Optimizing a Driver's Launch Parameters

Fitting a driver

1. Find the shaft and head combination that the golfer hits the best. "Hits the best" means things like:
• Highest ball speed.
• Best consistency of impact on the sweet spot.
• Consistently good swing path and clubface angle (open/closed).
• Good subjective feel.
Notice that I haven't said a thing yet about loft. As long as the loft is vaguely in the ball park for the golfer, you can fit the other things. They are much more important to driver success than tweaking the spin.
2. Now try out the combination with a variety of lofts. If you have interchangeable heads of the model you're going to use, that's obviously a big advantage. The goal here is:
• Longest distance, as measured by the launch monitor -- or even by eye on the range, if your range is well enough marked to do it accurately. This is most likely to give the best result.
• If you don't have interchangeable heads, you may have to choose a loft "by table". See how the golfer's loft compares with his/her launch angle (for this you'll have to measure the launch angle), and extrapolate to the optimum launch angle in one of the common tables. There are lots of such tables around; I just whipped up the following one, which is as good as any.

  Ball speed (mph)	100	115	130	145	160	175	190
  Best launch angle	17º	15º	13º	11º	10º	8.5º	7º

  Be sure you do this with at least the same model head and the same model and flex of shaft. For flex, you should take measurements and not just rely on the LARSX markings.
3. Optimize launch angle and spin. On second thought, don't bother! You are not going to get more than one extra yard out of this step -- two at the most -- if you did #1 and #2 right.

By the numbers

Note: The calculations in this study were done using the TrajectoWare Drive program, version 1.0. This program provides carry distance only, so that is what is being optimized here. As a practical matter, ground conditions vary so much that it is hard to optimize for total distance (carry + roll) with any great precision -- but we are working on a way to include it in the next version of the program. My rough and ready approach is to use about a degree less loft than the optimum, to reduce the spin and angle of descent.

It's a little hard to understand the shape of this space just looking at a sea of numbers. So let's enhance it graphically. Here is a 3D picture of the yardage contour. The shape looks as if you had taken a paper rectangle and curled it along the diagonal. There is a top diagonal line going from the high-spin, low-launch corner to the low-spin, high-launch corner. The two corners bent down are high launch and spin, and low launch and spin. The whole paper is tilted along the diagonal, so the highest corner is at high launch low spin. At first glance this does seem to say, "Go for high launch, go for low spin". But a closer look (below) is going to tell us to be somewhere on that high diagonal. We will see that moving off the diagonal, even if it is for higher launch or lower spin, is going to cost distance. So going for high launch and low spin helps only if both are added, and in the proper proportions to stay on the diagonal. This 3D graph shows us what is going on very intuitively. But we'll need another way of looking at the surface to get enough detail to understand in enough detail to be useful.

• There is a "ridge" of maximum distance. Here's the same table with the ridge shown explicitly. It is the black dotted line, which is the maximum distance for a given launch angle.
• If you move along the line, the yardage changes rather slowly. If you move away from the line, you lose yardage more quickly. That's what makes it a ridge.
• The ridge is slanted compared to the east-west and north-south axes of the map. It goes from high-launch/low-spin to low-launch/high-spin.
• There is no "peak" on the chart. As you move down and to the right, the distance continues to increase -- but the increase slows to a crawl at the bottom right. (A bit more exploring with TrajectoWare Drive shows a maximum just under 210 yards, at a launch angle of 30° and a spin of 1000rpm.)

• As long as your launch angle and spin are "on the ridge", you are fairly close to the maximum distance you can get with your swing.
• If you do something to reduce (or, for that matter, increase) the spin, you must do something to also change the launch angle, or you will fall off the ridge -- that is, lose distance. Just lowering the spin by itself with not help and will probably hurt. You have change both to stay on the ridge.
• If you just raise the launch angle things, are a little better -- but not much. You may get a slight increase for a few degrees, before the distance goes down again.

Loft	Distance	Launch Angle	Spin
8	149	7.5	1900
10	170	9	2400
12	183	10.5	2800
14	188	12	3300
15	189	12.8	3550
16	188	13.5	3800
18	181	15	4200
20	171	16.5	4700

• 86mph clubhead speed (because 85mph is not enough to keep the ball speed at 124mph, at the loft we are going to need).
• 200 gram head weight.
• Zero angle of attack; the club is at the bottom of the swing at impact.
• The loft listed is the "dynamic" loft, defined at the difference between the direction the clubface is pointing and the clubhead is moving at impact. That means it includes not only the loft built into the driver but also:
• Shaft bend, tilting the head up at impact.
• Face roll, providing more loft as the impact point is higher on the clubface.
• Cupped or bowed left wrist at impact, to the extent that this provides loft and not angle of attack.
• No increase nor decrease of spin due to vertical gear effect. (Here are links for an explanation of gear effect and vertical gear effect.)
• Very normal conditions otherwise: a ball fitting the TrajectoWare Drive model, normal temperature, altitude at sea level, etc.

