I have a set of STi irons and a set of TS2. They are identical builds. Same shafts, grips, length, and lie. I hit them both in the middle of the faces. The STi go very straight. The TS2 start left and move left. I think I’ve ruled out every possibility except that the TS2 must be closing faster than I’m used to because of lower MOI. How likely is this?
Not likely at all. The MOI’s are almost identical. The STi is 12.9413 and the TS2 is 12.4697. The difference in those two numbers are statistically insignificant. Could not tell you why you are experiencing what you are experiencing without seeing you and possibly doing some in depth analysis of the clubs. The horizontal cg location variance in those clubs is insignificant as well. Offsets are almost the same as well. Even though they are “identical” builds, there could be some variance in the shafts, but even that would be a stretch. Just know that in my 43 years experience in designing, building, fitting and playing clubs of all types, sometimes why one club performs one way and another performs differently even though they are the same or very similar, can not be determined. I wish I could give you a definitive answer, but based on the designs and the information you provided, I can’t.
Britt Lindsey
Also, remember I’m talking STi, not STi2. From what I see, the STi MOI is 14.26.
The lie could be part of it. OK on the MOI. Still, the difference is not enough to make the ball flight change the way you described. A 14.26 vs a 12.94 is still not a lot.
Britt Lindsey
Thanks Britt. Well now I think it is the lie angles. I mentioned in a question a few weeks ago that the grooves are not parallel to the center of the sole. I laid the identical clubs from each set next to each other with the heads hanging off a table, turned them a little so the toes were straight down, and really compared each two clubs at the soles. The TS2’s were all more upright. So I bent them a little flatter and will test them on the course again.