Drivers

1. They are always played off a tee, and
2. They are the only club where maximum distance is THE consideration.

• Since maximum distance is THE consideration, it pays to get lightweight components. Go for the lightest swingweight you can control reliably and, keeping the components light, pad out the length of the club to that swingweight.
• Of course, stick with a club length you can control. If you reach your maximum length of control before you're up to the swingweight you can control, then you can start adding weight back into the components.
• If you need to add weight, weight added in the shaft increases strength and/or torsion resistance, or decreases cost.
• If you need to add weight, weight added to the clubhead increases momentum transferred to the ball at impact (that is, increases distance).
• Where you choose to add weight will affect the balance point of the club. Adding weight in the shaft will raise the balance point, while adding weight in the clubhead will lower the balance point. There is a mostly untested hypothesis around (Monte Doherty's MOI Balance Index -- MBI) that might be restated as: raising the balance point promotes a draw while lowering the balance point promotes a fade.

But doesn't adding length to the shaft put changing requirements on the lie angle of the clubhead? Well, yes. And frankly, few component clubheads have a flat enough lie to accommodate as much as one inch of extra length. I know of none that will handle two inches and still lie properly. Still, the lack of loft of a driver means that lie angle error does not contribute a lot to the simple directional error of the face. That only happens if you scuff the ground before your clubhead gets to the ball. Note that:

• The ball is sitting up on a tee, so the scuff probably won't happen in the area of impact.
• But... for maximum distance, you should be hitting the ball on the upswing. That means that the bottom point of the swing should be several inches behind the ball -- before impact. So an early scuff is a distinct possibility.

For this reason, I like a V-sole or keel sole driver. It is the ultimate in sole "rocker", If you scuff the ground at the bottom of your swing, the contact is directly under the center of gravity even if the lie angle is all wrong. This advantage is not theoretical; I have seen it work for me and for others for whom I've built drivers. A fat hit with a keel-sole driver loses a little distance, but surprisingly little and it still goes straight. Keel soles used to be common in the 1990s (the original Callaway Big Bertha had one, and the feature was widely copied). But driver heads today have twice the size (460cc instead of 230cc), and I don't know of any with keel soles.

Lets look at all the clubhead features that have been sold as driver improvements, and evaluate how much of an improvement they really are:

Jumbo clubheads

The USGA and R&A rules have limited clubhead volume to 460cc. This is much bigger than drivers were in the 1990s when this page was first written. Today, almost all driver heads on the market push the 460cc limit. This increases the peripheral weighting, which does make them more forgiving. They also give more confidence to some golfers, though they are negative images to other golfers. They do have one danger: increasing size without increasing weight results in a weaker structure. No responsible designer would make the clubface substantially weaker, so the sole and especially the big, rounded crown of the clubhead is made weaker instead. The result is increased danger of denting it in handling (not in the normal use of hitting the ball), only cosmetic for most dents, but not all. Another problem with maximum-volume heads is air resistance possibly hurting clubhead speed. Which brings us to...

Aerodynamic clubhead shape

There may be something to this, but I'm a skeptic. Until a rocket scientist (literally) comes along and explains it to me, I'm going to believe that spoilers, turbulators, and airfoil shapes are mostly advertising gimmicks. Mostly, but perhaps not completely. I have done a back-of-the-envelope calculation, and here is what I concluded. (Bear in mind that I am an engineer. I know the fundamentals, but I'm far from an expert on compressible fluid flow, which is what this is about. My study was slightly more than scribbles on toilet paper; it did involve solving a differential equation in Excel, but it was nowhere near what an expert could do.)

• There may be as much as 4mph of clubhead speed lost to air resistance by a maximum-volume driver swung to an impact speed of 100mph.
• I doubt that much more than 1mph can be recovered from that by aerodynamic shaping of the clubhead, but lets say 1.5mph to be generous.
• That would provide an extra 5-6 yards at most. Not to sneeze at, but not to spend hundreds of dollars on either IMHO.

Loft

This is a biggie. Since I first wrote the Club Design Notes, more and more players are "lofting up", and driving distance is still going up. In the 1990s, John Daly could generate enough clubhead speed to get his huge drives from a 7-degree clubface. But today's big hitter, Dustin Johnson, uses a 10.5-degree loft. And most of us need more loft for our maximum distance. Here's a table I put together using TrajectoWare Drive software.

