Question:
While experimenting with the MOI program available from the Golf Archives, I noticed something very interesting. I used my current 6-iron as the reference club which is a standard head, TT Flexflow shaft and standard length with a D0 swingweight. I am interested in building a new set with graphite shafts which are much lighter and graphite weighted heads such as Golfsmith OS Project or similar. Since the 7I was the base club, it’s not surprising that the computer recommends the same length for both sets’ 7I.
If you select shafts that are much lighter the swingweights seem to move one club longer and the base club get’s longer. I was wondering if two clubs have the same MOI although made from different materials, would they feel equivalent? This is of course the torsional stiffness and flex frequency were equivalent. Bud Bud Hammerton
Response:
[intro stuff deleted] If you select shafts that are much lighter the swingweights seem to move one club longer and the base club get’s longer. I was wondering if two clubs have the same MOI although made from different materials, would they feel equivalent? This is of course the torsional stiffness and flex frequency were equivalent.
This is exactly the point that caught my interest when I heard about the Swing~Sync method of club matching. Eric Cook, (of Isovibe), says that different shafts with the same frequency ARE NOT the same. His examples are Dynalite shafts are 15 cpm stiffer than Dynamics, (i.e. "The fact is that to have the same stiffness in the Dynalite as you measured in the Dynamic you would have to make the Dynalite shaft at a frequency of 240 or 15 cpm less than the Dynamic."), and TT lites are 5 cpm stiffer, (than Dynamics)… Unfortunately, the ‘conversion’ between shafts is proprietary, as is the relationship between swingspeed and MOI… Before hearing from Eric, my gut answer to your question would have been NO, they would not feel the same. Eric says that he can MAKE the different combinations "FEEL" the same, (through his shaft frequency conversion tables…), but the frequency of the two clubs will likely not be the same… db miko Mac Shack Golf London, Ontario, CANADA
Response:
While experimenting with the MOI program available from the Golf Archives, I noticed something very interesting. I used my current 6-iron as the reference club which is a standard head, TT Flexflow shaft and standard length with a D0 swingweight. I am interested in building a new set with graphite shafts which are much lighter and graphite weighted heads such as Golfsmith OS Project or similar. Since the 7I was the base club, it’s not surprising that the computer recommends the same length for both sets’ 7I.
Thanks for the plug. Some of the stuff you mention below is addressed in my Club Design notes; you might want to look at them. If you select shafts that are much lighter the swingweights seem to move one club longer and the base club get’s longer. I was wondering if two clubs have the same MOI although made from different materials, would they feel equivalent? This is of course the torsional stiffness and flex frequency were equivalent.
If you change the weights of the components, the lengths won’t be the same. But that doesn’t address what I think is your REAL question, which is, "How do we make all the clubs FEEL the same?" The usual model of club feel is to break it into to major components: 1. Heft feel. 2. Flex feel. Swingweight and MOI are both attempts to express HEFT FEEL as a single number. My articles conclude that MOI is a better number to do this. I feel it does a pretty good job as a first approximation. Some would argue that you can’t express the feel as a single number, but at least two (dead weight, plus either swingweight or MOI). BTW, in terms of freshman physics: 1. Dead weight is the zero-th moment of the mass of the club. 2. Swingweight is the first moment. 3. MOI is the second moment. Obviously, the more moments you take, the finer a characterization of the heft you have. But, IMHO, MOI is quite sufficient for a PRACTICAL characterization. As for FLEX FEEL, that’s an independent variable, made up of vibration frequency, torque, kick point, and possibly other things. I believe this addresses what you’re asking. Cheers! Dave
Response:
Some of the stuff you mention below is addressed in my Club Design notes; you might want to look at them.
Read them all with great interest, along with all the other information I could find at the Golf Archives. If you change the weights of the components, the lengths won’t be the same.
Agreed. But that doesn’t explain why the swing weight of the REFERENCE club tend to go up. My steel shafted REFERENCE club is a D0 swingweight and your scale turns it into a D0.9 – D1.1 depending on components. The usual model of club feel is to break it into to major components: 1. Heft feel. 2. Flex feel. Swingweight and MOI are both attempts to express HEFT FEEL as a single number. My articles conclude that MOI is a better number to do this.
So then my question has really two parts. Irregardless of material, swingweight, or static weight will two clubs with the same MOI have the same HEFT FEEL? As for FLEX FEEL, that’s an independent variable, made up of vibration frequency, torque, kick point, and possibly other things.
