Thursday, 4 May 2017

Chrome Soft vs Chrome Soft X

Introduction
I love the Callaway Chrome Soft, without doubt my favourite ball. The introduction of an X version meant I had to test it.

Hypothesis
This is an interesting one. My previous testing with premium balls and indeed other comparisons between these models suggests there will be no difference. However, Callaway claim the X version should fly lower and spin slightly more whilst feeling slightly firmer.

A excellent review here.
GolfWRX review here.

Method
Within the limitations of my indoor setup I tested by capturing 5 solid shots (not blatant mishits) with both balls and multiple clubs. Shots were struck from a soft range mat. Using this mat I have noticed shots launch higher and travel less distance compared to a firmer mat or turf. Spin rates are also significantly higher and less variable than those encountered playing 'real' golf.

The balls were:
Callaway Chrome Soft
Callaway Chrome Soft X

The clubs were:
LW (60°) (goal was a 36 yard pitch)
SW (52°) (goal was a 90 yard pitch)
6 Iron (29°)
3 Iron (21°)
3 Hybrid (21°)
2 Hybrid (18°)

Results and Analysis

Subjective:
The X ball is superb/weird. It felt very similar-slightly firmer to me but made a noticeable click compared to the duller thud of the normal chrome soft. I really like the click and soft feel of the X, but I also really like the thud and soft feel of the normal ball!

Data:
These are screenshots, the first club is the normal chrome soft, the second is the X.


As usual, raw data can be found here.

Does the X fly lower?
Not the way I hit it!

Does it spin more?
Technically I think it might a little; with the exception of the 36 yard pitch every single club did spin slightly more. However, I dont think a few hundred rpm of additional spin is going to affect my scores!

Conclusion
I think this was as expected. There may be differences between these balls if you are a tour player but as an amateur a premium ball is a premium ball. I would and will happily play either chrome soft model.

Next Steps
Once I get a setup capable of withstanding 3W/Driver shots repeat the testing.

Tuesday, 21 March 2017

Efficiency & Spin Axis

As someone who finds the maths and physics of Golf almost as interesting as playing I read and watch a lot in an attempt to improve my understanding. This led me to dig a bit deeper into my driver data, specifically efficiency and spin axis.

ST does not measure clubspeed it is calculated (with good accuracy). It measures ball speed with high accuracy. I therefore extracted my data and calculated bsCarryEfficiency, bsTotalEfficiency, csCarryEfficiency and csTotalEfficiency.

The PGA tour measures carry and total efficiency comparing clubspeed to carry and total distance.
For carry efficiency the 2017 range is 1.918-2.616, my average across my ST data is 2.4
For total efficiency the 2017 range is 2.391-2.936, my average across my ST data is 2.63
Fig 1
Figure 1 shows my bsCarryEfficiency distribution. The mean is 1.64, Q1 is < 1.6 and Q4 is > 1.69. It therefore seems reasonable to conclude anything at or above 1.69 is an efficient drive.

Having watched numerous youtube videos of various professionals I noticed a number of them were posting driver data with significantly greater carry distances than myself despite a similar or lower ballspeed. Spin rates and launch angle were similar so the distances should have been comparable. I therefore looked at other launch parameters and once again found myself looking into Spin Axis:
Fig 2
Figure 2 compares spin axis with ball speed carry efficiency for my driver data. PGA tour style carry efficiency would be better but I didnt want to rely on a calculation and using ball speed reduces (not eliminates) the effect of strike on the data. Within this data there is a curve (albeit with a low r2 value of .3397); increasing spin axis (left or right) generally reduces efficiency which makes sense. Using this data an efficienct drive requires a spin axis of +- 20deg (+-700rpm of side spin). My normal dynamic loft is 15.5deg so I need the face and path to be within 4.5deg of each other to hit an efficient drive (data taken from trackman university). The low r2 value will be the effect of strike and delivery, so you can have a low efficiency straight drive but you cant have a high efficiency crooked one (from the perspective of carry).

Skytrak, Trackman, GC2/GCQ
Going back to my youtube comment I decided to add some extra data; I added my trackman data from my recent Skytrak vs Trackman test, and manually captured data from youtube to see how the data compared. All of this data was produced on GC2/GCQ from various pros and also some amateurs:
Fig 3
Figure 3 shows the bsCarryEfficiency for Skytrak, Trackman and GC2/GCQ. Trackman shows a wider range which makes sense, it is measuring actual ball flight and there are lots of variables at play (open data). However, I think the GC2/GCQ data proves my observation that the youtube carry distances posted are significantly higher than ST and Trackman. This means for every mph of ball speed you put in a GC2/GCQ will likely calculate a more generous carry distance than a ST or a TM would observe.

