Non-conforming driver gains. High COR math!

[Solmors]

This started with me researching drivers and learning about the 0.83 COR max allowed by the USGA and that there are drivers you can buy that are non-conforming due to >0.83 COR. That's when I found a website that charges ~$130 to mill the face of your existing driver to increase the COR. That website made sure to note that by doing it the drivers are no longer legal in competitions or handicapping. They had recommended COR for each swing speed because the thinner the face, the more likely a faster swing is to break it. There are all sorts of claims about "20-40 yards more!" but I never trust the marketing, so I set out to find the math. And here it is:

ballVelocity = (clubHeadVelocity * (1 + COR)) / (1 + (ballWeight / clubHeadWeight))

I have a Mizuno GT180 driver which has a 200g club head and I assume a USGA legal 0.83 COR (likely a little less due to tolerances), all balls are 46g nowadays (I measured a few different brands I had in my bag to be sure), and I swing about 115 mph. So my calculated ball speed is 171.1, which is about what I would expect and see when I get a solid connection.

But what if I had a COR of 0.87 (what the website recommends for 110-120 mph swings)? The ball speed would be 174.8, which is 3.7 mph faster. The usual estimate for carry distance based on ball speed seems to be 1.75, so 3.7 * 1.75 = 6.47. So by getting an illegal head and a good amount of money, I would only be increasing my carry distance by about 6.5 yards. Not worth it IMO.

If anyone is interested here are the calculations for other swing speeds and their recommended COR change.

• 100 mph: 148.8 mph to 153.7 mph at 0.89 COR. +4.9 mph (+3%) and 8.6 yards

• 85 mph: 126.5 mph to 131.3 mph at 0.90 COR. +4.8 mph (+4%) and 8.4 yards

• 70 mph: 104.1 mph to 109.3 mph at 0.92 COR. +5.2 mph (+5%) and 9.1 yards

• 50 mph: 74.4 mph to 78.5 mph at 0.93 COR. +4.1 mph (+6%) and 7.2 yards

So as you can see, as you get down the lower swing speeds the percentage of gain increases. But even at the slowest swing speeds you are only seeing an increase of 6% ball speed. At no speed are you likely to see a even a 10 yard gain, much less 20-40 yards.

What if there was no USGA regulation and R&D money could be put into making a higher COR face that was also durable and could be hit by faster swingers? Lets say a 120 mph swinger was able to hit some state-of-the-art 0.95 COR driver, how fast would the ball speed be (keeping 200g head weight)? Answer: 190.2 mph which is a gain of 11.7 mph from the current 178.5 mph he would get with a 0.83 COR face. His carry distance would increase from 312.4 yards to 332.9 yards, a 20.5 yard increase!

Also of interest, if you are able to increase the weight of the head and not lose speed. For example if I added 10g to my club head (just a 5% increase) and not lose any swing speed, my ball speed would increase to 172.6 which is 2.6 yards of carry. But if I lose even one mph in club head speed that gain is lost. So adding weight to the head is unlikely to help gain you more ball speed (due to the weight alone at least) and could possibly even lower your ball speed.

I'm new to the forum, so I'm not entirely sure this is the correct sub-forum to post this in. If not, let me know. Thanks!

TL;DR: You will likely only see a gain of 5-10 yards by playing a non-conforming driver if you stay within the recommended swing speeds for each COR. If you go over the recommended COR for your swing speed you could possibly see a 20 yard gain if you have a very fast swing, but it is highly likely you will quickly break the face of the club.

Edited November 25, 2020 by 1t2golf
Link to website removed. PM OP for info.

[Stuart_G]

Just a minor side note. 

 

Actual gains will be a little less since the equation you're using is assuming 0* spin loft (no spin imparted to the ball at impact.    Tutelman estimates that by adding an additional multiplier of:   cos(spin loft)   For a driver that would typically be 0.95 to 0.97.

 

 

[Adam C]

If you are looking for more distance, you are better off looking at non-conforming golf balls then club heads since that is where more of the distance gains are coming from.

[Ri_Redneck]

It's not always the case that a heavier head will result in a slower CHS. Depending on the balance that suits the golfer, many can actually increase speed and/or center contact reliability by adding weight to the clubhead. You just have to try things out to see what's best for the golfer.

 

BT

[joostin]

Welcome fellow math calculating wrxer (golf nerd) with similar swing speed.  Good info.  Yeah those face shaved drivers just don't seem worth it for distance claims that are too good to be true.  I'd worry about caving in the face.  Clubhead speed is the biggest factor in ball speed as can be seen just looking at the equation.

