I wanted to discuss a term that I’ve neglected for the most part, mainly because I didn’t quite understand it. That term is ‘spin loft.’
Sooooo…what is spin loft?
Spin loft is the difference between the dynamic loft of the club and the attack angle.
Dynamic Loft = The loft on the club at impact.
Dynamic loft has a lot to do with shaft lean at impact.
Generally speaking, if you have more shaft lean, the loft at impact will decrease. So, let’s say you have a 7-iron that is designed with a loft of 36*. If you have enough forward shaft lean, that loft may be at 17* at impact, thus you have a dynamic loft of 17*
Attack angle is how much up or down one hits on the ball as shown in the picture below
Thus, if you have a 7-iron with a dynamic loft of 17* and an attack angle of -2*, your ‘spin loft’ would be 19*
So…why is this important?
Spin loft is about two things…compression and trajectory.
We can get a lot of compression by hitting down on the ball and getting more shaft lean. However, it may not do us that much good if we can’t get it up in the air. So, for optimal results we need a balance of compression and trajectory. In other words, we want to compress the daylights of the ball, but get it up in the air enough to allow for it to go the optimal distance.
Here’s Trackman’s ‘optimal fitting’ for drivers. Notice the attack angles and the spin lofts numbers
Take a look at the 90 mph swing with a -5* attack angle. It states that the optimal spin loft is 18.9. That means if you swing at 90 mph and your attack angle is -5* downward, in order to maximize that compression, you need a dynamic loft of 13.9*
Now if we look at a 90 mph swing with a +5 upward attack angle, the optimal spin loft is 13.4. Meaning that the optimal dynamic loft is 18.4*.
As you can see, if you hit down you need to make sure the dynamic loft of the club is not too de-lofted or the ball will go too low. Conversely, if you hit up, you need to make sure you do not have too much loft with the driver face at impact, or you will hit it too high.
So, what does that mean for irons?
I’m not sure what the optimal #’s would exactly be for certain irons, but that chart gives us a good idea. Look at the attack angles for each given swing speed. As you can see, if the attack angle is the same…we need a higher dynamic loft the faster we swing it.
With an 8-iron, the PGA Tour average is 87 mph with an attack angle around -4.5* down. Compare that to a 3-iron with a average of 98 mph and an attack angle of -3.1* down. So the dynamic loft for the 3-iron has to be less than the dynamic loft of an 8-iron for us to maximize the compression. Fortunately, it helps that the 3-iron is designed with less static loft than an 8-iron.
I’ll be looking more into spin loft in the future.