DriverClubhead Speed	Loft for Maximum Distance
115 mph	10 degrees
100 mph	12 degrees
85 mph	14 degrees
70 mph	18 degrees
< 60 mph	21 degrees

For a serious technical discussion of how loft affects driving distance, I have a detailed article on the subject.

With the arrival of super-jumbo titanium and 15-5 steel metalwoods, it was possible to find unusually large lofted clubheads that were intended to "go with" these big drivers. (Unfortunately, these are hard to find today.) For instance my wife has a very slow swing. Her "driver" is a super-jumbo 5-wood with a 200cc volume -- easily the size of the "jumbo" driver of the mid-'90s. It's a very easy hitting club, and gets the ball up in the air even though her clubhead speed is very low.

OK, digression for a true story. In the mid-'90s, we visited my wife's aunt in Florida. She lived in a senior community with an executive golf course, and played golf almost every day. She was very athletic when she was younger, and was frustrated because her senior friends were hitting good drives while she was hitting short worm-burners. I looked at her driver and asked her, "What made you buy this?" She told me a good golfer in the community had gone to advise her when she bought her clubs. He knew that the Taylor Bubble was a great driver and they had this one at a great price; he told her to get it. Well, it had a loft of 9.5°, and here is a lady in her 70s trying to get it off the tee. I told her to try my wife's tee club, which I made for her from a 21° big-head 5-wood. She immediately started hitting drives better and farther than her friends. At the end of the week, my wife's club stayed in Florida, and I had to make her another one. (I did take a 9.5° Bubble home, with her blessing. It's in my garage somewhere, I'm sure.)

So consider the golfer's swing speed -- and accuracy -- carefully in choosing a driver. Unless you're talking about a low handicapper with a lot of clubhead speed and the ability to square the clubface well every time, the best loft is probably several degrees higher than you would have guessed.

Face angle

Every metalwood head has (or should have) a specified face angle such as "1 degree open", "2 degrees closed" (or "hooked"), or "square". I don't believe that selecting a face angle is the right way to treat a golfer's slice or hook. Tom Wishon of Golfsmith disagrees. You're welcome to decide for yourself.

Adjustability

In my 2008 technology forecast for the golf industry, I projected that a significant advance in solving the combinatorics problem in clubfitting. The fitters would not need to stock a club with every possible specification; some of the specs might be adjustable, and some of the components might be interchangeable. This has come to pass, but hardly limited to a clubfitter's tool. In 2017, many of the popular commercial drivers come with significant adjustability. It isn't clear that the owners of these drivers are sufficiently knowledgeable to do effective self-fitting. Well, I'm sure some are, but many are either leaving it as it came from the store or twiddling it and hoping something will help.

There are several adjustments available on drivers in 2017: shaft adapters, adjustable weights, and hosel angle.

• Shaft adapters allow you to interchange the shaft attached to the clubhead. "You" means the clubfitter; at least that was the original intent. But a lot of commercial drivers today are sold with the adapters in the heads. If "you" -- this time the owner of the club -- want to try a reshaft, just have a shaft of the desired model made up in your flex with your favorite grip and the adapater for your driver head. At that point, you can swap shafts back and forth to your heart's content. And no torch nor shaft puller were ever involved in the entire process.
  
  
• Weights can take the form of weights sliding on a track in the sole, or screws of various weights that screw into various spots on the clubhead. You can vary the amount of weight (especially with the screws) and the placement of the weights. There is typically up to 15-20 grams of weight available for adjustment.
• If you adjust the amount of weight, you have up to perhaps 10 swingweight points to play with. That's a lot of adjustment range.
• If you adjust the placement of the weight, you are really trying to move the center of gravity. The intention is to change the dynamic loft at impact (which it can do, just a little) or the spin, due to gear effect. Tom Wishon has long maintained that it takes 30-40 grams of moveable weight to make a significant difference in spin, and built his adjustable clubs accordingly. My computer analyses agree with TaylorMade's assertion that even 15 grams moved from toe to heel can affect ball flight significantly. But -- my caveat here -- "significantly" is not enough to fix a slice; if you have a bad slice, you may not even notice the difference the weight change is making for you.
  