 

I'm more impressed that the face shavers can actually machine it accurately.  I'm guessing they map the face in CAD/CAM, then just offset the surface for the ball end mill to follow.  I'd worry more about their fixture setup than the CNC machining itself.  Hopefully its mapped and machined in the same exact setup, so it's not crooked and thin areas get thinner than expected.

[Solmors]

10 hours ago, Stuart_G said:

Just a minor side note. 

 

Actual gains will be a little less since the equation you're using is assuming 0* spin loft (no spin imparted to the ball at impact.    Tutelman estimates that by adding an additional multiplier of:   cos(spin loft)   For a driver that would typically be 0.95 to 0.97.

 

 

Thanks for bringing up Tutelman! I have just been getting more into golf as of this year and have never heard of him before, spent a bunch of time reading through some of his articles. Fascinating stuff! And yes, I am assuming the same launch conditions for before and after other than a higher COR face so you are right, the true numbers will be different (but not significantly so I think).

 

5 hours ago, Adam C said:

If you are looking for more distance, you are better off looking at non-conforming golf balls then club heads since that is where more of the distance gains are coming from.

Are there non-conforming golf balls that have longer distance? The only thing I can think of would be a heavier ball, but that would only be longer for the very fastest of swing speeds and I haven't seen any non-conforming heavy balls for sale anywhere. And even then the distance gained would only be ~10 yards max or so. I'm not really looking for distance that much myself, this research was more for academic and curiosity sake. 

 

4 hours ago, Ri_Redneck said:

It's not always the case that a heavier head will result in a slower CHS. Depending on the balance that suits the golfer, many can actually increase speed and/or center contact reliability by adding weight to the clubhead. You just have to try things out to see what's best for the golfer.

 

BT

That is true, I am sure every person has a unique bell curve shaped CHS to CH weight relationship and where that max speed is will vary from person to person. It would be interesting to take a number of swings at 5 or so different weights and then graph them and then mathematically estimate their max CHS and at what weight that would be. You would need at least one or two weights on both sides of the curve to get an accurate measure, so maybe head weights of 180g, 190g, 210g, 220g, and 230g or something.

 

4 hours ago, joostin said:

Welcome fellow math calculating wrxer (golf nerd) with similar swing speed.  Good info.  Yeah those face shaved drivers just don't seem worth it for distance claims that are too good to be true.  I'd worry about caving in the face.  Clubhead speed is the biggest factor in ball speed as can be seen just looking at the equation.

 

I'm more impressed that the face shavers can actually machine it accurately.  I'm guessing they map the face in CAD/CAM, then just offset the surface for the ball end mill to follow.  I'd worry more about their fixture setup than the CNC machining itself.  Hopefully its mapped and machined in the same exact setup, so it's not crooked and thin areas get thinner than expected.

Yea, I would not trust them with a new driver that's for sure. Way too big of a risk for too little of a return in distance. Not to mention the non-conforming aspect, so if you get caught using it in a competition for handicapping you are screwed.

[pricenicky]

Hi I HAD MY G400 milled by that company last year. Was also using a GD 47 gram shaft at 46 " to get it as light as possibleI hHave had non conforming drivers before.Mine got milled to .890 or so they said.I got about 8 yards increase.Not worth it in my opinion

[Adam C]

Hadn't looked for any ball like this for years but a quick Google search revealed you need to get your hands on the Bandit. Available at Walmart.

 

[Solmors]

17 hours ago, pricenicky said:

Hi I HAD MY G400 milled by that company last year. Was also using a GD 47 gram shaft at 46 " to get it as light as possibleI hHave had non conforming drivers before.Mine got milled to .890 or so they said.I got about 8 yards increase.Not worth it in my opinion

That distance gain is right in line with my calculations for someone with a ~100mph club head speed. I'd agree, not worth it. And don't let any friends test it if they swing real fast!

 

13 hours ago, Adam C said:

Hadn't looked for any ball like this for years but a quick Google search revealed you need to get your hands on the Bandit. Available at Walmart.

 

I did a little poking around on their website and unsurprisingly they give no actual data on WHY they are "illegally long". Their three bullet points are "super reactive core" (so high COR golf ball maybe?), "revolutionary aerodynamic dimple design", and "optimum gram weight" (but don't specify what that weight is). I'm a little tempted to buy a sleeve just so I can weigh and test them. They also carry a non-conforming 0.86-0.87 COR driver with a 488cc head, which is a low COR for a "high COR" driver so I doubt distance gains would be more than 5 yards.