Returning to Spin Axis
I then decided to reproduce the spin axis chart with the additional data and see how it compares:
Fig 4

Figure 4 shows the efficiency vs spin axis plot for the 3 data sets and I this this illustrates a few things:
1. The TM efficiency data is comparable to ST except the spin axis values are generally smaller. This was already noted in previous testing.
2. The range of spin axis measurements for ST and GC2/GCQ are comparable (more extreme than TM) so perhaps the ST isn't exaggerated compared to GC2/GCQ? Much more data would be required to prove this.
3. The GC2/GCQ is significantly more generous in its carry calculation, to the tune of 10 yards at my average ball speed of 155mph.

Thursday, 9 March 2017

Flightscope Trajectory Optimizer - Launch Angle

http://flightscope.com/products/trajectory-optimizer/

This is a great tool and I use it frequently to assess my launch conditions against a different flight model (Flightscope instead of Skytrak or Trackman), and also to experiment with different parameters so I can analyse how they affect distance.

I launch my driver quite high, on average between 14.5-16 degrees. Trackman suggests the optimum for my ball speed is closer to 13 degrees so I wanted to assess the impact and it turns out the results are quite interesting.


The coloured columns are carry, total (hard), total (soft).
This suggests high launch is not a big issue, and strongly indicates it is better to err on the side of launching too high vs too low. According to this launching at 17deg is optimum for carry, but even launching at 25deg will only cost you 6.5 yards of carry and approx 10 yards of total distance in hard conditions. Conversely reducing launch angle to 9 degrees will cost you 10 yards of carry. From this point carry distance drops rapidly with decreasing launch.

N.B. the dip in the curve for total (hard) at 10 degrees launch.

133mph ball speed
I thought it might be interesting to compare this with a lower ball speed (the average ball speed of player a from our Skytrak vs Trackman test).

A similar pattern emerges and optimum launch increases to a whopping 20-22deg. How many amateurs launch their driver at 20-22deg???

The dip in the curve for 10deg launch is much more pronounced. Not sure what this indicates???

Friday, 3 March 2017

Skytrak vs Trackman Pt 2 - Shot by shot Player A

Introduction
After the first part I wanted to try and illustrate the data captured on a more blow by blow basis so this is that attempt; this will therefore be a very chart heavy! Each chart shows the Skytrak and Trackman data, aligned shot by shot.

This is the actual Trackman data with no normalisation. Differences in calculations from the ST flight model should therefore be expected (but I still expect it to follow the measured data (e.g. short shot = short shot etc).

Summary data is useful but I think the below shot by shot charts illustrate just how accurate the ST is.

Ball Speed

I think this is highly impressive and shows excellent correlation between both systems. The difference is normally negligible peaking at approx 7.7mph in the worst case.

Club Speed
As a calculated parameter this is surprisingly close to the measured Trackman value.


Vertical Launch


Horizontal Launch


I think this shows the subtle difference in alignment between the 2 units. If you subtract approx 1.5 deg (turn the ST 1.5deg left) they match even more closely. I do not believe these 1.5deg affect the spin axis measurement but they do affect the offline projection.

Total Spin

I think this is the most impressive chart of all, Skytrak can measure spin rate with phenomenal accuracy. It is this which makes me think the Spin axis deduction is not calculating as expect (as opposed to capture). The sizeable deviations are caused by Trackman not returning total spin.

Spin Axis

As previously noted this is the only troublesome measured parameter. I think this chart clearly shows the Skytrak is measuring Spin axis (I would even say accurately) but for this player it is predominantly skewed in a negative direction. For myself (Player B) I am pretty sure we will see the reverse (skewed positively) because our shot shapes are opposing.

Flight Duration

A calculated parameter for Skytrak. This is impressively close considering we were hitting range balls with a slightly reduced distance.

Descent Angle
A calculated parameter for Skytrak, impressively close to Trackman for the majority of shots.

Peak Height

A calculated parameter for Skytrak, impressively close to Trackman for the majority of shots.

Smash Factor

A calculation based on a calculation so potentially risky. However, it seems impressively close to the Trackman value. 

Offline


As previously noted the wind was slightly helping and from the right. You would therefore expect the ST shots to finish right of the actual TM shots? However, if you take into account the circa 1.5deg alignment difference between the units (ST alignment approx 1.5deg right of TM target) I think these are almost identical.

Carry Distance

Carry distance looks spot on considering they were range balls.

Total Distance

As before total distance also tracks as you would expect (for a range ball).

Skytrak vs Trackman Part 1

I recently conducted some testing to compare my Skytrak to Trackman. I have read a number of comparisons (mainly by golf magazines etc) but none of them come across as very rigorous and they didn't share complete data so that others can peer review/scrutinise.

The objective of this testing was simple, assess the accuracy of my Skytrak against the industry standard Trackman and present full results so others could peer review.