• Varying loft does not takes us along the ridge; it takes us almost perpendicular to it, straight across the ridge. That means that there is a fairly well-defined optimum loft. In the case of our golfer, the maximum is at 12.8º of launch angle (corresponding to 15º of loft).
• Not surprisingly, the maximum distance occurs where the red line meets the ridge (the black line). That's not surprising because the ridge represents the best spin for a given launch angle, or the best launch angle for a given spin.
• The maximum distance -- the intersection between the black and red lines -- is a long way in launch space from the maximum distance possible. It misses the peak (of 209.7 yards) by 17º worth of launch angle and 2500rpm worth of spin. 
• If we could somehow traverse this distance of launch angle and spin, there is about 20 yards to gain -- about 10% of the distance of the drive. That is a lot, if we could somehow obtain it. (But, as we shall see, this is not easy. Moreover, it has less to do with club design and more to do with the golfer's swing.)

Fine tuning

Loft

• First the good news: loft increases launch angle by almost a degree for every degree of loft. (Actually, it is not quite one-for-one, more like 80%-90%.)
• Now the bad news: loft also increases the spin. For our 86mph golfer with typical driver lofts, the spin increases by 270rpm for each degree of increased launch angle.

Angle of attack

• Long drive data: These guys have a lot of athletic ability, plus a strong motive to learn an upwards angle of attack; they need both in order to compete. So we can look at the actual data from the high finishers in elite long drive competition and get an idea of the AoA that they manage. I plugged the launch data from two drives from the 2006 ReMax finals into TrajectoWare (they were drives Jason Zuback and Erik Lastowka), and worked backwards to the loft and angle of attack that they must have used. In both cases, the angle of attack was under 1º. I was surprised it was so small.
• More long drive data: Tom Wishon points out that "the long drive competitors can use a head with 5-6 degs and still generate a launch angle of 11-12 degs." Even allowing for a reasonable shaft bend increasing the loft by 3º, this is still 3 or 4 degrees of upwards angle of attack.
• Geometry: If you can somehow tee up the ball 6" farther forward in your stance, the natural arc of a 45" driver will allow hitting up on the ball by an angle of 8º. That is a lot. It will also involve teeing the ball up almost a half inch higher. This is probably an extreme upper limit to angle of attack, nowhere near available to most of us.

Vertical gear effect

• Tom Wishon has reported a difference of 425rpm for a 1/2" vertical difference of impact position on the clubface, with a 105mph clubhead speed. A difference of 1.5" from a very low on-face hit to a very high on-face hit allows 3/4" from a center hit to a high hit. With Wishon's numbers, that allows a little over 600rpm to be saved by vertical gear effect.
• Dana Upshaw has reported a difference of 3300rpm between a high-face hit and a low-face hit, corresponding to a difference of 1650rpm from a center hit to a high hit. That is almost 3 times Wishon's data. Upshaw's data was at a ball speed of about 145mph, corresponding to a clubhead speed of 98mph, making the difference even more surprising.

• The golfer must have a repeatable impact high on the clubface. High enough to get maximum benefit from the gear effect, but still low enough not to lose COR.
• The golfer can be helped a little by a low center of gravity for the clubhead. A low CG increases the range and efficacy of hitting "above the center".
• Shaft flex! (Finally, something we clubmakers can relate to easily.) Upshaw has reported an anecdote involving a long drive champion getting much better runout after landing after going to a flexible-tip shaft (generally considered high-launch and high-spin) and a lower loft in the clubhead. The explanation Dana gives is that the clubhead was more free to rotate and exercise vertical gear effect with the tip-flexible shaft -- and I concur.

Other factors?

• Head weight distribution - A low center of gravity is reputed to give a high launch angle without adding spin. Vertical gear effect is a technical explanation for why that should be. A low CG enhances the vertical gear effect as noted above.
  Oh yeah. There's also the possibility of raising the launch angle by moving the center of gravity back away from the face. That definitely works to raise the launch angle. But it has the same effect as loft -- increasing the spin as well -- so it's not helpful this time.
• Shaft flex - Stiff shafts, and especially tip-stiff shafts, have a reputation for being low spin. (Also low launch. That is not what we want right now, but remember that because it's important.) The biggest launch effect of shaft flex is on the dynamic loft of the clubface. So if you reduce spin, you also reduce the launch angle. The only valid use of shaft flex to reduce spin without lowering launch is as Dana Upshaw revealed; use a tip-flexible shaft in conjunction with a lower loft clubhead to take maximum advantage of gear effect. The shaft flex will increase the loft, the lower-loft clubhead will get the loft back down, and a high-face hit might get less backspin because the shaft will allow more clubhead rotation and the resulting gear effect. (I qualify it with "might", not "will". My analysis does not support the substantial effect that Upshaw noted. So I accept his data with considerable reservation.)
• Low-spin face - I don't know of a single instance of face design or face treatment that reduces spin. (At least none that is legal. Adding some sort of of slime when you play is not legal.)

