clubheadspeed, smash factor and distance in ST

[Jon]

Can someone explain to me how the ST comes up with the numbers for clubhead speed, smash factor and distance? I think I read somewhere that ball speed is a measurement. Correct? What about the other 3 parameters I mentioned. Without measured results for clubhead speed and ball speed, wouldn't it be impossible to calculate smash factor and distance?

The reason that I ask is because I hit like 50 gap wedges yesterday and the clubhead speed seemed a little high for a 50* wedge: between 90 and 92mph The smash factor seemed low:between 1.0 and 1.1 (I was striking them solid) and the distances felt short:108 to 116 (I normally expect to carry my 50* 120). I've double checked the floor to make sure it is level and that the ST is at the same height as the ball. The only other environmental issue that I can think of is room light. I understand that too much light can be problematic for the ST, but what about too little? I set up my ST in an attic. After the sun goes down, the only light in the room comes from a small lamp and my iPad. Can this cause inaccurate readings from the ST?

[Clevited]

Skytrak directly measures ball speed, spin, vertical launch angle and horizontal launch angle, all other numbers are calculated. Skytrak uses its own algorithm for calculating carry distance. It also uses the parameters it directly measures to make a guess at your probable clubhead speed, then in turn that is used to calculate your smash factor. This will only even be close to accurate in my experience when the ball is struck dead on the sweet spot and your launch numbers are reasonable for whatever club it is.

If you post all of your numbers for the shots you are referring to (spin, vert la, ball speed), and if it was a solid center strike or not, many of us geeks on here can tell you if the distance you are seeing is reasonable or not, as well as the clubspeed and smash factor.

A few other tidbits. Remember to only look at carry distance not total, remember that mats and hitting indoors can greatly effect numbers you see outdoors, some find Skytrak to be a tad short possibly due to how it handles spin decay in its ball flight model.

Edit: I forgot about your lighting question. Its very doubtful that its causing you any issues. Skytrak can basically see in the dark with its IR flash. Only too much direct sunlight has ever caused me issues.

[Jon]

It is pretty disappointing that clubhead speed and smash factor aren't based on measurements. Are you aware of any published material that gives an explanation of how the ST comes to the conclusions that it does. The basis for those calculations. Carry distance isn't too much of a stretch since they do have ball speed and launch trajectory measurements. But without measuring club head speed or really having any club data at all, I can't imagine a possible way that they could come up with a smash factor. If ST could chime in and simply explain the calculation that results in these data points, it would be appreciated. Though, from my brief experience on this forum, they generally avoid the tougher questions about their product.

[skytrakali]

ST don't ever claim to measure club speed, and I think that they are pretty clear about that. As to how they try to work it out: I have backed this out. It's not too hard to do using standard Excel functions. Essentially for each club they have a set of coefficients that they use in linear fashion to predict club speed from ball speed, spin, and launch angle. This in turn gives the smash factor. In technical (statistical) terms it's a basic linear regression. No doubt the coefficients are created in the first place by looking at measurements of GC quad or something like that which measures ball and club and doing some simple fitting.

For the carry distance no doubt a system of coupled ordinary differential equations is used. ST probably have their own bells and whistles for the drag coefficients etc (everybody has their own versions) but I have no doubt that their model is VERY good. I doubt however that they include an equation for the evolution of the spin as the ball flies - this would be harder to do as the coefficients are less well known. There are many papers and quite a bit of literature on basic trajectory models, but the simplest public-domain introduction to the equations is probably

http://www.math.union.edu/~wangj/courses/previous/math238w13/Golf%20Ball%20Flight%20Dynamics2.pdf

Flight is relatively easy, but roll is much harder to model, so here ST probably uses some pretty simple laws. You only have to look at golf on TV to see how the roll parameters depend crucially on the course conditions. In any case, I find that it's CARRY that's the crucial parameter. That's what I really care about.

[aja]

"Smash Factor" in any case cannot be measured. It is an artificial concept based on the clubhead speed and resultant ballspeed. It is a theoretical value.

[skytrakali]

I never found smash factor that helpful a concept actually. But if people are interested then there' s a very neat little article at

https://www.tutelman.com/golf/ballflight/smashfactor.php

which shows (i) that the theoretical maximum smash factor is 2 (OK you need an infinitely heavy club, zero loft, perfectly rebounding ball etc etc) and (ii) that in practice even DJ or Rory is unlikely to ever get a SF as high as exactly 1.5

[Clevited]

Just to add to that, I have read some articles that suggest that the industry standard Trackman, often measures club speed closer to the heel of the club rather than the center. This inflates many of their SF numbers. From that and just looking at the math, the realistic max SF for a driver for instance will be 1.49 not 1.52, 1.53 like you often see. Only hot faces, a really heavy clubhead or illegal golf balls could actually produce that from what I have researched.