  
• Hosel angle purports to adjust the loft, lie, and face angle. How does it work? There is an insert in the hosel bore, which has its own bore for the shaft. But the insert's bore does not share a centerline with the hosel bore; it is something like 2° different from the hosel bore. So, depending on the way you turn the insert in the hosel, the shaft may be leaning 2° flat, upright, rearward, or forward, or some combination thereof.
• It is easy to see how this would affect the lie angle. Just turn the adapter so the shaft is 2° flat or 2° upright. In between? Well, you'll have to accept a change in the fore-and-aft tilt of the shaft, along with the desired change in lie angle.
• If the shaft is tilting fore and aft, that's loft -- right? Well, maybe. If you set up with the clubhead hovering behind the ball, rather than resting on the ground, then that is exactly loft. But...
• If you're setting up and allowing the clubhead sole to rest on the ground in its flattest position, the fore-and-aft adjustment did not affect loft at all. With the clubhead soled, the loft is simply the loft built into the clubhead, not the one you dialed on the hosel adjustment. In order to make this happen, the clubhead rotates a little to settle into its "soled" position -- so the adjustment is really about face angle, not loft at all.
Tom Wishon has made a very good video showing how the adjustable hosel really works.

Weight placement

Completely apart from the ability for the purchaser to move the center of gravity of the clubhead, consider the ability of the designer to place the CG in the first place. In particular, it is desirable to get the CG of a driver as low as possible; if you doubt this, or want to see the conditions under which it is true, see my article on exactly that subject.

Some of the modern driver head designs go to great lengths to lower the CG. This consists of two steps:

1. Free up some discretionary weight, by making the structural shell (face, sole, and crown) lighter overall. Some approaches to this:
   
   
• Use a lighter (really, greater strength-to-weight ratio) material for the shell. Clubhead manufacturers thought they were doing just that in the 1990s when they went to titanium. Then the race to get the largest volume of clubhead took over. Today, at the legal maximum of 460cc, the clubhead needs titanium just to keep its structural integrity at the 200 grams or so that a driver should be. But note that Jeff Summitt used exactly that approach with the XS Titanium 3-wood in 2013. Since a 3-wood has a much smaller volume than a driver and somewhat larger ideal weight, that freed up about 80 discretionary grams, and the result is a very effective clubhead.
• Reinforce the structure of the head in ways that more weight can be shaved from the shell than you used for reinforcement. Having seen Callaway's 2017 commercials for "Jailbreak Technology", I believe that is what the vertical bars are for behind the face. They prevent the crown and sole from buckling by attaching the crown to the sole with steel just behind the face. Thereforce, any flex is the face is just in the face, not aided by weakness in the shell behind the face.
• Use different materials for different parts of the clubhead -- strongest for the face (which absorbs a major shock), still pretty strong for the sole (which may bang on the ground -- but see step #2), and least strong for the crown (which shouldn't hit anything, unless airling baggage handlers are gorillas). That is why you see composite crowns on metalwoods, especially drivers. They can be made light and very thin, because they need to remain rigid but only under relatively small stress.
  
  
2. Use the discretionary weight by placing it as low in the clubhead as possible. Usually this is accomplished by beefing up the sole with thicker steel. It does help the strength of the club as well as making up the weight low in the club. Another approach is to make the sole, or part of the sole, out of tungsten, which is more than twice as heavy as steel. This is expensive; fabricating and bonding tungsten is harder to do than with steel or even titanium. TaylorMade did it with the original Rescue hybrid: a thick sole of tungsten and lightweight crown and face of titanium. The Orlimar fairway woods also advertised this feature, but it was just marketing. The tungsten "inserts" were just tungsten foil on the sole weighing a few grams.

Grooves

Not a performance improvement in a driver! Square grooves, V grooves, or no grooves at all: it just doesn't matter. The ball is compressed on the clubface for long enough so the friction between ball and clubface results in no slippage by the time the ball departs. All the spin, in both vertical an horizontal planes, will be imparted no matter what kind of grooves or non-grooves the driver has.

In fact, grooves may hurt performance. No, I'm not talking about spin, although much of modern driver analysis says less spin gives more distance. I'm talking about Coefficient of Restitution, AKA spring face or trampoline effect. Grooves can limit the strength of the clubface, if you make the face really thin. So it is easier to build a high-COR clubface if you leave off the grooves.