvious that the tip must move to the side during the hit, and the tip must be as free as possible to do so, unless you want more squirt.

SpiderMan
07-19-2005, 09:11 AM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> ... 4 milliseconds, independent of "factors", but I've never heard that before.

BTW, why would longer contact time result in less spin? <hr /></blockquote>
I have never seen a contact time as large as 4 milliseconds. The tip would have to be very, very soft and thick. Maybe a superball would do it.

If there is a long contact time, and you are trying to spin the ball, the tip will ride further around on the ball during contact than for a tip with a shorter contact time. To avoid a miscue with a long contact time, you have to start closer to the center of the ball. That means that the average distance from center for the hit is less. That means less spin on the ball.

One of the main revelations on the Jacksonville tape was the fact that the tip moves significantly to the side while on the ball when applying side spin. For another example of this, see the Austrian video clips:

http://www.bskunion.at/efler/Faszination_Dreiband_Windows_Media_9.wmv

The third sequence shows the tip moving to the side while on the ball. Notice also the large deformation of the tip, which is the kind of Moori that the shooter, Andreas Efler, normally uses.

In hind sight, it's obvious that the tip must move to the side during the hit, and the tip must be as free as possible to do so, unless you want more squirt. <hr /></blockquote>

Bob,

If this is true, shouldn't we notice an increased tendency to miscue with softer tips, for a particular "desired" amount of spin? I don't recall that being a common observation.

Also, if the softer tip "rides around to the outside", making it's effective offset greater, then is the resulting spin also greater? If that is the case, then could the softer tip achieve more spin with less initial offset? That would tend to negate the miscue difference.

Comparing two tips, I'd think that the important result would not be offset, but spin/speed ratio achievable without miscue.

I'd be interested in seeing an "iron willie" experiment that increased tip offset until miscue, and then recorded the spin/speed ratio just before this occurs. Are you aware of a quantitative experiment such as this, comparing various tips at the threshold of miscue?

SpiderMan

Bob_Jewett
07-19-2005, 10:09 AM
<blockquote><font class="small">Quote SpiderMan:</font><hr> ...

Comparing two tips, I'd think that the important result would not be offset, but spin/speed ratio achievable without miscue.
... <hr /></blockquote>
Theory says that tip offset is the main thing that determines spin/speed ratio. Do you think that something else contributes? Of course, some hard tips don't take chalk well.

I suspect that what's important is the average offset during the shot. If two tips miscue at the same final point, the softer one must start closer to the center of the ball and its average offset will be less.

Here's an extreme example: suppose one tip moves 10mm on the ball with a very long contact time and another tip moves only 1mm. If miscues occur at 20mm of offset, the first tip has to start at only 10mm of offset and will have an average offset of 15mm while the other (faster, harder) tip can start at 19mm of offset.

In any case, I think a focus on contact time is not useful.

SpiderMan
07-19-2005, 12:14 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> ...

Comparing two tips, I'd think that the important result would not be offset, but spin/speed ratio achievable without miscue.
... <hr /></blockquote>
Theory says that tip offset is the main thing that determines spin/speed ratio. Do you think that something else contributes? Of course, some hard tips don't take chalk well.

I suspect that what's important is the average offset during the shot. If two tips miscue at the same final point, the softer one must start closer to the center of the ball and its average offset will be less.

Here's an extreme example: suppose one tip moves 10mm on the ball with a very long contact time and another tip moves only 1mm. If miscues occur at 20mm of offset, the first tip has to start at only 10mm of offset and will have an average offset of 15mm while the other (faster, harder) tip can start at 19mm of offset.

In any case, I think a focus on contact time is not useful. <hr /></blockquote>

Probably not, but your assertions imply that there should be plenty of anecdotal evidence that soft tips are more prone to miscue.

Unless this is true, or unless some other dominant variable has been missed in this discussion, I think the jury is out awaiting results of some controlled experiments.

Where's that Predator rep that used to post here occasionally?

SpiderMan

Billy_Bob
07-19-2005, 12:33 PM
It seems to me that a harder tip would be more prone to miscue. And that a softer tip would grip the cue ball better because of the longer contact time.

I've certainly miscued when using english with a phenolic tip... (very very hard tip)

dr_dave
07-19-2005, 01:07 PM
<blockquote><font class="small">Quote Bob_Jewett:</font><hr>I think a focus on contact time is not useful.<hr /></blockquote>
I agree completely.

Dave

dr_dave
07-19-2005, 01:11 PM
I am shooting high-speed video this week. I already ran a bunch of center ball hits for various tips and speeds. I'll try to also film various tips at different offsets and speeds.

Regards,
Dave

<blockquote><font class="small">Quote SpiderMan:</font><hr> <blockquote><font class="small">Quote Bob_Jewett:</font><hr> <blockquote><font class="small">Quote SpiderMan:</font><hr> ...

Comparing two tips, I'd think that the important result would not be offset, but spin/speed ratio achievable without miscue.
... <hr /></blockquote>
Theory says that tip offset is the main thing that determines spin/speed ratio. Do you think that something else contributes? Of course, some hard tips don't take chalk well.

I suspect that what's important is the average offset during the shot. If two tips miscue at the same final point, the softer one must start closer to the center of the ball and its average offset will be less.

Here's an extreme example: suppose one tip moves 10mm on the ball with a very long contact time and another tip moves only 1mm. If miscues occur at 20mm of offset, the first tip has to start at only 10mm of offset and will have an average offset of 15mm while the other (faster, harder) tip can start at 19mm of offset.

In any case, I think a focus on contact time is not useful. <hr /></blockquote>

Probably not, but your assertions imply that there should be plenty of anecdotal evidence that soft tips are more prone to miscue.

Unless this is true, or unless some other dominant variable has been missed in this discussion, I think the jury is out awaiting results of some controlled experiments.

Where's that Predator rep that used to post here occasionally?

SpiderMan <hr /></blockquote>