[skytrakali]

Yes, agree absolutely. I was surprised by how much difference it can make to SF whether you measure the speed of the heel, toe, middle, top or bottom of the club, but the numbers are clear. "Club head speed" is not a carefully defined data item unless you say exactly where you are measuring it!

[Clevited]

Measuring clubhead speed directly with a camera based system is really hard I think. Thats why Foresight does it with a separate unit and stickers on the clubface. Skytrak has no possibility to do this directly wirhout an add on of some sort. Best they can do is improve their method for guessing what it is which they are supposedly working on.

[jut111]

You don't need clubhead speed or smash factor to accurately calculate carry. You need what ball speed, launch and spin. Skytrack directly measures those variables

[Jon]

I get that smash factor isn't needed to calculate carry distance and apparently no one else really cares that the smash factor numbers in the ST software are pretty much garbage. Here is what I don't get. Why does ST need to add all these parameters that are based on some ghost algorithm that no one has actually ever seen before. I think skytrakalli mentioned above "never found smash factor to be that useful anyway" Smash factor tells you how solid you hit the ball. In what world is that not useful information? Adding these bogus data points like club head speed and smash factor (with results that rarely have any basis in reality) only serves to water down the product as a whole. If ST had some kind of groundbreaking algorithm hocus pocus that actually produces accurate results for club head speed and smash factor, that would be great. But that is not the case. I'll hit 30 shots in which 20 were hit about as solid as I am able to, and the smash factor will read between 1.05 and 1.15 for all 20 shots.
At very least, I think parameters that are based on anything but measurement or a sound and tried method of calculation should be in a different color or have an Asterix next to them. It's like a high school sophomore trying to make her bust more substantial by stuffing her bra. At some point, you find out what is under the hood. If you don't find that disappointing, I've got to wonder why you are on this forum.

[Clevited]

Skytrak are working on the hocus pocus algorithm as we speak supposedly. I have proven that you can indeed pretty accurately calculate clubspeed if you know the relationship between spin, ball speed and launch angle. I half arsed my little calculator and I am still more often than not, obtaining very reasonable numbers, often only off by 2 mph. If I can do that in my free time, I think Skytrak could potentially create something better yet. Of course this method absolutely requires a hit on the sweet spot to be valid, I doubt its possible to infer smash of a poor strike with any measured numbers.

[Jon]

Clevited, can you share with us your method of reaching a ball park swing speed.

[Clevited]

Sure. The last entry is where you will find the latest version. Its really simple, I just found a relationship like I mentioned above. I back solved it more or less and I really didn't spend a ton of time trying to get it perfect but it is almost always within +-2 mph club speed. It doesn't do well with abnormally hot clubs like fairway woods and hybrids can sometimes be but it still should be close. It also doesn't do great with sand and lob wedges sometimes. But for most clubs it is quite accurate I find, and others have found.

https://golfsimulatorforum.com/forum/skytrak/123602-smash-factor-and-club-speed-calculator

Edit: Just another note, there are a few of us that utilize voice caddies to get real time smash factors and club head speeds. I have found it to be quite accurate as long as you have it directly behind the ball.

[Jon]

Thanks for sharing that info. I actually used to use the sc200. I really liked it but when I decided to get a skytrak, I didn't think I would have a need for it anymore so I sold it. I also found it to be fairly accurate from gap wedge through 4 iron. In my experience with voice caddy, anything under 90 yards was inaccurate(as far as yardages go). That is something I really like about the ST. You can hit 50 yard shots with a lob wedge that will register legit carry distances in the ST app.

[Clevited]

No problem. Yeah, I don't pay any attention to the carry distance it shows, just club speed, ball speed and smash factor. It helps me verify any Skytrak misreads (I have had 205 mph ball speed on occasion, NOT possible!), and see my club speed. Also helps me verify my calculator.

[Morini]

Clubhead speed is quite consistent swing to swing (usually within 2 mph), and changes little day to day, or even week to week. As such 95%+ of change in ball speed is caused by contact. Since one can't get better than optimal contact, and smash factor pretty well peaks at 1.5, simply identify your best drives (long carry, straight, low side spin, fast ball speed). Then take that ball speed and divide by 1.5 (perhaps slightly less), and you will have a very good estimate of your club head speed.