It appears to me that changing materials of club construction is problematic at best. From the responses I have recieved and articles I’ve read it seems that even if a steel and graphite shaft have the same frequency, torsional stiffness (torque), flex, and weight there is now way to say with any degree of certainty that they will feel the same or even be similar in feel? Is that correct? I am new components and club building, I don’t want to be one of those people you wrote about in your clubbuilding articles who built "turkeys." I would like to build a set of nice clubs that I will grow to love and play well with for the next 5 to 10 years. Would a better way of determining which clubs to model would be to try out many manufacturers graphite shafted clubs, instead of modeling after a club I am already infinately familiar with? Sorry about all the questions, but I want to be well informed and prepared for any result I may get. Bud Hammerton
Response:
If you change the weights of the components, the lengths won’t be the same. Agreed. But that doesn’t explain why the swing weight of the REFERENCE club tend to go up. My steel shafted REFERENCE club is a D0 swingweight and your scale turns it into a D0.9 – D1.1 depending on components.
You raise an interesting point. I was confused by this too, until I thought about it for a while. Here’s what’s going on (if I understand what you’re asking): OK, you’ve changed something about the REFERENCE club to go from your favorite 7-iron to the new 7-iron. (If you kept the components the same and just tried to MOI-match the set you have, you wouldn’t have observed the change in swingweight for the reference club.) Now there’s something different in the mix, and it may be impossible to match BOTH the MOI and the swingweight of the old reference club to the new one. Work through the math yourself with the simplest form of the equations, and convince yourself. Just change, say, the shaft weight in the equation, and find the length to get a swingweight match and the length to get an MOI match. Then compute the MOI and swingweight for both new clubs. The equations to use, to keep it real simple, make some gross assumptions; for instance, they ignore grip weight, so the absolute value of swingweight will be way off; the degree of match, however, will not be affected. MOI = L^2*(H + S/3) Swingweight = L*(H + S/2) – 14*(H + S) The usual model of club feel is to break it into to major components: 1. Heft feel. 2. Flex feel. Swingweight and MOI are both attempts to express HEFT FEEL as a single number. My articles conclude that MOI is a better number to do this. So then my question has really two parts. Irregardless of material, swingweight, or static weight will two clubs with the same MOI have the same HEFT FEEL?
I believe that MOI is the best single number to represent the HEFT FEEL. I believe that you can indeed feel things other than MOI in the heft, but MOI is the only one that matters during the downswing when it counts. The analysis that leads me to this conclusion is available at dunkin.princeton.edu in my "Swingweight Notes". It’s worth noting that Taylor Made’s design staff feels there’s more to it, and the Bubble Shaft is based on that. (I.e.- MOI is very important, but INDEPENDENTLY the CG of the finished club also affects distance.) As for FLEX FEEL, that’s an independent variable, made up of vibration frequency, torque, kick point, and possibly other things. It appears to me that changing materials of club construction is problematic at best. From the responses I have recieved and articles I’ve read it seems that even if a steel and graphite shaft have the same frequency, torsional stiffness (torque), flex, and weight there is now way to say with any degree of certainty that they will feel the same or even be similar in feel? Is that correct?
Again, designers would love to be able to find a single number to represent FLEX FEEL. The most complete attempt I’ve seen is the Dynacraft DSFI, as described by Summitt & Wishon in "The Modern Guide to Shaft Fitting". If you’re really interested in this stuff, and would like to see 200 pages of well-researched and interesting test results and analysis — on EVERYTHING about shafts — I can highly recommend this book. … Would a better way of determining which clubs to model would be to try out many manufacturers graphite shafted clubs, instead of modeling after a club I am already infinately familiar with? Sorry about all the questions, but I want to be well informed and prepared for any result I may get.
You’re asking great questions, that show a lot more insight than most beginners. I look forward to your making positive contributions once you get into this. In the meantime, to address your specific question… My own approach is to go at things kind of incrementally. If I build a "now-for-something-completely-different" club, I’ll never be sure what made it so good or so bad. I try not to change more than two things from a club I’m familiar with, when I try something new. A more careful researcher (with no eye on the pocketbook) would only change one thing at a time; but I don’t do this for money, so I have to shortcut A LITTLE. Cheers! Dave