# Driver Head Weight and Club Length

Dave Tutelman -- October 28, 2012

## Variable Club Length

In the constant-length studies above, the club's feel -- its "heft" -- varied considerably as we changed the head weight. One of the problems this produced is that the gains are limited by the torque-velocity curve. But suppose we could use a lighter head, but still preserve the "heft" of the club, the load it presents to the golfer. (Heft is normally measured by swingweight or moment of inertia of the club.) If we can do this, we might be able to keep the angular velocity profile the same from club to club, and not incur additional losses to torque-velocity.

There are other ways to use a lighter head to get more clubhead speed, while not losing heft. An obvious one is, lengthen the club itself as the head gets lighter. This not only utilizes the light head, but provides a longer radius. If we can keep the angular velocity up, the longer radius itself should give higher clubhead speed. And indeed it works that way.

### Bernie Baymiller's assertions

Bernie Baymiller, a clubfitter in a retirement community, has often held forth on how older golfers can regain lost distance by using a longer driver. His assertion is that a longer driver, together with a lighter head and shaft so the swingweight doesn't overwhelm the golfer, gives a substantial increase in distance. His estimate is 25-30 yards for himself, at age 75 when he wrote about it.

Posted to ShopTalk, March 22, 2009:
Why mess around with the short clubs when you can go to 48" club length? A 193 gram BOM plugged to 1½" bore depth with a 58 gram Pure Energy A (about 55 trimmed) and 43 gram Winn Excel midsize comes in at about 296 grams and D9. If I can swing that at 75, so can you. It's worth 25 to 30 yards beyond what I get with a 45" driver and I seldom miss a fairway with it. (Of course, I'm seldom over 260 yards with it anymore.)
Bernie is writing to clubmakers here. For those of you who are not:
• BOM is a component driver clubhead, the Bang-O-Matic from Bang Golf.
• Pure Energy A is the Pure Energy shaft from SK Fiber shafts, in an "A" flex.
• Winn Excel midsize is a grip.
• D9 is a swingweight. (It is a much heavier swingweight than the driver I built.)
This is a huge gain! It works out to 8-10 yards per inch. Bernie has cited a number like that recently, but I am unable to find the post at the moment. If I run across it, I will add the quote to this article.

The rest of the article will be spent in trying to quantify the gain, to test Baymiller's assertion.

### Another computer study

Let's repeat the computer study, using a longer shaft as well as lighter head weight. We will use the same 45" club with a 200g head and swing it with the same SwingPerfect model, but adjust the length as the head weight changes. We will change length and weight so that we keep the same whole-club moment of inertia (MOI) the same.[3]

The table below has the results of the computer study. A few points about the table:
• Obviously, we added a 'length' column. The length is computed to keep the club MOI constant as the head weight changes. We use the same 65g shaft weight for all the rows of the table.
• The clubhead loft is computed as follows:
• Start with the dynamic loft that TrajectoWare Drive says you need for maximum carry distance, at the clubhead speed computed in SwingPerfect.
• Subtract 2º, assuming we get an additional 2º of loft from shaft bend. (We made this same assumption in the constant-length study.)
• If this one does not make sense to you, look below where we discuss wrist angle. Add 82% of the wrist angle, which contributes to the loft. (Positive wrist angle subtracts loft from the club.) Wrist angle occurs in the swing plane, which is about 55º for a driver. Because the plane is not vertical, the wrist angle contributes to both loft and clubface closure, in the proportion of the sine to the cosine of the swing plane. Sin(55º) is about 82%, so we want to add 0.82 of the wrist angle to the club loft. Cosine(55º) is about 57%, which represents the angle the face is open at impact.
• The upper rows are shaded in red because they represent non-conforming clubs. The USGA and R&A rules limit the club length to 48". This corresponds to a clubhead weight of 173 grams. I included the extra rows to get a better picture of the trend, but you can't build those drivers. Even if they were not illegal clubs, it would be hard to find shafts long enough to build them over 50 inches.

 Head weight Length Clubhead speed Ball speed Carry distance Wrist angle Clubhead loft 100 60.74 134.0 166 270 20 23.4 110 58.39 128.8 164 267 17.8 22.3 120 56.29 124.1 162 263 15.9 20.4 130 54.40 120.1 160 260 13.1 18.8 140 52.69 116.4 158 256 10.8 17.2 150 51.14 112.9 155 252 9.0 16.2 160 49.71 109.8 153 248 6.7 14.5 170 48.39 106.9 151 243 5.4 13.9 180 47.18 104.4 149 240 3.2 13.3 190 46.05 102.0 147 236 1.0 10.5 200 45.00 99.6 145 232 -0.1 10.2 210 44.02 97.6 143 229 -2.0 8.9 Given Computed to give constant MOI From SwingPerfect From TrajectoWare Drive From TrajectoWare Drive From SwingPerfect Optimum loft - shaft bend + .8*wrist angle

The result is a somewhat greater increase of distance than if the club length were held constant, but not as great as Baymiller claims.
• Baymiller claims 25-30 yards in going from a 45" driver to a 48" driver.
• The table above shows a gain of about 10 yards going from 45" to 48". (This is less than the simplistic/optimistic calculation we did earlier: 10yd vs 16yd.)
• As a side comment we will get back to later, a constant-length driver shows a gain of 5 yards with just the change of head weight required to go from 45" to 48". (That is, a 45" driver where all we do is change the head weight from 200g to 173g. We know this from the first computer study above.)

### A few more computer studies

One question that immediately comes to mind is how distance varies with head weight at the longest allowable driver length, 48 inches. If a longer driver gives more distance, then what is the most distance we could possibly get from a longer driver?

We already did this at 45", the conventional driver length. Let's run through it again, at 48 inches, just for fun. For this study, we're not going to bother keeping track of wrist angle or loft; we just want to see how much of the distance gain is due to the longer club and how much to the lighter clubhead.

 Head weight Length Clubhead speed Ball speed Carry distance 100 48" 124.5 154 247 110 48" 121.4 154 248 120 48" 118.8 155 249 130 48" 116.1 154 249 140 48" 113.6 154 248 150 48" 111.2 153 247 160 48" 108.9 152 245 170 48" 106.8 151 243 180 48" 104.9 150 242 190 48" 102.8 148 239 200 48" 100.9 147 236 210 48" 99.1 146 233 Given Maximum legal length From SwingPerfect From TrajectoWare Drive From TrajectoWare Drive

The maximum-length driver shows a maximum distance at a head weight of 125g. That is remarkably similar to the 45" constant-length driver, with a maximum at 130g. The maximum distance here is a longer distance: 248yd rather than 243yd at 45". The extra 3 inches is worth 5 yards. Not a lot but worth going after, all other things being equal. (However, try to find a driver head weighing 125 or 130 grams. They are not made.)

Just for completeness, let's see what happens when you change club length and leave the head weight the same. Again, we are ignoring wrist angle and loft, to be solved the same way we did above. And again, we have marked in red the non-conforming driver lengths.

 Head weight Length Clubhead speed Ball speed Carry distance 200 60.74 104.7 153 247 200 58.39 104.1 152 246 200 56.29 103.5 151 244 200 54.40 103.2 150 243 200 52.69 102.6 149 241 200 51.14 102.2 149 240 200 49.71 101.6 148 238 200 48.39 101.2 147 237 200 47.18 100.6 146 235 200 46.05 100.2 146 234 200 45.00 99.6 145 232 200 44.02 99.2 144 231 Given Lengths are the constant- MOI lengths From SwingPerfect From TrajectoWare Drive From TrajectoWare Drive