Tuning up

• Loft moves across the ridge. Wrong direction.
• Angle of attack is either there in the golfer's swing or it isn't. If it is, we already accounted for it in step #2.
• Vertical gear effect is all that is left. Let's look closer.

1. Use impact tape or powder to determine ball impact. If impact is scattered, don't even to try to tune any further; this golfer needs lessons and practice, or at least attention to the gross driver fitting (step #1) that would give consistent high-face impact. Continue only if the impact is "tight".
2. Find the proper tee height for high impact that still retains full ball speed. This will take a launch monitor and impact tape or powder.
3. Experiment with shafts to find the one that gives the greatest spin reduction for the ideal impact. We're still monitoring impact here. Don't draw conclusions based on lower or higher impact. That will "churn" your shaft selection. If you can't get stable enough impact for this step, stop trying to fit for vertical gear effect.
4. Now that the spin is lower, we have to get back to the ridge of maximum distance by adjusting the launch angle. We use loft to do this. We may need to decrease loft; that's a good thing, because it also decreases spin. Or it may be increased loft, in which case we have to spend some of our spin reduction to get back to the ridge.

Long drive!

1. Loft? No, that won't work. As we see from the purple line, it moves us across the ridge, not along the ridge.
2. Shaft profile? Probably won't help. Any change of launch angle due to changing the shaft is a combination of "spinless" (which works like a change in angle of attack) and "spin-inducing" (which works like a change of loft). Unfortunately, over 90% of the contribution to launch angle is spin-inducing. So it mostly works like loft, which is not helpful in moving us along the ridge.
3. Head weight distribution? I have heard that lowering center of gravity of the head will raise the launch angle. I'm prepared to believe this, and even to believe that it does it without adding spin. But I'm not certain that it works; I don't understand it in terms of the physics involved. Anyway, if it does, you can be pretty sure the manufacturers are already building most driver heads this way. So I'll assume there isn't much to be gleaned from this.
   Oh, yeah. There's also the possible of raising the launch angle by moving the center of gravity back away from the face. That definitely works to raise the launch angle. But it has the same effect as loft, so it's not helpful this time.
4. Low-spin face. I understand that some of the multiple-face drivers on the market (like the KZG Gemini) put a lower spin on the ball for the same launch angle. This has been demonstrated and measured. So it's a tool you can use. If you use it, you probably ought to start with it in step #1, not save it for the final tuning.
5. Higher angle of attack! This is not a club design issue, but a golfer-training issue. It requires learning how to hit the ball on the upswing, which implies placing it further forward in the stance and teeing it higher. It works because you can increase the launch angle without increasing loft.
• If you have a 4º increase in angle of attack, you get a 4º increase in launch angle without adding any spin.
• If you go for a 5º angle of attack and a 1.5º reduction of loft, you'll get exactly what we're looking for: a 4º increase in launch angle and a 500rpm reduction of spin.

Summary

1. Begin by finding the length, shaft, and clubhead that the golfer hits consistently at high ball speed. Use a loft within 2-3º of what the golfer needs, but don't worry too much about loft now -- just consistency, ball speed, and comfort.
2. Now vary the loft, using these components, to give the maximum distance for the golfer.
3. You are now within 10 yards -- 15 at the most -- of what is "on the table" for that golfer's swing. You might be able to make small changes in distance using a launch monitor and different shafts. Bigger improvement can be made if you can get the golfer to hit the ball consistently high on the clubface.

Acknowledgements

Hi, Dave! Have you ever looked into ideal launch angles and spin rates based on ball speed? I do a lot of Vector fittings (with good results, I might add), but wondered if you'd ever taken any interest in the subject.

I have never played with shafts or weight distribution trying to change the spin at a given launch angle. From what I have seen, the strategy should be:

• Find the shaft and head style that the golfer seems to hit well and feel good with.
• Run lofts for that head and shaft, to find the optimum loft for the golfer. Use only center hit data, determined by impact tape and consistency of the numbers on the LM.
• You will find a pretty broad maximum, with essentially the same distance over a 3-4* loft range. Use a number toward the lower end of that range. Don't worry about exact launch angles or spin at this point; there aren't more than 2-3 yards to be wrung out of it now anyway, and the golfer's consistency (with a head and shaft that feel good and suit his eye) are more important at this point than those last 2-3 yards.

I know that's backwards from what a lot of professional fitters do. They tend to start with a loft that gives the "proper" launch angle, then play with heads and shafts to get closer to the optimum spin for that launch angle.

Dave: I may have argued the importance of spin 6 months ago (which is why I emailed you in the first place), but my findings after many Vector fittings agrees with what your article states completely.  In the past, I'd get great launch/distance results, but would waste additional time with the customer because the spin rates just didn't make sense. Now I know why.

Thanks for your input (as I'm sure many others will also do). Now I can spend a lot less time trying to get loft & spin to match so closely.