For other clubs you can use the LPGA/PGA smash factors from here:

[Clevited]

I would tend to disagree with this based on personal experience and from what I see from pros. Clubhead speed can change quite a lot day to day. I have days where I just don't feel strong and drop almost 10 mph. Monte Scheinblum has a video where he mentions that there are days when he is much slower, I have seen plenty of pros ball speed numbers that are substantially lower day to day swing to swing according to Trackman.

Smash can also for the average joe, vary wildly for sweet spot strikes on almost all clubs. You flip that club through impact, there goes your pga smash factor comparison. To learn if one is maximizing what they can get out of each club, smash factor is useful to know and compare to what the pros are doing. It has helped me at least ferret out my EA flipping problem.

To summarize, I think knowing clubspeed and therefore smash factor is very important so its useful to have a means of accurately measuring it.

Edit: I do agree that contact is like 95 percent of the problem, but swing speed can vary quite a lot especially for high handicappers.

[skytrakali]

Yes - I agree with Morini. When I've measured my club head speed (using something other than ST) it's been REALLY surprisingly constant. I hit it "really fast" and then "really slow" (I think) but actually the change is very little. So I agree with Jon that smash factor may be interesting, but for me I can tell far more by how it feels off the club and how far the ball goes etc. Also, "real" smash factor results are very closely grouped. So that's why I don't find it that helpful.

[Morini]

I guess we are all different, but over thousands of measured swings that i have seen by myself and others, the vast vast majority are in that 2 mph window. Similar to what ali mentioned, if i swing out of my shoes and then take some off for an easy swing, maybe 5,6 or 7 difference. 10 mph day to day change would be extremely rare, and those who are in this predicament have far bigger things to worry about than skytrak calculated chs.

The skytrak will never achieve accurate per swing chs. I'd complement with skypro and/or swing speed radar and/or yupitero.

On the topic of skypro, i have great hopes for integration with skytrak. It will give us accurate smash for sure, but I have a hunch that it will give us much more than that. I am hoping for path and even face angle. I am not sure if Gord Parke is still involved with skypro ( he was one of the original developers), but i hope he is. He us a very smart and resourceful guy, and i know he has been testing additional skypro metrics, but couldn't get the accuracy that he needed. With skytrak integration, this should a snap, and could take us into consumer launch monitor territory.

[Clevited]

I guess I was referring to a full rip with a driver. Not a slowed down control swing. You can easily see a full rip with a driver vary quite a lot just by looking at pga clubhead speed stats. There is a wide range between max and mins. One could say they slow it down for some swings and that could be the case for some tour players but a lot of them are giving it full rips but those rips can vary significantly day to day. That combined with what i know about myself and what Monte has said, and what I see from videos of tour players and non tour players, i came to the 10 mph conclusion.

If you don't have that large of a drop in speed ever, that is a really great talent and a blessing in my mind.

Edit: Just to clarify, up to 10 mph is what i ever expect one can vary if not injured or something. 5-7 is what I would expect to be common day to day.

[Jon]

Integrating various teaching aids with the ST has certainly been useful for me since purchasing the ST less than a month ago. I frequently use swingbyte for swing plane and I'm sure I could find some use of a device that accurately tells you the degrees your face is open or closed at impact. I've heard that r-motion does this to some extent. I'm all for getting as much quality data as possible. I think it would be t6hat much better if that extra data was able to effect the ST ball flight simulation. From the sound of Morini's comments above, maybe sky pro integration is in the works for ST. I checked out the sky pro site. I didn't find the sky pro swing sensor to be anything that a dozen companies aren't doing better for a fraction of the cost, but maybe I'm not seeing the full picture. Integrating club data into the ST ball flight simulation would certainly qualify as different and separate it from the pack of swing sensor units available today. Does anyone here know anything about what is in the works for ST integration with sky pro or other products.

[Morini]

I believe that seth has confirmed that skypro integration is in testing and will come. At very minimum, it would simply be a combined app. But given the amount of time that has passed, they are hopefully looking at some synergies that will allow for new club data metrics.

If they are able to get reasonably accurate face & path, it could serve as a poor man's Trackman alternative. Is there a market for this?

[Jon]

I believe there is. Anything that improves the results of the skytrak would be a worthy purchase

[Morini]

I don't think it will do much of anything for ball flight numbers. It is theoretically conceivable that adding skypro data could provide a small improvement in horizontal launch angle, which happens to be ST's greatest weakness.But it would be so small that it wouldnt be worth the effort.

The benefit would be additional clubdata, such as "measured" clubhead speed, thus accurate smash.