Method
Myself and a playing partner hit balls with a variety of clubs collecting the raw data from both systems.
The balls were range balls (I will cover this later), but they were high quality srixon range balls. In Trackman ball conversion terms they are the equivalent of hard (reduced spin with short irons, elevated spin with long irons/woods).
The weather was excellent (for Scotland in Feb!), approx 6C with a light wind helping slightly from the right.
Skytrak software version was 2.5.4 on and Ipad Air 2.
Trackman 3 in Outdoor mode.

Results (Player A)
Source Data Link



These are the results averaged across all shots and shows excellent correlation across the data except spin axis/side spin. This leads to reduced accuracy for the offline figure. However, I think it is important to remember this is range ball data hitting outside so this is comparing what actually happened to the ball vs the Skytrak flight model. 

Initial Thoughts
  • My Skytrak behaved impeccably throughout this test. Trackman missed 1 shot whilst we were setting up, and Skytrak missed 2 shots during this test. I think this was down to my playing partner hitting the followup ball too quickly.
  • Trackman frequently missed spin data (you can see some of this in the detail worksheet). Skytrak did not miss once, and the results match so closely I found myself trusting the Skytrak data over the Trackman (The trackman spin numbers appeared to fluctuate more).
  • Some people have complained about the delay on Skytrak. For plenty of the longer shots we found ourself waiting for Trackman to finish tracking the ball and present its full data rather than the Skytrak!

Horizontal Launch
This was one measurement I expected to vary because of differential alignment between the systems. Despite this I believe the Skytrak data is very accurate and consistent. The spec for Skytrak is 2Deg and it was within this tolerance.

Spin Axis
The spin axis seems to be exaggerated frequently leading to excessive curvature on shots. My initial response on witnessing this was the Skytrak struggling to read/calculate the side-spin component accurately.  However, given the accuracy of the total spin (or backspin component) and horizontal launch angle it seems highly improbable the raw data capture was to blame. It therefore seems likely there is something weird in the way that raw data is converted into spin axis.

I raised this issue with support and was advised to reinstall the Skytrak software which I have done. At some point I will need to retest and see if the spin axis is captured more accurately.

Conclusion
With the exception of the Spin axis phenomenon described above I was surprised by how closely my Skytrak matched the Trackman data. I think the important parameters (ball speed, v-launch, h-launch, total spin) were measured with highly impressive accuracy especially when you consider the cost differential (2k vs 25k) and the fundamentally different ways in which these units operate.

I will also say that I couldn't use a Trackman at home due to its space requirements, but if I wanted an outdoor ball tracking device and cost wasn't a factor I would definitely have one. The Trackman software is phenomenal and the amount of data it captures with unerring accuracy is amazing. When conditions allow there is no substitute for measuring what actually happened vs what should have (even though the latter is very accurate!). It is the benchmark.


Next Steps

  • Try to summarise across all clubs, shot by shot.
  • Player B data.
  • Open pandora's box and delve into some of the raw Trackman data!
  • Experiment with normalisation and see how that affects the data!
  • Examine some individual shots.
  • Find a GC2/GCQ to test against!


Thursday, 16 February 2017

Skytrak Skills Assessment vs Trackman Combine

Tracking shots is great and provides a wealth of data. However, the Trackman Combine test makes you focus on a target and puts you under pressure. I think it is a brilliant practise aid so the ability to complete something similar on Skytrak was a significant factor for me before I purchased it.

Having completed several Trackman Combine tests and plenty of Skytrak SA (Skills Assessment) I thought it would be interesting to see how they compare.

Trackman presents you with various targets (60, 70, 80, 90, 100, 120, 140, 160, 180, Drive). All targets are based on carry distance and based on proximity to the target you are given a score out of 100. They than map the score to a handicap based on real data collected from people completing the combine test.
http://blog.trackmangolf.com/performance-of-the-average-male-amateur/
http://mytrackman.com/media/5df25dca-3bc5-41b5-bca8-c3badebdd3b7/content/5_
https://mytrackman.com/media/9e613e61-a366-49cf-8b6f-26c9809c1fc9/CWsVnw/PDF/1.%20TrackMan%20Golf/2.%20Combine/TrackMan-Combine-brochure.pdf

Trackman does not show the calculated handicap for an individual shot.

Skytrak SA is similar although the distances are based on Total Distance as opposed to carry. If you are using Premium balls and hit the ball consistently your spin rate will be high enough for the difference to be negligible (the ball will stop dead or spin back slightly on the Skytrak Green). Each shot is assigned a dynamic handicap based on proximity to the target.

Having completed 3 combine tests and numerous SA's it is immediately apparent the SA is way more punishing for my ability. My combine scores have ranged between 70-78 which places my Trackman handicap between 0-4. My SA scores have placed me between 5-13.

I therefore set about comparing proximity to calculated handicap to see what patterns emerge:









Some very clear patterns emerge:

  • Skytrak uses a linear equation to calculate handicap from proximity to target.
  • Trackman uses a quadratic equation to calculate handicap from proximity to target.
  • Skytrak and Trackman roughly agree in the 18-20 handicap range.
  • Below 18 Skytrak becomes increasingly punishing compared to Trackman.
  • Above 20 Skytrak becomes increasingly lenient compared to Trackman.

The following chart compares proximity to handicap at varying distances.
From this it becomes even clearer how punishing Skytrak is to better scores. A male scratch golfer will on average score 72 on trackman. He will score a dynamic handicap of approx 8-9 on Skytrak! Because the handicaps converge in the 18-20 region it seems logical the handicap region between 8 and 20 is compressed on Skytrak compared to Trackman (12 handicap units vs 20). This means a 1 shot improvement between 8-20 equates to a real world improvement >1 shot. It also means attaining a 1 shot improvement <8 Sh Hcap becomes exponentially harder compared to Trackman and thusly real life. The Sh Hcap is still in beta (as of 2.5.4) so in my opinion it seems sensible to adjust the algorithm to take this into account.

Conversion
Using this data and excel it is possible to ascertain conversion equations between the systems:
Th - Trackman Handicap
Ts - Trackman Score
Sh - Skytrak Handicap

Trackman Handicap from Trackman Score
Th = -0.0052Ts2 - 0.1572Ts + 38.226 (r2=0.9952)

Skytrak Handicap from Trackman Handicap
Sh = 0.0077Th2 + 0.4029Th + 8.5378 (r2=0.995)

Trackman Handicap from Skytrak Handicap
Th = -0.0254Sh2 + 2.5073Sh - 19.453 (r2=0.9932)



Tuesday, 31 January 2017

Wet Ball Testing

Update 06/02/17:
I would love somebody to peer review/verify my results...

Having had my Skytrak for a few weeks I have noticed a strange phenomenon when practising at the driving range which I also observed last year on Trackman:
During my Trackman practise I would sometimes observe significant distance differences from one session to another. At the time I thought it might be local weather conditions; a strong headwind reducing distances some days and not others. During each session the wind didnt feel overly strong but distances varied significantly.
My first range session with my skytrak produced a similar distance deviation; I was hitting short-middle irons approx 1-2 clubs longer than normal. When I started looking at the data it became clear the spin rate was significantly lower than expected, not higher as I have typically found with range balls. At the time my teaching pro said it was probably because the balls were wet but I didnt appreciate the difference it made so I set about testing this.

Please see my previous post for the dry ball data here.

Research
This seems to be a poorly studied area with relatively little information available:
http://blog.tourspecgolf.com/wet-versus-dry-golf/
http://www.andrewricegolf.com/andrew-rice-golf/2013/02/wedges-and-water
http://blog.trackmangolf.com/the-difference-in-range-ball-distances/


Hypothesis (largely taken from dry ball testing)
Spin rate will be reduced. Spin rate will be higher with premium balls and lofted clubs.
Distance is largely the same across different ball types but it will be higher when the ball is wet due to reduced spin.

Method

Within the limitations of my indoor setup I tested by capturing 5 solid shots (not blatant mishits) with 4 balls and three clubs. Shots were struck from a soft range mat. Using this mat I have noticed shots launch higher and travel less distance compared to a firmer mat or turf. I dropped each ball into a pot of water prior to hitting.

The 4 balls were:
Titleist Pro V1x
Callaway Chrome Soft
Titleist DT Trusoft
Callaway Supersoft

The clubs were:
PW (46.5°)
7 Iron (33°)
5 Iron (26°)


Results and Analysis

The results shocked me:

A 74% reduction in spin rate between premium and non-premium ball with a PW.

A 21% increase in carry distance (31 yards) between premium and non-premium ball with a 7 iron.




I was expecting to see a difference, but not of this magnitude. That is almost 3 clubs of difference with a 7 iron, not to mention the additional rollout you would get on landing (42 yards in my Skytrak data).

This analysis took several attempts to capture because the quantity of water needed to decimate spin was miniscule. When I first ran the testing I tried to do 1 ball at a time, running dry then wet testing with each ball. I started with 2 premium balls so all was fine and results were inline with expectation. However, I couldn't get dry ball results from the two non-premium balls because there was water on my hitting area (the castoff water) which led to a film of water on the club and low spin flyers. I continued hitting for some time (30-40 shots) but it was never dry enough to replicate proper dry results.

Conclusion

  • If you hit the ball reasonably well and play in anything other than a desert use a premium ball. If you dont you risk hitting flyers frequently (even from the fairway).
  • A tiny amount of water interacting with a non-premium ball can decimate spin.
  • A premium ball is largely immune to this phenomenon; presumably because of the softer cover material which allows the grooves to bite.
  • The difference seems greatest with a medium iron.


Supporting Data